How Geometrical Tolerances Affect the Measurement of Reciprocal Alignment of Two Different Assemblies: A Case Study

2010 ◽  
Author(s):  
David Vetturi ◽  
Matteo Lancini ◽  
Ileana Bodini
Keyword(s):  
Numerical Simulations ◽  
Angular Displacement ◽  
European Space Agency ◽  
Coordinate Measuring Machine ◽  
Linear Displacement ◽  
Repeated Measurements ◽  
Uncertainty Sources ◽  
Component Design ◽  
Measuring Machine ◽  
The Right

Often a designer has the problem to apply a suitable system of geometrical and dimensional tolerances to an assembly. The right solution is not unique, in fact it depends on the chosen parameters. If the tolerances have to be optimized, some important parameters have to be taken into account, e.g. the efficiency of each prescription, or if this last is reachable, or it can be verified and how much the realization costs. The authors opinion is that a statistical approach based on the Monte Carlo Method is very useful when the tolerances chains are complex. This paper shows an application of this method in order to verify the functional alignment between two assemblies and a critical analysis of the uncertainty in phase both of the component design and test. This study has been developed thanks to the strict requirements imposed by ESA (European Space Agency) on the components that Thales Alenia Space has to realize within the LISA Pathfinder experiment. The very critical aspect of this work is to reciprocally align two cylindrical elements of two different assemblies. The specifications require 100 μm as maximum linear displacement and 300 μrad as maximum angular displacement. Moreover this prescriptions have to be verified also when the two elements are independently moving. To be able to reach such strict accuracy level the components have been assembled in an ISO 100 class cleanroom and the work space was a 3D Coordinate-Measuring Machine (CMM). The cylindrical elements have a 10 mm diameter, so the value of the measurement uncertainty associated with the alignment check is fundamental. Starting from the different uncertainty sources, the measurability and verifiability of the alignment have been considered and evaluated. The overall uncertainty has been assessed by numerical simulations which have taken into account the dimensional, geometrical and form tolerances as well as the instrumental uncertainty of the 3D CMM. This estimation has been positively validated by a session of repeated measurements. Numerical simulations have also allowed performing a sensitivity analysis, in order to give information about which sources more contribute to the overall uncertainty.

scholarly journals Information Contents of a Signal at Repeated Positioning Measurements of the Coordinate Measuring Machine (CMM) by Laser Interferometer

2016 ◽  
Vol 16 (5) ◽  
pp. 273-279 ◽  
Author(s):  
Tomáš Stejskal ◽  
Tatiana Kelemenová ◽  
Miroslav Dovica ◽  
Peter Demeč ◽  
Miroslav Štofa
Keyword(s):  
Permanent Deformation ◽  
Coordinate Measuring Machine ◽  
Repeated Measurements ◽  
Time Interval ◽  
Passive Resistance ◽  
Complex Information ◽  
Wear And Tear ◽  
Measuring Machine ◽  
The Moment ◽  
Spatial Positioning

Abstract The input of this paper lies in displaying possibilities how to determine the condition of a coordinate measuring machine (CMM) based on a large number of repeated measurements. The number of repeated measurements exceeds common requirements for determining positioning accuracy. The total offset in the accuracy of spatial positioning consists of partial inaccuracies of individual axes. 6 basic errors may be defined at each axis. In a triaxial set, that translates into 18 errors, to which an offset from the perpendicularity between the axial pairs must be added. Therefore, the combined number of errors in a single position is 21. These errors are systemic and stem from the machine’s geometry. In addition, there are accidental errors to account for as well. Accidental errors can be attributed to vibrations, mass inertness, passive resistance, and in part to fluctuations in temperature. A peculiar set of systemic errors are time-varying errors. The nature of those errors may be reversible, for instance if they result from influence of temperature or elastic deformation. They can be also irreversible, for example as a result of wear and tear or line clogging, due to loosened connection or permanent deformation of a part post collision. A demonstration of thermal equalizing of the machine’s parts may also be observed in case of failure to adhere to a sufficient time interval from the moment the air-conditioning is turned on. Repeated measurements done on a selected axis with linear interferometer can provide complex information on the CMM condition and also on the machine’s interaction with the given technical environment.

