Tolerance Verification Research Articles

A High-Performance Quadruple-Node-Upset-Tolerant Latch Design and an Algorithm for Tolerance Verification of Hardened Latches

A High-Performance Quadruple-Node-Upset-Tolerant Latch Design and an Algorithm for Tolerance Verification of Hardened Latches

A simulation methodology for verification of transient fault tolerance of ASICs designed for high-energy physics experiments

Transient fault tolerance verification is a crucial step in the design of radiation-tolerant ASICs for high-energy physics experiments. In this paper, we discuss a methodical approach toward the verification of transient fault tolerance of ASICs using industry-standard methodologies and tools. The framework for fault verification includes tools for fault enumeration, fault injection, and running fault campaigns. The framework supports fault verification at various levels of design abstraction from high-level register-transfer model to gate-level netlist. The methodology and framework described in this paper were successfully used to identify SEE vulnerabilities in various ASICs designed at CERN.

Influence of workpiece tolerances on the fixtures design. Case study

The tolerances of a part influence both the operation of the assembly of which it is part and the technological manufacturing process. High tolerances can lead to an assembly that does not work at the designed parameters, and low tolerances require additional machining operations that increase the cost of the part. The manufacturing series is another factor that influences the technological process. Large series production requires special facilities in terms of processing and control equipment which are needed in the manufacturing process. The paper presents a case study on the influence of tolerances of a part being produced in large series on the construction of the orientation and clamping device used in machining. Starting from the dimensions indicated in the design drawing, a first version of the fixture is proposed in which the parts are fixed and the tolerance of the closing dimension of the assembly of parts is analysed using the Worst Case and Root-Sum-Square methods. Since the closure size tolerance is outside the recommended range, another variant of orientation and fixture is proposed. By re-analysing, the closing dimension tolerance by the two methods mentioned above it was confirmed the necessity of modifying the part width tolerance. The analysis of the tolerance of the closing quota is resumed by the two methods mentioned above and the result confirms that it is necessary to change the tolerance to the width of the piece. The tolerance verification of the closure dimension of the assembly formed by the parts fixed in the device is performed by Monte Carlo simulation.

Elastic–Plastic Fracture Mechanics Guidance and Analysis Validation

Damage tolerance is an important consideration in space structures applications. However, many space and launch vehicle components experience large cyclic stresses and cannot be evaluated using linear elastic fracture mechanics (LEFM). In these instances, elastic–plastic fracture mechanics (EPFM) can be used in the damage tolerance verification process. This paper provides practical guidance on the use of LEFM and EPFM as they relate to space structures. The limitations of LEFM-based approaches to damage tolerance verification are explored, demonstrating that inappropriate application of LEFM can be unconservative. Criteria are provided to help the engineer determine if EPFM analysis is required for a given scenario. Finally, a practical method of EPFM-based damage tolerance analysis is introduced and validated against test data from several test campaigns with excellent correlation to experimental data.

Improving Observations of Precipitation Type at the Surface: A 5-year Verification of a Radar-derived Product from the United Kingdom Met Office.

AbstractThis study aims to verify the skill of a radar-based surface precipitation type (SPT) product with observations on the ground. Social and economic impacts can occur from SPT because it is not well forecast or observed. Observations from the United Kingdom Meteorological Office’s weather radar network are combined with post-processed numerical weather prediction (NWP) freezing level heights in a Boolean logic algorithm to create a 1 km resolution cartesian-gridded map of SPT. Here 5 years of discrete non-probabilistic outputs of rain, mixed phase, and snow are compared against surface observations made by trained observers, automatic weather stations, and laser disdrometers. The novel skill verification method developed as part of this study employs several tolerances of space and time from the SPT product, indicating the precision of the product for a desired accuracy. In general the results indicate that the tolerance verification method works well and produces reasonable statistical score ranges grounded in physical constraints. Using this method, we find that the mixed precipitation class is the least well diagnosed which is due to a negative bias in the input temperature height field, resulting in rain events frequently being classified as mixed. Snowis capturedwell by the product which is entirely reliant upon a post-processed NWP temperature field, although a single period of anomalously cold temperatures positively skewed snow scores with low-skill events. Furthermore, we conclude that more verification consistency is needed amongst studies to help identify successful approaches and thus improve SPT forecasts.

