Optical Coordinate Measurement Research Articles

Fretting and Tribocorrosion of Modular Dual Mobility Liners: Role of Design, Microstructure, and Malseating

BackgroundModular dual mobility (DM) bearings have a junction between a cobalt chrome alloy (CoCrMo) liner and titanium shell, and the risk of tribocorrosion at this interface remains a concern. The purpose of this study was to determine whether liner malseating and liner designs are associated with taper tribocorrosion. MethodsWe evaluated 28 retrieved modular DM implants with a mean in situ duration of 14.6 months (range, 1 to 83). There were 2 manufacturers included (12 and 16 liners, respectively). Liners were considered malseated if a distinct divergence between the liner and shell was present on postoperative radiographs. Tribocorrosion was analyzed qualitatively with the modified Goldberg Score and quantitatively with an optical coordinate-measuring machine. An acetabular shell per manufacturer was sectioned for metallographic analysis. ResultsThere were 6 implants (22%) that had severe grade 4 corrosion, 6 (22%) had moderate grade 3, 11 (41%) had mild grade 2, and 5 (18.5%) had grade 1 or no visible corrosion. The average volumetric material loss at the taper was 0.086 ± 0.19 mm3. There were 7 liners (25%) that had radiographic evidence of malseating, and all were of a single design (P = .01). The 2 liner designs were fundamentally different from one another with respect to the cobalt chrome alloy type, taper surface finish, and shape deviations. Malseating was an independent risk factor for increased volumetric material loss (P = .017). ConclusionsDM tribocorrosion with quantifiable material loss occurred more commonly in malseated liners. Specific design characteristics may make liners more prone to malseating, and the interplay between seating mechanics, liner characteristics, and patient factors likely contributes to the shell/liner tribocorrosion environment. Level of EvidenceLevel III.

Influence of the Manufacturing Trinomial (Technology, Printer, and Material) on the Marginal and Internal Discrepancies of Printed Metal Frameworks for the Fabrication of Tooth-Supported Prostheses: A Systematic Review and Meta-analysis.

The purpose of this systematic review and meta-analysis was to compare the influence of fabrication method (conventional, subtractive, and additive procedures) and manufacturing trinomial (technology, printer, and material combination) on the marginal and internal fit of cobaltchromium (Co-Cr) tooth-supported frameworks. An electronic systematic review was performed in five data bases: MEDLINE/PubMed, Embase, World of Science, Cochrane, and Scopus. Studies that reported the marginal and internal discrepancies of tooth-supported Co-Cr additive manufacturing (AM) frameworks were included. Two authors independently completed the quality assessment of the studies by applying the Joanna Briggs Institute Critical Appraisal Checklist for Quasi-Experimental Studies. A third examiner was consulted to resolve lack of consensus. A total of 31 articles were included and classified based on the evaluation method: manufacturing accuracy, the dual- or triple-scan method, stereomicroscope, optical coordinate measurement machine, microCT, profilometer, and silicone replica. Six subgroups were created: 3D Systems, Bego, Concept Laser, EOS, Kulzer, and Sisma. Due to the heterogeneity and limited data available, only the silicone replica group was considered for meta-analysis. The metaanalysis showed a mean marginal discrepancy of 91.09 μm (I2 = 95%, P < .001) in the conventional group, 77.48 μm (I2 = 99%, P < .001) in the milling group, and 82.92 μm (I2 = 98%, P < .001) in the printing group. Additionally, a mean internal discrepancy of 111.29 μm (I2 = 94%, P < .001) was obtained in the conventional casting group, 121.96 μm (I2 = 100%, P < .001) in the milling group, and 121.25 μm (I2 = 99%, P < .001) in the printing group. Manufacturing method and selective laser melting (SLM) metal manufacturing trinomial did not impact the marginal and internal discrepancies of Co-Cr frameworks for the fabrication of tooth-supported restorations.

Comparison of optical 3D scanner and coordinate measurement system from the standpoint of macro-geometry measurement

The aim of the experiment described in the paper was to determine the possibility of using an optical 3D scanner to measure the macro-geometry of cutting tools. To verify this possibility, a precise component was measured, and the accuracy of optical 3D scanner was compared to a tactile coordinate measurement machine. A precise cemented carbide rod was used as a reference part and the measurement data were compared with the measurement result from the ZEISS Prismo coordinate measurement machine. The data obtained from the measurements were evaluated and compared. The experiment was carried out so that the use of an optical 3D scanner to measure cutting tools could be verified based on the desired requirements. Both dimensions and geometrical tolerancing – circularity were measured. The experiment has shown that an optical 3D scanner can achieve sufficient accuracy for the purpose of measuring macro-geometry of cutting tools.

