Coordinate Measuring Machine Research Articles

Influence of the scanning path on the accuracy of intraoral scanners in the implanted edentulous patient: an in vitro study.

The aim of this in vitro study was to investigate the influence of scan paths on the accuracy (trueness and precision) of intra-oral scanning of an implant impression on an edentulous patient. An epoxy resin maxillary model was made with 6 bone level implants (NobelParallel Conical Connection RP, NobelBiocare®). The implants were placed at the spot of the first incisor, the canine and the first molar. The trans gingival component (Multi-unit, NobelBiocare®) was screwed onto the implants. The scanbodies (IO 2C-A, Elos Accurate®) were then screwed onto the multi-units. The model was run through a coordinate measurement machine to obtain a control cast. Then, five different scanning paths, respectively the zigzag technique (ZZT), the zigzag technique with palatal (ZZTP), the wrap technique (WT), the wrap technique with palatal (WTP), and the big zigzag technique (BZZT), were applied by a single operator. Finally, each scan was compared to the control model. Results were assessed by one-way ANOVA and linear mixed effects models at P<0.05. The study showed that scan paths ZZT and ZZTP had significantly lower absolute positioning errors and residual mean square errors than the others (P<0.0001). For distances between consecutive implant axes and for absolute vertical errors, their superiority was borderline (P<0.10). Overall, techniques ZZT and ZZTP were equally performant and proved to be the most accurate. This in vitro experimental study demonstrates that the scan path can have an influence on the accuracy of the optical impression for full arch rehabilitation on implants.

Investigation on the effect of corner error in WEDM taper cutting process of Ti–6Al–4V

ABSTRACT Wire Electrical Discharge Machining (WEDM) is a non-conventional manufacturing method known for producing high-quality surface finishes and relies on the condition that materials conduct electricity. However, corner inaccuracies arise in workpieces during corner cuts with this method. This study aims to investigate corner inaccuracies using a novel approach involving oblique cutting and considering parameters such as wire tension (WT), corner angle, taper ratio, nozzle gap, and dielectric flow rate (LQ). The lower and upper corners resulting from taper cutting are analyzed separately. Initially, the parameters were determined, and the experimental design was established using the Taguchi method. Subsequently, the Coordinate Measuring Machine (CMM) was employed to determine the point positions of the specimens. A unique software-based method was then utilized to analyze the obtained point positions, revealing deficiencies in the expected corner areas and exposing errors. Ultimately, the analysis of the results was conducted employing the ANOVA method, offering insights into the verification and outcomes of the conducted experiments. The study concludes that, when examining corner inaccuracies, the most influential parameters are wire tension and dielectric flow rate for both lower and upper corners in taper cutting.

Trueness of Crown Preparation Dies in Dental Models: An In Vitro Assessment of Digital and Analog Workflows.

To assess crown die trueness using additive manufacturing (AM) based on intraoral scanning (IOS) data and compare it with stone models. Crown dies with four finish line types- equigingival shoulder (SAE), subgingival shoulder (SAS), equigingival chamfer (CAE), and subgingival chamfer (CAS)-were incorporated into a reference model and scanned with a coordinate measurement machine (CMM; n = 1 scan). Trios4 (3Shape) scans generated a second reference dataset (IOS; n = 10 scans). Using scans, crown dies were produced with two different 3D printers (MAX UV385 [Asiga] and NextDent 5100 [3DSystems]; n = 10 per system). Stone dies were created from conventional impressions (n = 10). Specimens were digitized with a laboratory scanner (E4, 3Shape). Trueness was evaluated with Geomagic Control X (3DSystems). Data analysis was done using Shapiro-Wilk, Levene, ANOVA, and t tests (α < .05). All crown dies fell within the clinically acceptable trueness range (150 μm). IOS exhibited significantly lower (P < .05; Δ ≤ 21.7 μm) or similar trueness compared to stone models. Asiga dies demonstrated similar and NextDent significantly lower marginal trueness than IOS (P < .05; Δ ≤ 57.3 μm). Most AM margin areas had significantly lower trueness than stone (P < .001; Δ ≤ 57.2 μm). Asiga outperformed NextDent (P < .001). Shoulder trueness surpassed chamfer in optical scans (P = .01). Finish line design and gingiva location did not have a significant impact on AM and stone models (P > .05). Combining IOS and AM achieves clinically acceptable crown die trueness for single molar teeth. The choice of AM device is critical, with Asiga outperforming NextDent. Finish-line design has an impact on optical scans. Finish-line design and marginal gingiva location have little effect on AM trueness.