Model-based measurement of internal geometry of solid parts with sub-PSF accuracy using laser-ultrasonic imaging

The problem of workpiece tolerance verification is of high interest in the field of nondestructive testing and evaluation. In this paper, reflection mode immersion 2D laser-ultrasound tomography is proposed for control of dimensions of solid objects with piecewise linear surface profiles. Pulsed laser radiation is used for generation of short ultrasonic probe pulse providing high spatial resolution. Wideband array of piezofilm sensors is used for detection of the waves reflected by the external and internal surfaces of the object. The image reconstruction algorithm accounts for refraction of acoustic waves at the liquid-solid interface. The contrast-enhanced reconstructed image is processed using the virtual model of the inspected part and the least-squares method to measure its actual dimensions. The accuracy obtained in the experiments with PMMA and duralumin samples is better than 100 μm in axial direction and is better than the size of the point-spread function in the material of the inspected part.

Proposition and experimental evaluation of a point-based compensation approach to reduce systematic errors in CT measurements

Industrial applications of computed tomography (CT) for dimensional metrology have increased steadily over the last few years, despite the fact that the measurement uncertainty has rarely been evaluated and reported. Despite being an important prerequisite of any scientific or industrial measurement, the complex CT measurement chain and the numerous influencing quantities involved in the measurement process mean that the problem of evaluating the uncertainty and tracing the dimensional measurement results back to the unit of length remains an unsolved issue. In this paper, the use of master part reference measurements for later point-based compensation of CT datasets is proposed to correct known systematic effects and reduce the measurement uncertainty down to the level of the CT measurement process repeatability, for part features that can be accessed and calibrated using a reference coordinate measuring system (R-CMS). The point-based compensation approach is described, experimentally tested using a prismatic part and is discussed for several geometrical tolerance verification cases.

Geometric Tolerance Verification - Innovative Evaluation of Facade Surface Flatness Using TLS (Terrestrial Laser Scanning)

This article assesses the application of TLS when evaluating the façade surface flatness on finished facade. Current methods of geometrical tolerance verification are reviewed and the results are compared data obtained from point clouds (using TLS).The process of currently used methods consist of manual verification of flatness by spirit level in accordance with national standards, which specifies exact places to be assessed and the number of measurements. With TLS technology we assess the surface quality and flatness more precisely, faster and moreover, investigate 100% of area. This may lead to better evaluation of the relative position of investigated areas, points and constructions. However, a further investigation, which would define the methodology for evaluation the geometric tolerance from point clouds is needed.

Development of a library of feature fitting algorithms for CMMs

Conformance of a manufactured feature to the applied geometric tolerances is done by analyzing the point cloud that is measured on the feature. To that end, a geometric feature is fitted to the point cloud and the results are assessed to see whether the fitted feature lies within the specified tolerance limits or not. Coordinate Measuring Machines (CMMs) use feature fitting algorithms that incorporate least square estimates as a basis for obtaining minimum, maximum, and zone fits. However, it is well known that results obtained from different vendors for the same data set often do not agree. This may be because of different interpretations of the GD&T standards, or the use of least squares algorithms as the basis for all fitting. Therefore, a reference or normative comprehensive library of algorithms addressing the fitting procedure (all datums, targets) for every tolerance class is needed. The library is specific to feature fitting for tolerance verification. This paper addresses linear, planar, circular, and cylindrical features only. This set of algorithms described conforms to the international Standards for GD&T. In order to reduce the number of points to be analyzed, and to identify the possible candidate points for linear, circular and planar features, 2D and 3D convex hulls are used. For minimum, maximum, and Chebyshev cylinders, geometric search algorithms are used. Algorithms are divided into three major categories: least square, unconstrained, and constrained fits.

