Flatness Tolerance Research Articles

FABRICATION OF FLEXIBLE FIELD-EFFECT TRANSISTORS ON 25 μm PEN FOIL

The development of high performance thin-film transistors on flexible plastic substrates is of great importance for the manufacturing and industrialization of flexible electronic devices, such as flexible displays. Here we present different approaches to fabricate bottom-gate field-effect transistors on 25 μm heat stabilized polyethylene naphthalate (PEN) foil using photolithography and solution processing. The flexibility and dimensional instability of the substrate constituted the main challenge during manufacturing. We developed a novel method to handle the foils during processing by reversibly attaching them onto 6 inch Si wafers. The so-called foil-on-carrier assembly showed excellent flatness (about 1 μm) and good dimensional stability and tolerance towards the different processing steps up to 160°C. Transistors were made either using an organic polymer or an inorganic oxide as gate dielectric material. Source and drain gold electrodes were patterned using standard photoresist patterning followed by wet etching, or by lift-off. The feature sizes in the transistors were downsized from 5 μm to sub-micrometer to improve the performance. In order to achieve structures with high resolution, all functional layers were patterned using a commercial wafer stepper (PAS5500/100D). The two dielectric materials used and the two ways of making the source-drain resulted in four different metal-insulator-metal (MIM) stacks. The MIM stacks were characterized by optical microscopy, scanning electron microscopy and four point resistance measurements. Registration accuracies below 0.5 μm were found over the whole wafer. Transistor fabrication was finished by depositing pentacene derivatives from solution.

無変形冷凍ピンチャックの開発（第２報）―ピン上への冷凍液塗布法と塗布特性―

Large quartz masks require a flatness tolerance of 10 μm to transfer fine patterns; however, these masks typically have a warp range of 10 to 100 μm. Fabricating a nonwarped mask is difficult because, during the polishing process, the mask substrate cannot be held without deformation. Therefore, a nondeforming freezing pin chuck has been developed. This paper describes a new application method and the resulting characteristics of the freezing liquid droplets. An oil-repellent coating and a newly developed low-speed spraying method were used to make a spherical droplet on a pin. The evaporation times of freezing liquid and water droplets on a 0.5-mm-diameter pin are the same (about 200 sec) despite the difference in volume, because the water droplet has a significantly larger surface area. After the oil-repellent coating was applied, the contact angle of the freezing liquid droplet increased from about 40° to about 120°, and the height increased from 65 to over 300 μm; likewise, the contact angle of the water droplet increased from about 130° to about 160°, and the height increased from 400 to over 1000 μm. When combined with the oil-repellent coating, the new low-speed spraying method yielded a freezing liquid droplet with a height of over 200 μm on a 0.5-mm-diameter pin — more than three times the height generated before the oil-repellent coating was applied.

Flatness, Cylindricity and Sphericity Assessment Based on the Seven Classes of Symmetry of the Surfaces

Dimensional inspection of a manufactured surface by means of a coordinate measuring machine (CMM) produces a set of Cartesian coordinates. The coordinates are processed to yield the geometric tolerance of the surface. This paper presents a new approach to the evaluation of flatness, cylindricity and sphericity tolerance based on surface invariance with regard to the rigid motions. The proposed algorithm transforms, through homogeneous transformation matrices, the coordinates measured to best fit the reference element of the surface class from which the actual measurements were sampled. The transformation matrix is simplified taking into account the invariance of the sum of the squared normal distances of the measured points from the nominal surface as regards some rigid motions. This invariance is a consequence of the invariance as regards some displacements of the nominal surface from which the data points were sampled. In this way, the number of parameters to be optimised is reduced in comparison with the six parameters characterizing the general homogeneous transform matrix. The methodology was computer implemented and numerical simulations were performed for planes, cylinders, and spheres in order to validate the effectiveness of the approach. The results indicate that the proposed algorithm provides accurate and quick assessments.