The metrological structural resolution for dimensional x-ray CT: analysis of the comparability between the CEB and the PBS method

The metrological structural resolution (MSR) describes the size of the smallest surface feature that can be measured dimensionally with a given accuracy. Several methods to determine the MSR for dimensional x-ray CT (dXCT) have been proposed in the past, two of which are compared and related in this publication, i.e. the curved-edge based (CEB) and the profile-based spectral (PBS) method. Both methods consider the surface structure as being described by a single surface on the relevant local scale and are also suitable for the application to optical or tactile coordinate measurement systems (CMSs). The CEB method evaluates the radii of circular shapes to determine the width of the Gaussian filter that describes the filtering of the surface by the CMS. The PBS method evaluates the instrument transfer function (ITF) determined by means of the measurement of a surface profile with a broad-band spatial frequency spectrum with a finite cut-off frequency. The PBS method yields the threshold wavelength for which the amplitude of the ITF drops below a certain level. While the resulting quantities of the two methods are very different they evaluate the same characteristic of the CMS. In this publication an analytical relation between those results is derived and shown to exist which is used to define the MSR. Simulated CT scans as well as dXCT measurements are performed to verify this relation. The results for the MSR obtained from both methods are consistent and deviations to the expectations based on theory are within a reasonable range.

METROLOGICAL CHARACTERIZATION OF OPTICAL 3D COORDINATE MEASUREMENT SYSTEMS – COMPARISON OF ALTERNATIVE HARDWARE DESIGNS AS PER ISO 10360

Abstract. This research focuses on the characterization of the metrology of Optical 3D Coordinate Measurement Systems (O3DCMS). The focus is set on the identification and execution of the procedure indicated by the currently active technical standards related to industrial O3DCMS, for their metrological assessment, objective comparison, and performance tracking. This work leads to the implementation of an ad hoc software for the execution of the standard tests by the ISO 10360-13 standard. The implemented software application is employed in a real-case scenario for evaluating the performances of an industrial 3D scanner based on structured light. The specific hardware components to be assessed are two light sources of the active stereoscopic vision system, named Digital Light Projectors (DLP). The case study applies the procedures and metrics indicated by the active standards to objectively compare two alternative hardware design of the system under test. This results in the identification of the most performing hardware configuration, allowing the selection of the best system design, basing on objective metrological parameters.

Evaluating parametric uncertainty using non-linear regression in fringe projection

Optical coordinate measurement systems, such as fringe projection systems, offer fast, high-density measurements of arbitrary surface topographies. The versatility, speed and information density of fringe projection measurements make them attractive as in-situ measurement devices and autonomous inspection systems. However, the complex nature of the measurement process makes evaluating uncertainty from a fringe projection measurement complex – even in the hypothetical simple case where the accuracy of a measurement is limited only by the accuracy in the quantities that define a measurement from an indication; named system parameters here. In this paper, by validating a series of assumptions, a method to explore the uncertainty in the system parameters of a fringe projection system is given. The results of this investigation imply the common distortion model (the Brown-Conrady model) is not specific enough to the camera or projector of a fringe projection system to evaluate its uncertainty.

Do total shoulder arthroplasty implants corrode?

Total shoulder arthroplasty (TSA) has become the gold-standard treatment to relieve joint pain and disability in patients with glenohumeral osteoarthritis who do not respond to conservative treatment. An adverse reaction to metal debris released due to fretting corrosion has been a major concern in total hip arthroplasty. To date, it is unclear how frequently implant corrosion occurs in TSA and whether it is a cause of implant failure. This study aimed to characterize and quantify corrosion and fretting damage in a single anatomic TSA design and to compare the outcomes to the established outcomes of total hip arthroplasty. We analyzed 21 surgically retrieved anatomic TSAs of the same design (Tornier Aequalis Pressfit). The retrieved components were microscopically examined for taper corrosion, and taper damage was scored. Head and stem taper damage was quantitatively measured with a non-contact optical coordinate-measuring machine. In selected cases, damage was further characterized at high magnifications using scanning electron microscopy. Energy-dispersive x-ray spectroscopy and metallographic evaluations were performed to determine underlying alloy microstructure and composition. Comparisons between groups with different damage features were performed with independent-samples t tests; Mann-Whitney tests and multivariate linear regression were conducted to correlate damage with patient factors. The level of statistical significance was set at P<.05. The average material loss for head and stem tapers was 0.007 mm3 and 0.001 mm3, respectively. Material loss was not correlated with sex, age, previous implant, or time in situ (P>.05). We observed greater volume loss in head tapers compared with stem tapers (P=.002). Implants with evidence of column damage had larger volumetric material loss than those without such evidence (P=.003). Column damage aligned with segregation bands within the alloy (preferential corrosion sites). The average angular mismatch was 0.03° (standard deviation, 0.0668°), with negative values indicating distal engagement and positive values indicating proximal engagement. Implants with proximal engagement were significantly more likely to have column damage than those with distal engagement (P=.030). This study has shown not only that the metal components of TSA implants can corrode but also that the risk of corrosion can be reduced by (1) eliminating preferential corrosion sites and (2) ensuring distal engagement to prevent fluid infiltration into the modular junction.