Optimal inspection strategy planning for geometric tolerance verification

Abstract Two features characterize a good inspection system: it is accurate, and compared to the manufacturing cost, it is not expensive. Unfortunately, few measuring systems posses both these characteristics, i.e. low uncertainty comes with a cost. But also high uncertainty comes with a cost, because measuring systems with high uncertainty tend to generate more inspection errors, which come with a cost. In the case of geometric inspection, the geometric deviation is evaluated from a cloud of points sampled on a part. Therefore, not only the measuring device has to be selected, but also the sampling strategy has to be planned, i.e. the sampling point cloud size and where points should be located on the feature to inspect have to be decided. When the measuring device is already available, as it often happens in geometric measurement, where most instruments are flexible, an unwise strategy planning can be the largest uncertainty contributor. In this work, a model for the evaluation of the overall inspection cost is proposed. The optimization of the model can lead to an optimal inspection strategy in economic sense. However, the model itself is based on uncertainty evaluation, in order to assess the impact of measurement error on inspection cost. Therefore, two methodologies for evaluating the uncertainty will be proposed. These methodologies will be focused on the evaluation of the contribution of the sampling strategy to the uncertainty. Finally, few case studies dealing with the inspection planning for a Coordinate Measuring Machine will be proposed.

Profile Tolerance Verification for Free-form Surfaces Using Medial Axis Transform

Tolerances for freeform surfaces are specified using profile tolerance that controls form or combination of size, form, orientation and location of a feature(s) relative to a true profile. Freeform surfaces are generally inspected by using fixtures on a coordinate measuring machine (CMM). The combination of fixtures and the CMM enables the establishment of correspondence between points on the machined and nominal surface for tolerance verification. To respond to the market quickly, it has become inevitable to use 3D scanners that can scan an object rapidly and provide dense unorganized points as an output without maintaining any correspondence with the nominal CAD model. Current state of art uses the shortest distance criterion to establish correspondence and verify the profile tolerances. This results in acceptance of parts that ought to be rejected and vice versa.A novel, alternative approach is proposed to overcome this deficiency and verify tolerances specified on a free-form surface. The technique establishes the correct one to one correspondence between the machined surface and CAD model using the Medial axis transform (MAT). The MAT of both the nominal surface and the measured points respectively, are discretised to obtain grids. Corresponding points on the two grids are then used to verify the deviation of the machined surface from the nominal surface. Results of preliminary experiments with simulated data are presented.

Computed Tomography as a Tool for Tolerance Verification of Industrial Parts

Computed tomography (CT) is becoming an important technology for industrial applications, enabling fast and accurate control of manufactured parts. In only a few minutes, a complete 3D model of a part may be obtained, allowing measurements of external and internal features. This paper presents results of tolerance verification of a plastic housing for an insulin pen manufactured by Novo Nordisk A/S. Calculation of measurement uncertainties was taken into account in decision making regarding the specified tolerance limits. Variables in terms of CT systems, data sets, and evaluation software are considered in this study.

AK-ILS: An Active learning method based on Kriging for the Inspection of Large Surfaces

Abstract Tolerance verification permits to check the product conformity and to verify assumptions made by the designer. For conformity assessment, the uncertainty associated with the values of the measurands must be known. In fact, to evaluate form characteristics of large aircraft structure workpieces, sampling is required, so a measurement error is present: exact estimation of form characteristics would require complete knowledge of the surface. To minimise this measurement error, this paper presents a Kriging-based procedure to identify the minimum of measured points to check the conformity with a given confidence level. The proposed method is validated on a simple example of orientation tolerance and then performed to inspect the form defect on three large aircraft workpieces.

Measurements and Characterization of Photovoltaic Modules for Tolerance Verification

One of the most important aspects of photovoltaic modules is reliability for future uses, that is, a certain module will last certain number of years in use (generally 30 or 35 years). Reliability yields from excellent qualification tests on photovoltaic (PV) modules. Testing for reliability identifies unknown failure mechanisms and whether modules are susceptible to known failure mechanisms. This paper illustrates techniques of outdoor measurements and qualification characterization to know PV module conditions for commercial uses. Matrix methods are used for energy prediction. Failure material tests, using digital imaging and thermography, have also been conducted.