On the Generation of the Specification Surface Model of Planar Feature with Flatness

The new-generation standards of Geometrical Product Specifications (GPS) take the measurement and verification of manufactured parts according to the duality principle. The Specification Surface Model (SSM) is a simulation model of the actual manufactured part which plays a decisive role in the process of duality verification. The existing methods, however, have not been found to carry out much related research on the generation of SSM. This paper presents a method to generate the SSM for the characteristic of planar feature with flatness under the standards of GPS. The mathematical model of the flatness tolerance is firstly established. Secondly, in order to get the simulation points to simulate the actual characteristics of the manufactured parts, both of the functional requirements of the parts and the influences of the manufacturing process are considered. And then the simulation points under the normal distribution are generated within their tolerance zone by computer. By using the approximation method of the least-squares SSM is then obtained. Finally, an example is used to illustrate the proposed method.

An enhanced convex-hull edge method for flatness tolerance evaluation

Flatness is one of the elementary geometric forms to be tested for ensuring the acceptable quality of machined components. The minimum-zone evaluation problem for flatness is to determine the minimum tolerance zone enclosing all the points measured from a surface of the machined components. Although a variety of attempts has been made for the past two decades to solve the problem, methods guaranteeing an exact minimum-zone solution are very limited. One category of the exact methods is certainly the computational-geometry-based approaches such as the so-called convex-hull edge method. This paper presents a modified convex-hull edge method which significantly enhances its computational efficiency such that large-sized data sets with thousands of points can be solved within a negligible computation time using a personal computer. To test the validity of the method, a number of test data sets including those published in the literature and new large data sets generated in this paper were solved. The obtained solutions were compared with those produced by the existing methods. The results show the effectiveness, efficiency, and robustness of the method in that an exact minimum tolerance is always obtained for each of the test data sets solved in less than tens of CPU milliseconds.

Statistical Sampling Strategies for Geometric Tolerance Inspection by CMM

Bianca Maria Colosimo, Ester Gutierrez Moya, Giovanni Moroni andStefano Petr`oAbstract: More and more often, procedures for profile/surface monitoring and inspectionrefer to geometric specifications. In fact, the number of form tolerance requirements (such asstraightness, roundness, flatness, cylindricity, free-form profiles and surfaces) are increasinglyappearing in technical drawings. Usually, Coordinate Measuring Machines (CMMs) are usedto measure points on the specific feature under study in order to decide whether the machineditem is conforming to requirements. In fact, measured points are used to compute the formerror which has to be smaller than the tolerance value to avoid scrapping or reworking. Theestimated form error is usually affected by uncertainty, which depends on both the sample size(number of points measured on the profile/surface) and the sampling strategy (location ofthe points on the profile/surface). The present research work focuses on the second issue andinvestigates the performance of several existing sampling strategies with the ones achievedby two newly presented approaches. These new approaches explore advantages arising byincluding a statistical analysis of a set of machined features in the sampling strategy design.Throughout the paper, a real case study concerning flatness tolerance is used as reference.Keywords: Sampling strategy, geometric tolerance, measuring, CMM, variable selection, PCA.

Unsupervised robust planar segmentation of terrestrial laser scanner point clouds based on fuzzy clustering methods