Modeling and Calibration of the Orthogonality Deviation between the "X" and "Y" Axes of Coordinate Measuring Machines

2018 ◽  
Vol 875 ◽  
pp. 84-88
Author(s):  
César Augusto Galvão de Morais ◽  
Marilia da Silva Bertolini ◽  
Benedito di Giacomo
Keyword(s):  
Mathematical Modeling ◽  
Coordinate Measuring Machine ◽  
Displacement Transducer ◽  
Linear Displacement ◽  
Calibration Data ◽  
Correct Operation ◽  
Compensation Plans ◽  
Main Plane ◽  
Productive Process ◽  
Measuring Machine

The increase of the quality in a productive process allows reduction of costs besides adding value to the product. When manufacturing a product within the tolerances specified in the design it is possible to obtain a correct operation of this product, ensuring the minimum time of use and with a lower risk of early failure. In this sense, machines and equipments involved in the manufacturing and inspection processes must also maintain an acceptable quality of operation by knowing the errors present in the machine structure through the calibration, such as errors due to lack of orthogonality between the axes, caused by inaccurate assemblies. The calibration errors in these machines allow elaborate error compensation plans and thus improve the rate of flawless products in production. The objective of this paper was to identify the influence of errors due to a lack of orthogonality in a bridge type coordinate measuring machine (CMM) through calibration and mathematical modeling of errors. Error calibration is performed with a linear displacement transducer, a granite square and a set support brackets for the granite square. By means of the calibration data and the mathematical modeling of the orthogonality deviation an influence of the measured deviation on the "X" and "Y" directions of the CMM is obtained. The error due to the lack of orthogonality between the "X" and "Y" axes of the CMM was approximately 8.9558 negative arcoseg; in this way, it is evidenced that the angle formed between these axes is 89.9975°. Through this study it can be concluded that orthogonality deviation in the main plane of the machine produces negative components for the axes "X" and "Y", with higher influence on the points collected as it away from machine scales, making greater the error intensity on the results of measurements made at positions farthest from the "X" and "Y" scales.

Fixture Design Process Automation for Coordinate Measuring Machines: A Knowledge-Based Approach

2006 ◽  
Vol 526 ◽  
pp. 103-108
Author(s):  
J. Perez ◽  
R. Hunter ◽  
J.C. Hernandez ◽  
Antonio Vizan Idoipe
Keyword(s):  
Design Process ◽  
Manufacturing Process ◽  
Coordinate Measuring Machine ◽  
Fixture Design ◽  
Knowledge Based ◽  
Design And Manufacturing ◽  
Inspection Process ◽  
Measuring Machine ◽  
The Right ◽  
Inspection Fixture

Nowadays, the inspection process is an essential part of the manufacturing process, where a product is subjected to verification of the geometric features, dimensions and tolerance specifications with respect to the product design specifications. One of the most interesting topics in the automation of the inspection process is the right fixture design. In the fixture design process we have used the information provided by the part design and manufacturing process. However, the lack of integration and structuring of this information results in one of the most important problems, producing an increase in the time and cost implied in the development of the fixture design and its implementation. For this reason, this work presents a knowledge model for the inspection fixture design process for a Coordinate Measuring Machine (CMM), which allows the automation of the inspection fixture design process to be made easier, reducing time and cost associated to the inspection process and to the manufacturing process in general.

CMM Measurement Uncertainty Reduction via Sampling Strategy Optimization

2008 ◽  
Author(s):  
Giovanni Moroni ◽  
Stefano Petro`
Keyword(s):  
Measurement Uncertainty ◽  
Measurement Errors ◽  
Coordinate Measuring Machine ◽  
Sampling Strategy ◽  
Uncertainty Reduction ◽  
Repeated Measurements ◽  
Trade Off ◽  
Geometrical Error ◽  
Measuring Machine

Uncertainty is a key concept in any environment which involves measurements to ensure process quality: a trade-off has to be found between measurement costs, which increase as uncertainty lowers, and costs related to measurement errors. In mechanics, geometrical conformance is a common requirement. Two similar standards series deal with the problem of uncertainty in geometrical error estimate: ASME B89.7.3 and ISO 14253. Geometrical inspection is often performed by means of a “Coordinate Measuring Machine” (CMM). For a CMM, a trade off between measurement and errors costs may be found by optimizing the sampling strategy. In this work a cost function will be proposed as support for finding a trade-off between measurement uncertainty and costs. This function may be optimized by means of an heuristic algorithm. The method will involve repeated measurements of calibrated parts to evaluate uncertainty (like in ISO/TS 15330-3). A case study will be proposed.

scholarly journals A Large Range Linear Displacement Calibration System Based on Coordinate Measurement and Laser Interference

2018 ◽  
Vol 232 ◽  
pp. 02016 ◽  
Author(s):  
Zhihua Jiang ◽  
Yanhua Zeng ◽  
Zhenglong Cai
Keyword(s):  
Large Range ◽  
Coordinate Measuring Machine ◽  
Linear Displacement ◽  
Displacement Sensor ◽  
Dual Frequency ◽  
Calibration System ◽  
Laser Interference ◽  
Coordinate Measurement ◽  
Measuring Machine ◽  
Frequency Laser

The linear displacement sensor is widely used in industrial measurement. The linear displacement sensor with measuring range less than 200mm is usually measured on a universal length measuring instrument. There is no good method to calibrate linear displacement sensor with measuring range larger than 200mm. The calibration system of linear displacement based on coordinate measurement and dual frequency laser interference is developed. The guide rail and measuring positioning system of coordinate measuring machine is used. The sampling signal of dual frequency laser interferometer is connected with the pulse signal triggered by coordinate measuring machine. The accurate position information of the linear displacement sensor is obtained and processed by industrial computer. According to JJF 1305-2011 Calibration Specification for Linear Displacement Sensor, a large range of linear displacement sensors is calibrated. The accuracy and reliability of linear displacement calibration system based on coordinate measurement and laser interference is verified.