Optimisation of camera positions for optical coordinate measurement based on visible point analysis

In optical coordinate measurement using cameras, the number of images, and positions and orientations of the cameras, are critical to object accessibility and the accuracy of a measurement. In this paper, we propose a technique to optimise the number of cameras and the positions of these cameras for the measurement of a given object using visible point analysis of the object's computer aided design data. The visible point analysis technique is based on a hidden point removal approach; this technique is used to detect which surface points on the object are visible from a given camera position. A genetic algorithm is used to find the set of positions that provide optimum surface point density and overlap between views, while minimising the total number of camera images required. The genetic algorithm is used to minimise the measurement data processing time while maintaining optimum surface point density. We test this optimisation procedure on four artefacts and the measurements are shown to be comparable to that from a traceable contact co-ordinate measurement machine. We show that using our procedure improves the measurement quality compared to the more conventional approach of using equally spaced images. This work is part of a larger effort to fully automate and optimise optical coordinate measurement techniques.

REFINEMENTS AND INTRODUCTION OF PHOTOGRAMMETRIC ELEMENTS TO AN EXPERIMENTAL TRILATERATION BASED OPTICAL METROLOGY SYSTEM

Abstract. OPTIMUM is a novel optical coordinate measurement system designed to determine the location of omnidirectional targets within a large volume, the previous version of the system could determine the targets location with an uncertainty of 50 × 10−6 m. This paper describes some of the limitations of the original embodiment and changes being developed to address them. Version 2 of the system aims to solve the limitations of version 1 by integrating photogrammetric processes into the design and control processes of the system, along with redesigning the mechanical and optical relationships. The redesigned instrument will result in the ability to fully automate the initial calibration process and to allow for real-time processing of the measurement algorithms.

Volumetric error modelling of a stereo vision system for error correction in photogrammetric three-dimensional coordinate metrology

Optical three-dimensional coordinate measurement using stereo vision has systematic errors that affect measurement quality. This paper presents a scheme for measuring, modelling and correcting these errors. The position and orientation of a linear stage are measured with a laser interferometer while a stereo vision system tracks target points on the moving stage. With reference to the higher accuracy laser interferometer measurement, the displacement errors of the tracked points are evaluated. Regression using a neural network is used to generate a volumetric error model from the evaluated displacement errors. The regression model is shown to outperform other interpolation methods. The volumetric error model is validated by correcting the three-dimensional coordinates of the point cloud from a photogrammetry instrument that uses the stereo vision system. The corrected points from the measurement of a calibrated spherical artefact are shown to have size and form errors of less than 50 μm and 110 μm respectively. A reduction of up to 30% in the magnitude of the probing size error is observed after error correction is applied.

Influence of ceramic firing on marginal gap accuracy and metal-ceramic bond strength of 3D-printed Co-Cr frameworks