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.

A Quality Prediction and Parameter Optimization Approach for Turbine Blade Multistage Manufacturing

As core components of an aircraft engine, turbine blades are featured by complex curved surface with strict precision requirements in multistage manufacturing processes (MMPs). Hence, reliable quality prediction and parameter optimization strategy on MMPs have long been in great demand. However, most techniques focus on the precision improving of single-stage single-product manufacturing systems; these improvements are difficult to implement in MMPs with coordinate transformations among multiple machines. In this article, we propose a noninvasive feature-based quality prediction and parameter optimization framework for high-precision MMPs. In particular, rather than retrofitting sensors onto machinery after installation, this study presents an executable and noninvasive solution by using coordinate measuring machine (CMM) data as input features for prediction. Based on features of different stages of machining, a sequential multistep deep learning architecture is developed to predict the final product quality. A preheating optimization algorithm, modified from a local gradient search method, is used for the optimization of key initial machining features, which results are further improved by the L-BFGS method, thus increasing the final production quality. To estimate the effectiveness of the proposed framework, experiments are carried out on two series of aviation turbine blades with complex curved surfaces from the Wuxi Turbine Blade Company Ltd. China. CMM data at key stages (i.e., blade root milling and comprehensive accurate milling) are used as inputs to predict the final geometrical errors. Comparison results verify that the proposed framework achieves the smallest root mean square error at 0.030 mm and 0.032 mm for two blades, respectively.

Evaluation with a Coordinate-Measuring Machine of Dimensional Accuracy of the Abutment Duplication Technique in Cement- Retained Implant Restoration.

To evaluate the effectiveness and accuracy of a proposed duplication technique in terms of one- and three-dimensional discrepancies between an original abutment and polyurethane duplicates obtained through a conventional workflow in single-implant rehabilitation. A titanium, shoulderless abutment was chosen for a single-implant cemented rehabilitation. The master cast was made using a plastic-based die system, and the implant portion was separated. The implant section was consecutively duplicated eight times using a manual technique with polyvinyl siloxane and unfilled polyurethane resin as impression and die materials. The duplicates were analyzed with a coordinate-measuring machine (SmartScope Flash 200, Optical Gaging Products): one- and three- dimensional discrepancies were determined for each duplicate on 20 analysis points (A to T) located on the abutment surface. Changes in the abutment radius were also calculated to estimate the effects on cement thicknesses. One-dimensional discrepancies were -0.5 Å} 61.2 μm, -6.6 Å} 39.7 μm, and -19.4 Å} 47.8 μm on the X, Y, and Z axes, respectively; three-dimensional variation was -66.4 Å} 60.1 μm. Friedman test showed no significant difference between duplicates' one-dimensional variations on X (P = .059), Y (P = .156), or Z (P = .223) axes; a significant difference was found regarding three-dimensional changes (P < .001). Dunn test showed higher discrepancies on the X axis and on the abutment head. Mean variation of the abutment radius was -12.09 μm. The abutment duplication technique was shown to be an accurate and repeatable procedure for single cementable restorations.

A smooth surface measurement method by flexible contact using multiple fingers device

Contact measurement technology is commonly used for analysis and modeling of three-dimensional (3D) object. This paper presents a contact measurement method, using a claw type probe based on a set of rotary encoders that can flexibly contact objects with efficiently multi-lines scanning. In this paper, a 3D measurement system by flexible contact of multiple fingers was built. The claw probe was set on a coordinate measurement machine. By moving the position of the claw for interpolation detection to improve the sampling rate, higher precision 3D reconstruction was achieved. Also, a compensation algorithm was proposed for this type detector to improve measuring accuracy. In the experiments, two surface models were produced by 3D printing as the test objects. By comparing the designed surface with the reconstructed surface, it is demonstrated that this system can effectively and softly measure smooth surface, like the back of human body, which is valuable for further study and use in rehabilitation massage, apparel design, and etc.