Terrestrial laser scanning is becoming a common surveying technique to measure quickly and accurately dense point clouds in 3-D. It simplifies measurement tasks on site. However, the massive volume of 3-D point measurements presents a challenge not only because of acquisition time and management of huge volumes of data, but also because of processing limitations on PCs. Raw laser scanner point clouds require a great deal of processing before final products can be derived. Thus, segmentation becomes an essential step whenever grouping of points with common attributes is required, and it is necessary for applications requiring the labelling of point clouds, surface extraction and classification into homogeneous areas. Segmentation algorithms can be classified as surface growing algorithms or clustering algorithms. This paper presents an unsupervised robust clustering approach based on fuzzy methods. Fuzzy parameters are analysed to adapt the unsupervised clustering methods to segmentation of laser scanner data. Both the Fuzzy C-Means (FCM) algorithm and the Possibilistic C-Means (PCM) mode-seeking algorithm are reviewed and used in combination with a similarity-driven cluster merging method. They constitute the kernel of the unsupervised fuzzy clustering method presented herein. It is applied to three point clouds acquired with different terrestrial laser scanners and scenarios: the first is an artificial (synthetic) data set that simulates a structure with different planar blocks; the second a composition of three metric ceramic gauge blocks (Grade 0, flatness tolerance ± 0.1 μm) recorded with a Konica Minolta Vivid 9i optical triangulation digitizer; the last is an outdoor data set that comes up to a modern architectural building collected from the centre of an open square. The amplitude-modulated-continuous-wave (AMCW) terrestrial laser scanner system, the Faro 880, was used for the acquisition of the latter data set. Experimental analyses of the results from the proposed unsupervised planar segmentation process are shown to be promising.

Experimental Study on New Bonding Materials for Developing Nano-Grinding Plates

This paper describes a method for experimental development of a novel fixed abrasive nano-grinding plate (FAG-plate) which is proposed for lapping some rigid brittle materials, such as quartz crystal and silicon. The FAG plate is developed with ultraviolet-cured resin by rapid prototyping technology. The analysis shows that such FAG-plate can keep its grinding ability constant and continuous and it can make the roughness of machined surface reach to nanometer level. Based on experimental comparisons with conventional free abrasive slurry lapping plates, the lapping process using FAG-plate has several distinct advantages. One is that the machining efficiency is significantly improved. The second is that it improves the surface roughness of machined work-pieces, although it decreases the flatness tolerance of materials. Furthermore, the fixed abrasive nano-grinding plate is made by the new bonding materials- ultraviolet curing resin and thus the fabrication of FAG-plate is convenient and economical.

Optimisation of work roll shifting and bending to roll thinner gauge HR coils using genetic algorithm

Rolling of thin gauge hot rolled (HR) coils demands stringent flatness tolerance. Thin HR coils (≤3 mm) are rolled towards the end of any rolling campaign. The profile and flatness of the strip depend on the profile of the loaded roll gap in the mill stands. There are five key factors that influence the loaded roll gap: initial roll surface profile, roll thermal expansion, wear of roll, deflection of roll stack and shifting of work rolls. This paper deals with all these factors individually for the formulation of an objective function in order to minimise the flatness error. The shifting and bending of rolls are the controllable parameters that require optimising. This has been accomplished using a genetic algorithm (GA) optimisation technique.

Support Vector Regression for Determination of Minimum Zone

Probe-type Coordinate Measuring Machines (CMMs) rely on the measurement of several discrete points to capture the geometry of part features. The sampled points are then fit to verify a specified geometry. The most widely used fitting method, the least squares fit (LSQ), occasionally overestimates the tolerance zone. This could lead to the economical disadvantage of rejecting some good parts and the statistical disadvantage of normal (Gaussian) distribution assumption. Support vector machines (SVMs) represent a relatively new revolutionary approach for determining the approximating function in regression problems. Its upside is that the normal distribution assumption is not required. In this research, support vector regression (SVR), a new data fitting procedure, is introduced as an accurate method for finding the minimum zone straightness and flatness tolerances. Numerical tests are conducted with previously published data and the results are found to be comparable to the published results, illustrating its potential for application in precision data analysis such as used in minimum zone estimation.

Linear motion carriage with aerostatic bearings preloaded by inclined iron core linear electric motor

A fundamentally precise and simple linear motion axis design is discussed where the attractive force from the linear motor is used to preload a carriage supported by six rigidly attached porous carbon air bearings. The air bearings are assembled by vacuuming the pads to two orthogonal planes, positioning the carriage above the pads, and then injecting epoxy between the bearings and the carriage. Control of flatness tolerances of the bearings and planes permits over-constraint of the carriage by the bearings, which leads to a high degree of accuracy and moment load capacity via elastic averaging. Good dynamic stiffness is also obtained because of large bearing area and squeezed-film damping. The two orthogonal planes represent an accurate and cost effective geometry that can be created to guide linear motion; and by placing the open-face iron-core motor at the desired position and angle with respect to the bearings, preload forces with equal or otherwise desired relative magnitudes are obtained. Because the attractive force is typically 3–5 times the axial force generated by the motor, the system is inherently stable even in the presence of large externally applied moments that might otherwise induce excessive pitch, yaw, or roll errors.