Statement of problemThe marginal gap and ceramic bond strength of metal-ceramic restorations are important for success. However, studies evaluating the marginal gap and ceramic bond strength of fixed partial dentures (FPDs) produced with 3D printing technologies such as selective laser melting (SLM) are scarce. PurposeThe purpose of this in vitro study was to investigate the marginal gap of cobalt-chromium (Co-Cr) alloy frameworks produced by SLM technology before and after ceramic firing. Additionally, the metal-ceramic bond strength was evaluated with the Schwickerath crack-initiation test according to the International Standards Organization (ISO) 9693-1:2012. Material and methodsConventional impressions were made, and the definitive cast of a patient requiring a 4-unit FPD was scanned. After designing the FPD, the files were sent to a service center for the fabrication of a metal master model, 80 Co-Cr frameworks, and 80 flat specimens (25×3×0.5 mm) with SLM technology. The marginal gap between frameworks and the abutment tooth of the metal master model was nondestructively measured by using an optical coordinate-measuring machine. A total of 80 sets, consisting of 1 framework and 1 flat specimen, were sent to 80 dental laboratory technicians for ceramic firing. Detailed instructions for correct manipulation of the framework and flat specimen were provided. The marginal gap was remeasured, and the 3-point bend test was used to evaluate metal-ceramic bond strength. ResultsOnly 28 of the 80 dental technicians returned the specimens within a prespecified time and/or in adequate condition. The mean ±standard deviation marginal gap of the framework before ceramic firing was 25 ±9 μm and 34 ±12 μm after firing. The difference was statistically significant (P=.001). The mean ±standard deviation 3-point bend strength was 33 ±9 MPa. ConclusionsCeramic firing affected the marginal gap; however, all Co-Cr frameworks had a marginal gap lower than 120 μm, which is reported to be a clinically acceptable limit. Most of the specimens (80%) had a metal-ceramic bond strength value higher than the 25-MPa ISO 9693 requirement. Five of 28 dental laboratory technicians were not able to comply with ceramic firing instructions.

Rational arrangement of direct plummets in concrete dams

Introduction. The design and construction of high hydroelectric installations are closely related to in-situ observations and studies over their condition and operation, which are the most reliable and effective means of verifying the reliability of calculation methods and design solutions. According to the results of the in-situ observations and studies during the construction and operation of dams, to monitor their condition by means of measurement systems, laboratory tests and calculation methods, unified methods can be developed for equipping the installations with devices on a unified principle. Currently, there is quite a lot of experience in the development and application of methods of in-situ research. New-type devices for measuring displacements, stresses in concrete, filtration flows and piezometric levels are developed. Automated systems for monitoring the behavior of hydraulic structures during the construction, filling of the reservoir and operation are installed. Modern satellite systems GLONASS and GPS are used. Materials and methods. The research was carried out on the arch dam of Inguri HEPS by means of 2177 measuring systems, 46 of which are direct and opposite plummets. The body of the dam has three direct plummets and one in each of the rocky bank abutments. Displacements relative to the plummets were measured with an optical coordinate-measuring apparatus. Statistical analysis methods were used to process the measurement data. Results. A technique of rational direct plummet arrangement in concrete dams was fine-tuned using statistical analysis methods and Barlow-Hunter-Proshan mathematical model based on the modern experience of in-situ observations and research. The type of distribution law of dam horizontal displacements was determined by means of analyzing the histograms of the measured indicators of the static state of the installation. The required number of plummets for the key console of the Inguri arch dam was specified. This technique was used in practice for designing high concrete dams. Conclusions. Munlti-year experience in the research and operation of the Inguri HEPS arch dam allowed assessing the compliance of the mounted measuring systems with special control requirements and allocating the necessary amount of them for monitoring the strength and stability of the installation. The proposed methods of in-situ research data analysis based on the theory of probability, statistics and reliability were used in the design of the Hudoni HEPS dam.

Laboratorium Wzorcujące ITA

In the paper a process of implementation of management system according to PN-EN ISO/IEC 17025 for ITA Calibration Laboratory was presented. Laboratory was granted an accreditation from PCA regarding calibration of universal testing machines and technological devices for tensile forces and compression forces as well as coordinate measurement systems with optical distance sensors and coordinate measurement systems based on technique of optical scanners for rotary symetrical work pieces.

Relative posture-based kinematic calibration of a 6-RSS parallel robot by optical coordinate measurement machine

In this article, a relative posture-based algorithm is proposed to solve the kinematic calibration problem of a 6-RSS parallel robot using the optical coordinate measurement machine system. In the ...

Fusion of photogrammetry and coherence scanning interferometry data for all-optical coordinate measurement

Multisensor data fusion is an approach to enlarge the potential applicability of measuring techniques and improve accuracy, taking advantage of the strengths of different techniques. In this work, we present a new method for the fusion of photogrammetry and coherence scanning interferometry (CSI) data. This method allows the photogrammetry data to be accurately scaled with reference to the CSI data, and in turn the exact locations of multiple CSI measurements can be determined in the coordinate system defined by photogrammetry. The culmination of this work is to allow for high-accuracy three-dimensional optical coordinate measurement and surface topography measurement simultaneously.