Repositioning accuracy of the implant- and abutment-level prosthetic components used in conventional and digital workflows

ObjectivesTo evaluate the repositioning accuracy of the implant- and abutment-level impression components (impression abutments and implant scan bodies) and implant abutments (with and without anti-rotational hex index); also, to estimate the tightening torque influence on the positional stability of abutments. MethodsSeven types of prosthetic components (n = 7) [impression pick-up copings (PC), implant scan bodies (ISB), non‑hex and hex titanium base implant abutments (TB H and TB NH), multi-unit impression copings (MU PC), multi-unit implant scan bodies (MU ISB), and multi-unit caps (MU C) (Medentika GmbH)] were tested. For repositioning accuracy tests a coordinate measuring machine (CMM) was used. During assembly 15 Ncm torque for all components was applied. After measurement, only hex and non‑hex abutments were torqued to 25 Ncm and their coordinates were again recorded to assess torque influence. The procedure was repeated 7 times for each component. Linear and 3D deviations, angulation to the vertical axis, and axial rotation were calculated. The Kruskal-Wallis test was used to compare the measurements between the groups. A post-hoc test (Mann–Whitney U test) was used for pairwise comparison to determine the influence of the torque (α=0.05). ResultsImplant- and abutment-level components used for digital scans showed different positional discrepancies compared to ones used for conventional impressions and ranged from 10 to 37 µm. Hex abutments demonstrated statistically significantly lower 3D deviations (4.4 ± 7.1 µm) compared to non‑hex abutments (8.7 ± 6.1 µm). Torque influence was significantly lower for hex abutments than for non‑hex abutments. ConclusionsRepositioning inaccuracies were found in all implant- and abutment-level impression components (impression abutments and implant scan bodies) and all abutments (with and without anti-rotational hex index) tested. Final tightening of the components could cause further positional discrepancies. Clinical significanceThe misfit of the prosthetic components used in conventional and digital workflows stays in the clinically acceptable range. Even when multiple connections and disconnections on the track of the laboratory preparation is needed, it should not have a negative influence for single teeth reconstructions. However, in the complex cases with multiple implants, repetitive repositioning of the prosthetic components may lead to the accumulation of vertical, horizontal and rotational errors leading to the clinical problems with the passive fit of the final framework.

A Method for Measuring Shaft Diameter Based on Light Stripe Image Enhancement.

When the workpiece surface exhibits strong reflectivity, it becomes challenging to obtain accurate key measurements using non-contact, visual measurement techniques due to poor image quality. In this paper, we propose a high-precision measurement method shaft diameter based on an enhanced quality stripe image. By capturing two stripe images with different exposure times, we leverage their different characteristics. The results extracted from the low-exposure image are used to perform grayscale correction on the high-exposure image, improving the distribution of stripe grayscale and resulting in more accurate extraction results for the center points. The incorporation of different measurement positions and angles further enhanced measurement precision and robustness. Additionally, ellipse fitting is employed to derive shaft diameter. This method was applied to the profiles of different cross-sections and angles within the same shaft segment. To reduce the shape error of the shaft measurement, the average of these measurements was taken as the estimate of the average diameter for the shaft segment. In the experiments, the average shaft diameters determined by averaging elliptical estimations were compared with shaft diameters obtained using a coordinate measuring machine (CMM) the maximum error and the minimum error were respectively 18 μm and 7 μm; the average error was 11 μm; and the root mean squared error of the multiple measurement results was 10.98 μm. The measurement accuracy achieved is six times higher than that obtained from the unprocessed stripe images.

Enhance students’ engineering ability based on virtual three coordinate design and measurement

The three coordinate measuring machine (CMM) are increasingly widely used, but because of their high price, not easy to portable and other drawbacks, it is difficult to be widely used in university teaching procedures. Therefore, some disciplines such as measurement and control theories, measurement methods behind of the CMM are hard to well understood, which require students to have strong engineering ability. In order to solve the problem, the paper presents a virtual CMM way to improve the students engineering experience that improve the quality of course teaching as an assist tool. Firstly, use 3ds Max to model CMM, including probe, guide rail, frame, etc. Secondly,after the modeling development is completed, Hololens is used as a platform to develop scene interaction functions using Unity and c# scripts, that is, the connection between virtual scenes and students.Thirdly, in the virtual interface, students control the probe by the button to record and measure the coordinates of the object to be measured, and complete the measurement experiment. Students can master the measuring principle and measuring process of CMM faster through Hololens. So that students have a more intuitive understanding of CMM and are no longer limited by the traditional CMM teaching, it is of great significance to the cultivation of students’ engineering ability.