Three-Dimensional Accuracy of Implant and Abutment Level Impression Techniques: Effect on Marginal Discrepancy

2011 ◽  
Vol 37 (6) ◽  
pp. 649-657 ◽  
Author(s):  
Marzieh Alikhasi ◽  
Hakimeh Siadat ◽  
Abbas Monzavi ◽  
Fatemeh Momen-Heravi
Keyword(s):  
Angular Displacement ◽  
Angular Position ◽  
Three Dimensional ◽  
Coordinate Measuring Machine ◽  
Dimensional Accuracy ◽  
Acrylic Resin ◽  
Positional Accuracy ◽  
Type Iv ◽  
Marginal Discrepancy ◽  
Measuring Machine

Impression techniques should precisely represent the 3-dimensional status of implants to allow for the fabrication of passively fitting prostheses and subsequently the elimination of strain on supporting implant components and surrounding bone. The aim of this study was to compare the accuracy of an abutment level impression method with that of an implant level (direct and indirect) impression method using polyether impression material to obtain precise definitive casts and prostheses. A reference acrylic resin dentoform with 2 internal connection implants (Implantium) was made. A total of 21 medium-consistency polyether impressions of the dentoform, including 7 direct implant level, 7 indirect implant level, and 7 abutment level (after 2 straight abutments were secured), were made. Impressions were poured with American Dental Association (ADA) type IV stone, and the positional accuracy of the implant replica heads and abutment analogs in each dimension of x-, y-, and z-axes, as well as angular displacement (Δθ), was evaluated using a coordinate measuring machine. Noble alloy 3-unit castings were fabricated and seated on the abutments in 3 groups; marginal discrepancies were measured at 4 points between prostheses and abutments. Data were analyzed using Mann-Whitney U test, 1-way analysis of variance (ANOVA), and Kruskal-Wallis tests. In comparisons of different impression techniques, only significant statistical Δθ differences were noted between the abutment level method and other techniques (P < .001). Results of this study reveal that although the implant level impression method could better transfer the angular position of the implants (Δθ), the impression method could not affect Δy, Δx, and Δz coordinates of the implants or marginal discrepancy of the 3-unit fixed partial dentures (FPD).

scholarly journals Evaluation of dimensional accuracy of dental bridges manufactured with conventional casting technique and CAD/CAM system with Ceramill Sintron blocks using CMM

2018 ◽  
Vol 12 (4) ◽  
pp. 264-271 ◽  
Author(s):  
Alireza Izadi ◽  
Fariborz Vafaee ◽  
Arash Shishehian ◽  
Ghodratollah Roshanaei ◽  
Behzad Fathi Afkari
Keyword(s):  
Reference Model ◽  
Coordinate Measuring Machine ◽  
Dimensional Accuracy ◽  
Three Dimensions ◽  
Casting Technique ◽  
Dimensional Changes ◽  
Conventional Casting ◽  
Cad Cam ◽  
Milling Method ◽  
Measuring Machine

Background. Recently, non-presintered chromium-cobalt (Cr-Co) blocks with the commercial name of Ceramill Sintron were introduced to the market. However, comprehensive studies on the dimensional accuracy and fit of multi-unit frameworks made of these blocks using the coordinate measuring machine (CMM) are lacking. This study aimed to assess and compare the dimensional changes and fit of conventional casting and milled frameworks using Ceramill Sintron. Methods. A metal model was designed and scanned and 5-unit frameworks were fabricated using two techniques: (I) the conventional casting method (n=20): the wax model was designed, milled in the CAD/CAM machine, flasked and invested; (II) the milling method using Ceramill Sintron blocks (n=20): the wax patterns of group 1 were used; Ceramill Sintron blocks were milled and sintered. Measurements were made on the original reference model and the fabricated frameworks using the CMM in all the three spatial dimensions, and dimensional changes were recorded in a checklist. Data were analyzed with descriptive statistics, and the two groups were compared using one-way ANOVA and Tukey test (α=0.05). Results. The fabricated frameworks in both groups showed significant dimensional changes in all the three dimensions. Comparison of dimensional changes between the two groups revealed no significant differences (P>0.05) except for transverse changes (arch) that were significantly greater in Ceramill Sintron frameworks (P<0.05). Conclusion. The two manufacturing processes were the same regarding dimensional changes and the magnitude of marginal gaps and both processes resulted in significant dimensional changes in frameworks. Ceramill Sintron frameworks showed significantly greater transverse changes than the conventional frameworks.

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