Performance evaluation of a portable 3D vision coordinate measuring system

ABSTRACTIn this work, we present a portable 3D vision coordinate measuring machine (PCMM) for short range-real time photogrammetry. The PCMM performs 3D measurements of points using a single camera in combination with a hand tool and a computer. The hand tool has infrared LEDs serving as photogrammetric targets. The positions of these targets were pre-calibrated with an optical coordinate-measuring machine defining a local coordinate system on the hand tool. The camera has an infrared filter to exclude all ambient light but infrared targets. Positions of the imaged infrared targets are converted to 3D coordinates using pixel positions and pre-calibrated positions of the targets. Also, we present a set of criteria for selecting the infrared LEDs and the camera filter, a camera calibration method, a tracking and POSE algorithms, and a 3D coordinate error correction for the PCMM. The correction is performed using the PCMM as a range meter, which implies comparing the 3D coordinate points of the PCMM with a coordinate measuring machine, and then generating a look up table (LUT) for correction. The global error of the PCMM was evaluated under ASME B89.4.22-2004. Sphere and single point errors were around 1 mm, volumetric error were under 3 mm.

A Model to Determinate the Influence of Probability Density Functions (PDFs) of Input Quantities in Measurements

A method for analysing the effect of different hypotheses about the type of the input quantities distributions of a measurement model is presented here so that the developed algorithms can be simplified. As an example, a model of indirect measurements with optical coordinate measurement machine was employed to evaluate these different hypotheses. As a result of the different experiments, the assumption that the different variables of the model can be modelled as normal distributions is proved.

Towards in-process x-ray CT for dimensional metrology

X-ray computed tomography (CT) offers significant potential as a metrological tool, given the wealth of internal and external data that can be captured, much of which is inaccessible to conventional optical and tactile coordinate measurement machines (CMM). Typical lab-based CT can take upwards of 30 min to produce a 3D model of an object, making it unsuitable for volume production inspection applications. Recently a new generation of real time tomography (RTT) x-ray CT has been developed for airport baggage inspections, utilising novel electronically switched x-ray sources instead of a rotating gantry. This enables bags to be scanned in a few seconds and 3D volume images produced in almost real time for qualitative assessment to identify potential threats. Such systems are able to scan objects as large as 600 mm in diameter at 500 mm s−1. The current voxel size of such a system is approximately 1 mm—much larger than lab-based CT, but with significantly faster scan times is an attractive prospect to explore. This paper will examine the potential of such systems for real time metrological inspection of additively manufactured parts. The measurement accuracy of the Rapiscan RTT110, an RTT airport baggage scanner, is evaluated by comparison to measurements from a metrologically confirmed CMM and those achieved by conventional lab-CT. It was found to produce an average absolute error of 0.18 mm that may already have some applications in the manufacturing line. While this is expectedly a greater error than lab-based CT, a number of adjustments are suggested that could improve resolution, making the technology viable for a broader range of in-line quality inspection applications, including cast and additively manufactured parts.

Measurement of Industrial Robot Trajectories With Reorientations

The increasing use of industrial robots in different applications raises the demand of the robots performance. This yields to the request for reliable data for the performance characteristics of industrial robots. In this paper a measurement solution for dynamic industrial robot motion measurement with a significant amount of reorientations is presented. The proposed method uses an optical coordinate measurement system with light emitting diodes (LEDs) as active markers. The reorientations of the robots tool increases the difficulty of temporary occlusion of markers, disappearance of markers and reappearance of previously hidden markers. An automated marker registration system based on quality evaluation for single LED measurements has been developed to allow flexible maker setups and decrease the possibility of measurement errors. To interpret the measurement data, an additional error metric for the according ISO standard for measuring robot motion is proposed.

Swing arm optical coordinate-measuring machine: high precision measuring ground aspheric surfaces using a laser triangulation probe

The swing arm optical coordinate-measuring machine (SOC), a profilometer with a distance measuring interferometric sensor for in situ measurement of the topography of aspheric surfaces, has shown a precision rivaling the full aperture interferometric test. To further increase optical manufacturing efficiency, we enhance the SOC with an optical laser triangulation sensor for measuring test surfaces in their ground state before polishing. The calibrated sensor has good linearity and is insensitive to the angular variations of the surfaces under testing. Sensor working parameters such as sensor tip location, projection beam angle, and measurement direction are calibrated and incorporated in the SOC data reduction software to relate the sensor readout with the test surface sag. Experimental results show that the SOC with the triangulation sensor can measure aspheric ground surfaces with an accuracy of 100 nm rms or better.