A Predictive Model for Tolerance Verification of Bent Sheet Metal Parts

This paper presents a complete model including method and result for tolerance verification of bent sheet metal parts. The method uses a mathematical model to take into account aspects influencing the dimensional accuracy of linear and angular dimensions of bent parts. The model was implemented using a set of experimental data to estimate the dimensional accuracy for dimensions of interest of a specific part. Comparing the prediction data with the measured results allowed validation of the model.

Early cost estimation for tolerance verification

This paper presents a methodology for estimating the verification cost of geometric tolerances at the design stage, which is useful for optimizing the tolerance specifications of mechanical products. The tolerance verification cost may be seen as the sum of the measurement and uncertainty costs. The measurement cost depends on the adopted device and on the measurement time. The uncertainty cost is related to type A (declaring a conforming part non-conforming) and type B (declaring a non-conforming part conforming) errors: these errors are strongly influenced by the measurement procedure, which depends on the measurement device and determines the measurement time. The methodology is illustrated and validated using simulation and industrial case studies.

Medial Axis Transform for Tolerance Verification

AbstractMedial Axis Transformation (MAT) is proposed as an intermediate representation for tolerance verification. It is assumed that the manufactured part has been scanned and that points on the boundary are available as a dense cloud of points with respect to a single reference frame (Inspection Reference Frame, IRF) that is typical of most scanners in use today. Tolerance verification involves first locating the IRF with respect to the CAD reference frame (CRF) followed by verification as laid out according to appropriate standards. The former involves segmenting the point cloud and fitting surfaces to the segmented set of points. The use of MAT eliminates the need for both segmentation and surface fitting while enabling the verification of tolerances specified with respect to the datum. MAT also avoids the problem of rejection of parts within tolerances that arises in current practice due to the over estimation of the tolerance zone when using the least squares method or other optimization techniques ...

Computed tomography for dimensional metrology

The paper gives a survey of the upcoming use of X-ray computed tomography (CT) for dimensional quality control purposes: i.e. for traceable measurement of dimensions of technical (mechanical) components and for tolerance verification of such components. It describes the basic principles of CT metrology, putting emphasis on issues as accuracy, traceability to the unit of length (the meter) and measurement uncertainty. It provides a state of the art (anno 2011) and application examples, showing the aptitude of CT metrology to: (i) check internal dimensions that cannot be measured using traditional coordinate measuring machines and (ii) combine dimensional quality control with material quality control in one single quality inspection run.

Bisimulation conversion and verification procedure for goal-based control systems

Fault tolerance and safety verification of control systems are essential for the success of autonomous robotic systems. A control architecture called Mission Data System (MDS), developed at the Jet Propulsion Laboratory, addresses these needs with a goal-based control approach. In this paper, a software algorithm for converting goal network control systems into linear hybrid systems is described. The conversion process is a bisimulation; the resulting linear hybrid system can be verified for safety in the presence of failures using existing symbolic model checkers, and thus the original goal network is verified. A moderately complex example goal network control system is converted to a linear hybrid system using the automatic conversion software that is based on the bisimulation and then is verified.

Tolerance-based localization algorithm: form tolerance verification application

Current localization techniques have been successfully used for aligning sculptured surfaces with CAD models in inspection applications. However, tolerance specifications are not considered as an integral part of the localization process. The tolerance verification and comparison with measured surfaces occur at a later step to accept or reject the manufactured part. This two-step process prolongs the inspection time. For the first time, this paper presents a novel localization algorithm for inspection that integrates the tolerance specifications as an optimality criterion. A closed-form solution algorithm that applies 3D rigid body transformation using quaternion and uses a minimum acceptable deviation zone approach was developed. The formulation is based on the mathematical definitions from ANSI Y14.5.1 standards (American National Standard Institute) for form tolerances. The new iterative minimum acceptable deviation zone localization algorithm is formulated using four types of form tolerances: straightness of a median line, straightness of a surface line, flatness and cylindricity. It is applied and compared to several benchmark examples for validation. The results demonstrated the ability of the new localization approach to achieve comparable results but with less computation effort due to using a constraint satisfaction problem and a closed-form solution algorithm in the formulation. The merit of the new approach stems from its ability to increase the efficiency of tolerance verification during the inspection process. The applicability of the proposed algorithm to various types of tolerance is highlighted.