Structured-light 3D Scanning Performance in Offline and In-process Measurement of 3D Printed Parts

This paper presents a geometric analysis comparison of structured-light 3D scanners against coordinate measuring machines (CMMs) in measuring 3D printed plastic parts. The resulting geometric analysis of a 3D printed part measured with a contact probe on a CMM and measured with a structured light 3D scanner is presented, along with an error analysis that includes a statistical comparison of the measured geometric deviation. This analysis is then used to determine if structured-light 3D scanners are reliable enough to perform a GD&T analysis of specific features. This paper also presents the results of in-process 3D scanning and compares them to offline 3D scanning to determine the suitability of in-process 3D scanning for comprehensive analysis of geometric deviation and GD&T features.

Data-driven Model for CMM Probe Calibration to Enhance Efficiency and Sustainability

Ensuring precise measurement is critical for manufacturing industries; and a coordinate measuring machine (CMM) is widely used for automated inspection of critical and complex components. But there is a lack of clarity regarding optimal timepoint for CMM probe re-calibration. Too frequent calibrations increase the cost and an uncalibrated CMM probe affects the inspection quality. When to get a CMM probe calibrated is still an open question. It is important to accurately determine the optimal probe re-calibration intervals to mitigate the adverse effects on the quality and the time. This paper presents a novel data-driven approach to predict the optimal timepoint to re-calibrate a CMM probe. The data is collected at various levels to develop, train, and validate the predictive model, which includes numerical and categorical data-frame such as probe usage metrics, probe calibration environmental condition, probe specifications, workpiece data, probe calibrated dimension data and calibration requirement. The research potentially aims to reduce the CMM downtime without compromising the product quality variations that arise from the anomalies/errors related to the probe re-calibration thereby enhancing the inspection efficiency as well as sustainability.

Prediction of machining errors for free-form surfaces based on an improved grey model (1,N)

An improved grey model (GM) for predicting free-form surface machining errors was established to address the low measuring efficiencies of coordinate measuring machines (CMMs) and the low prediction accuracy of the GM(1,1) model. A number of points on a free-form surface are measured with a CMM, and machining errors are obtained. Ideas from metabolic methods and the GM(1,N) prediction model were combined. To reduce the impact of random fluctuations of the machining errors, a Markov prediction model was then used to correct the fitted results for the residuals and obtain the predicted results of the machining errors for free-form surfaces, thus improving the prediction accuracy of the model. The predicted results of the metabolic GM(1,1) and metabolic GM(1,N) models were then compared. The experimental results showed that the combination of metabolic theory, a grey model, and Markov theory effectively improved the prediction accuracy.

Laser Scanner-Based Robotic Coordinate Measuring Machine

The objectives of the research presented in this paper are to design, integrate and demonstrate a robotic Coordinate Measuring Machine (CMM) for digitizing 3D geometries of objects to be used in reverse-engineering applications. The paper describes the mathematical model, the integration of the light detection and ranging (LiDAR) sensor with the automated positioning system and the programming used to attain the technology. The digital reconstruction of an object’s 3D model is achieved by applying forward robot kinematics along with homogeneous transforms to the point cloud detected by the LiDAR. The object’s geometric features are determined using 2nd-order polynomial best fitted curves of the scanned point clouds using the bisquare fit method. The CMM uses forward robot kinematics along with homogeneous transforms to programmatically compensate for geometric positioning errors resulting from deviations in position and orientation of the CMM components during assembly and from deviations in position and orientation of the workpiece when it is located in its mounting device. The instrument is shown to reconstruct with remarkable qualitative accuracy the 3D model of a turbine blade. Using a better-quality detecting sensor, the instrument can be used as well in automated quality control and inspection applications.

The Manufacturing Processes of Airbus A320 Landing Gear Bhushings Using Reverse Engineering Methods

The aviation sector is currently enjoying fast growth, as seen by the manufacture of 8,650 Airbus A320 aircraft. One critical component is the landing gear bushing (P/N 201160616), which provides safety and performance during takeoff and landing. PT. GMF AeroAsiaTbk is having difficulty obtaining these bushings due to low stock, configuration changes, and delivery delays. To address this, PT. GMF AeroAsiaTbk, through PMA Holder GMF Aero Asia, intends to produce bushings independently under the Parts Manufacturing Approval procedure outlined in CASR Part 21 Sub-Part K, with DGCA monitoring. Reverse engineering approaches are utilized to overcome technical information restrictions, allowing high-quality bushings to be produced. The research goals are to collect dimensional and material data, develop optimal production methods, and understand the electroplating process on bushings. The reverse engineering procedure entails taking measurements with a vernier calliper and a Coordinate Measuring Machine (CMM) as well as reviewing the Component Maintenance Manual. Preparation, fabrication, inspection, packing, and marking are all part of the production process. Bright cadmium electroplating is used to prevent corrosion and enhance appearance. The findings are expected to improve production efficiency, decrease downtime, and ensure the availability of dependable spare parts.