Flatness tolerance evaluation: an approximate minimum zone solution

This paper is concerned with the problem of flatness tolerance evaluation. First, we introduce the concepts of width and inner radius of point sets, and establish the equivalence between the width of a point set and the inner radius of the convex hull of the self-difference of the set. On this basis, we present an algorithm for calculating the exact minimum zone tolerance of flatness. Second, we prove that an approximation of the inner radius of a convex set can be obtained from the inner radius of the set in fixed direction. On this basis, we present an algorithm for calculating the ‘almost exact’ minimum zone solution. This algorithm is implemented by solving a single linear programming problem, of which the computational complexity is O( n). Numerical examples are given to validate the proposed algorithms.

From support vector machine learning to the determination of the minimum enclosing zone

The verification of form tolerances requires the determination of the minimum enclosing zone according to the ANSI Y14.5M National Standard on Dimensioning and Tolerancing. However, to date many coordinate measuring machines (CMMs) still employ the least-squares method, which has the economic disadvantage of sometimes rejecting good parts. Support vector machines represent a new approach in the area of machine learning, which has been implemented successfully in pattern recognition and regression estimation problems. This article outlines, how the support vector algorithm, as used in classification problems, can be modified in order to identify the minimum enclosing zone for straightness and flatness tolerances. A gradient ascent approach is proposed to identify the solution of the resulting non-convex optimization problem. Numerical results for evaluating the minimum enclosing zone suggest rather promising properties of the employed gradient ascent method.

Finite element analysis of residual-stress-induced flatness deviation in banded carbon seals

Carbon face seals, used in the aircraft engines manufactured by AlliedSignal Engines, are assembled via a shrink-fit procedure which generates residual stresses in both components, resulting in 30–50% of the seals not meeting the required flatness tolerance of three helium light bands (3 HeLB, equal to 0.762 μm ). A two-dimensional, axisymmetric finite element analysis is carried out here to provide a means for better understanding the geometric and processing parameters of the face seals in order to improve their flatness. Results indicate that to obtain a lower value of f d, the flatness deviation, the seal should have a larger inner radius ( R i), a smaller initial radial interference ( δ), a larger thickness of the steel ring ( t s), a smaller thickness of the carbon ring ( t c), and a smaller height ( h t). Also, it is preferable to have a slower cooling rate during the assembly process. It is observed that the coefficient of friction at the interface, μ, does not have any effect on f d. Finally, the process of an “expansion” fit does not contribute towards a reduction in f d, and hence is not worth the effort and cost.

A CAD integrated analysis of flatness in a form tolerance zone

Form tolerance plays an important role in representing features on a solid model. Reported research works on tolerance indicate that the current focus is on modeling form variations directly without defining the form tolerance zones. This paper presents a mathematical definition of the flatness tolerance zone using various parameters to describe its characteristics. By calculating the limits of these parameters, the size, location and orientation of the tolerance zone can be determined. Combining the flatness and size tolerance zones, a final zone can be obtained. This zone represents the actual region of space within which the toleranced surface must lie in order to satisfy both the size and form tolerances. The developed mathematical model is implemented in a 3-D modeling environment so that the user can specify tolerance types and values, and model the tolerance zones. This can be used in verifying the interference between parts during assembly modeling.

Is beta cell dysfunction responsible for flat glucose tolerance curve in primary hypothyroidism? (A hypothesis)

An intimate relationship between thyroid hormones and carbohydrate metabolism has long been recognised and oral glucose load produces flat glucose tolerance curve in patients with primary hypothyroidism. Although delayed glucose absorption was proposed to explain flat glucose tolerance curve exact mechanism remains to be elucidated. Hence this study was undertaken to assess glucose and insulin response to OGTT and IVGTT in 25 freshly detected cases of hypothyroidism and 25 healthy control. The cases were matched for sex, age, BMI, and waist hip ratio with controls. Cases and controls with past or family history of obesity, diabetes mellitus, or hypertension were excluded from study. The biochemical profile of the cases and controls was also comparable except for haemoglobin 111.2±0.31 vs 12.9±0.22 gm/dl)(p=0.0004). Serum cholesterol and triglyceride levels were higher in the cases but difference was not statistically significant Fasting plasma glucose level was significantly lower in hypothyroid patients (78±2.2 vs88±4.4 mg/dl, p=0.049). The oral glucose tolerance curve was fiat with plasma glucose levels significantly lower at 30 minutes. The insulin levels during OGTT were found to be higher in the cases at all stages. There was loss of first phase insulin response to the glucose load during the IVGTT, which was blunted at all stages and the difference was statistically significant at 0 and 3 minutes. Loss of first phase insulin response to IV glucose suggests that there is evidence of beta-cell dysfunction. Patients with hypothyroidism were more insulin sensitive than control and insulin secretion was comparable with controls. Therefore fiat glucose tolerance curve can be explained by absence of insulin priming effect leading to decreased glucose absorption followed by increased glucose disposal because of higher insulin levels following OGTT and increased glucose disposal caused by increased insulin sensitivity.

Manufacturability Analysis of Flatness Tolerances in Solid Freeform Fabrication

Increasingly, Solid Freeform Fabrication (SFF) processes are being considered for creating functional parts. In such applications, SFF can either be used for creating tooling (i.e., patterns for casting, low volume molds, etc.) or directly creating the functional part itself. In order to create defect free functional parts, it is extremely important to fabricate the parts within allowable dimensional and geometric tolerances. This paper describes a systematic approach to analyzing manufacturability of parts produced using SFF processes with flatness tolerance requirements on the planar faces of the part. Our research is expected to help SFF designers and process providers in the following ways. By evaluating design tolerances against a given process capability, it will help designers in eliminating manufacturing problems and selecting the right SFF process for the given design. It will help process providers in selecting a build direction that can meet all design tolerance requirements.

A new convex-hull based approach to evaluating flatness tolerance

In this paper, we consider a minimum-zone evaluation problem for flatness to determine the minimum tolerance zone enclosing all the measurement points obtained from a surface. For the problem, a new geometric approach called the ‘convex-hull edge method’ (CONHEM) is proposed. The method guarantees the minimum zone tolerance for a given set of measurement points. Several examples discussed by other researchers are illustrated to compare the method with some existing approaches.

Part Form Errors Predicted from Machine Tool Performance Measurements

Machine tool performance testing, as defined by ISO 230 and ANSI B5.54, has been successfully used to maintain and improve the accuracy and repeatability of production-level machine tools. In this study, a controlled series of experiments have been used to test the efficacy of these performance tests in the prediction of part form errors. Results are shown for flatness, squareness, position, and profile tolerances. The experimental results suggest that standard machine tool performance tests can also be used to predict the “best-case” tolerances that can be achieved for particular part features.

Straightness and flatness tolerance evaluation: an optimization approach

This paper presents an optimization approach that could be used to calculate exact values of straightness and flatness errors as defined by the ANSI Y14.5M standards on geometric dimensioning and tolerancing. The straightness and flatness error evaluation problems are formulated as nonlinear optimization problems with linear objective function and nonlinear constraints. Because of the special structure of the problem, a linear search method is developed that reduces the nonlinear problem to a linear programming problem with only two constraints. Examples are presented to compare the optimization approach with the least-squares method and some exact methods. The results show that the optimization procedures presented in this paper provide exact values of straightness and flatness errors and are superior to the existing methods in terms of computation time.