Kinematic Calibration of an Industrial Manipulator without External Measurement Devices

This paper presents a practical approach to fully automated kinematic calibration of an industrial manipulator. The approach is based on the principle of plane constraint. The electrical signal is used to fix the moment of contact between the conductive tool and the flat surface. The measurement data are manipulator configurations (joint angles) at the moment of contact. A modification of the algorithm to deal with the scaling problem is also proposed. This approach provides both high calibration accuracy and lower cost of the experimental setup compared to coordinate measuring machines (CMMs), laser trackers, and vision systems. The article examines the impact of various methods of kinematic parameterization of manipulators: the Denavit – Hartenberg agreement (DH), product of exponentials (POE), as well as the complete and parametrically continuous model (CPC) on the calibration accuracy. A comparison is made of the open-loop and the proposed closed-loop calibration methods on the Puma 560 model known in the literature. POE parameters were converted to DH and CPC to compare accuracy after calibration based on these parameterizations. The method of computing POE-CPC transformation as a solution to a certain optimization problem is proposed. The problem of identifying geometric parameters in the presence of restrictions is solved by gradient optimization methods. Experiments have been carried out on an ABB IRB 1600 industrial manipulator with an installed conductive probe and an ABB IRBP A-500 robotic positioner with a conductive metal flat surface. A technique for indirectly checking the accuracy of calibration of kinematic parameters is proposed based on a study of the accuracy of manipulation when using these parameters.

Development of an on-machine surface measurement system for an ultra-precision five-axis machine

Ever-increasing demand for complex freeform surfaces machined by ultra-precision five-axis machines necessitates efficient on-machine surface measurement (OMSM) systems. While OMSM offers significant advantages in metrology efficiency and machining accuracy, integrating it with these machines presents a challenge due to complex data synchronization and processing. This paper addresses this challenge by proposing a dedicated controller for synchronized acquisition of sensor measurement data and machine coordinate data. Additionally, a straightforward sensor alignment method is presented. The effectiveness of the proposed OMSM system is demonstrated through successful 2D and 3D measurements, significantly streamlining the traditional time-consuming offline coordinate measuring machine (CMM) and optical profilometer measurements.

Study of the probe positioning accuracy of a coordinate measurement machine on uneven surface

Study of the probe positioning accuracy of a coordinate measurement machine on uneven surface

Global and Local Geometrical Imperfections of Pultruded GFRP Profiles Based on a Modal Approach

The ultimate capacity of pultruded glass fibre reinforced polymer (pGFRP) profiles depends significantly on geometrical imperfections (GIs), given their sensitivity to buckling phenomena arising from both thin walls and low elastic moduli. However, GIs are not yet comprehensively addressed in design guidance. This paper proposes a new approach to characterize the initial GIs of pGFRP profiles based on a modal approach. Given the lack of comprehensive knowledge in this area, this study presents a highly accurate and robust methodology to measure GIs and dimensional deviations (DDs) in pGFRP profiles using a 3D contact coordinate measurement machine (CMM). The modal approach encompasses the measurement of dimensional parameters and a point cloud transformation that enables the assessment of GIs associated with pure buckling modes of pGFRP profiles. This procedure allows the quantification of three types of global GIs associated to (i) minor-axis (weak axis), (ii) major-axis (strong axis) bending, and (iii) twist. Additionally, the procedure also includes the assessment of local GIs, considering the wall (plate-like) imperfections. The separation of GIs into these four types (shape and amplitude) is of major relevance as its paves the way to the development of analytical design formulas for the strength prediction of pGFRP members. The approach described in this paper also serves two important purposes: (i) the statistical analysis of DDs and GIs of pGFRP members, and (ii) the identification of distinct shapes and amplitudes of GIs that form the basis for reliable design considerations of pGFRP members.