Hugues Favreliere

Modeling of 2D and 3D assemblies taking into account form errors of plane surfaces.

The tolerancing process links the virtual and the real worlds. From the former, tolerances define a variational geometrical language (geometric parameters). From the latter, there are values limiting those parameters. The beginning of a tolerancing process is in this duality. As high precision assemblies cannot be analyzed with the assumption that form errors are negligible, we propose to apply this process to assemblies with form errors through a new way of allowing to parameterize forms and solve their assemblies. The assembly process is calculated through a method of allowing to solve the 3D assemblies of pairs of surfaces having form errors using a static equilibrium. We have built a geometrical model based on the modal shapes of the ideal surface. We compute for the completely deterministic contact points between this pair of shapes according to a given assembly process. The solution gives an accurate evaluation of the assembly performance. Then we compare the results with or without taking into account the form errors. When we analyze a batch of assemblies, the problem is to compute for the nonconformity rate of a pilot production according to the functional requirements. We input probable errors of surfaces (position, orientation, and form) in our calculus and we evaluate the quality of the results compared with the functional requirements. The pilot production then can or cannot be validated.

Multi scale modal decomposition of primary form, waviness and roughness of surfaces

This article introduces an innovative method for the multi-scale analysis of high value-added surfaces, which consists of applying a method based on a new parameterization. This kind of surface parameterization refers to natural modes of vibration, and is therefore named modal parameterization. It allows us to characterize the form, waviness and roughness defects of a surface. This parameterization opens up new fields of analysis, such as the appearance quality of surfaces. It is thereby possible to decompose a measured surface in a vector basis, of which vectors are represented by plane natural eigenmodes sorted by frequency and complexity. Different filtering operations can then be produced, such as extracting the primary form of the surface. To analyze the perceived quality of surfaces, these investigations focus on two approaches: that appearance defects have small periodicity, and that there is a link between curvatures and the visual impact of an anomaly. This methodology is applied to two prestige lighters, whose surfaces were measured by extended field confocal microscopy. Moreover, a prospect of this work is to develop an augmented-reality-type monitoring tool for sensory experts.

Development of low frequency, insulating thick diaphragms for power MEMS applications

Major challenges of micro thermal machines are the thermal insulation and mechanical tolerance in the case of sliding piston. Replacing piston by membrane in microengines can alleviate the latter and lead to planar architectures. However, the thermal isolation would call for very thick structures which are associated to too high resonant frequencies which are detrimental to the engine performances. A thermal and mechanical compromise is to be made. On the contrary, based on fluid structure interaction, using an incompressible fluid contained in a cavity sealed by deformable diaphragm it would be possible to design a thick, low frequency insulating diaphragm. The design involves a simple planar geometry that is easy to manufacture with standard microelectronics methods. An analytical fluid-structure model is proposed and theoretically validated. Experimental structures are realized and tested. The model is in agreement with the experimental results. A dimensionless model is proposed to design hybrid fluid structures for micromachines.

Multi-scalar analysis of hip implant components using modal decomposition

This paper presents a metrological analysis of hip prosthesis components. When changing ceramic prostheses, the surgeon sometimes finds traces of alloy lying in the insert or the femoral head. These traces can be thin and accurate or as a wide band. From the measurements made on the contact areas of hip prosthesis components, we analyse these phenomena by highlighting the defects of form, waviness and roughness of these surfaces using a novel geometric parameterization (namely modal parameterization). The aim of this work is to isolate these defects to characterize the prostheses components. We show that this parameterization allows a multi-scale analysis of surfaces regardless of the type of wear of the prosthesis, and that the results offer some relevant explanations to the analysis of visible damage on the prostheses. In a later study, we are going to analyse the defects influence on the alteration of the performance of hip prostheses.

How Form Errors Impact on 2D Precision Assembly with Clearance

Most models of assembling simulations consider that form errors are negligible, but how can this assumption be assessed? When clearances are high, form deviations can be neglected, but on the case of very precise mechanisms with small clearances, this assumption can lead to non-accurate models. This paper is the continuation of our previous works presented at IPAS 2008 dealing with the assembly of two parts regarding their form deviation. The proposed method considers the positioning of the pair of surface with a given external force to identify contact points. The parts relative positioning is expressed by a small displacement torsor that can be transferred to any referee and compared to the functional requirement. The objective of this paper is to identify the clearance domain of a mechanical linkage regarding the form deviation of parts. Several parameters are identified as influent such as the clearance value, the straightness of the form deviation and the localization of the ideal least squared associated shape.

Optimisation of a stamping process by a design of experiment linked to a modal analysis of geometric defects

The aim of this work was to present a method that gives an optimized set of values for the process parameters in order to obtain stamped parts with the fewest defects. The springback, influenced by process parameters, is one of the sources of defects. The process is simulated by the finite element method. A design of experiments is used to compute the mathematical model and to minimize the trials number. The defects are characterized by a set of modal shapes. A defect criterion is calculated from this decomposition. Then an optimisation is made by minimizing of this criterion in order to obtain the best process parameters. An example is shown in order to explain the method.

Extended visual appearance texture features

The research purpose is to improve surface characterization based on what is perceived by human eye and on the 2006 CIE report. This report defines four headings under which possible measures might be made: color, gloss, translucency and texture. It is therefore important to define parameters able to discriminate surfaces, in accordance with the perception of human eye. Our starting point in assessing a surface is the measurement of its reflectance (acquisition of ABRDF for visual rendering), i.e. evaluate a set of images from different angles of lighting rather than a single image. The research question is how calculate, from this enhanced information, some discriminating parameters. We propose to use an image processing approach of texture that reflects spatial variations of pixel for translating changes in color, material and relief. From a set of images from different angles of light, we compute associated Haralick features for constructing new (extended) features, called Bidimensional Haralick Functions (BHF), and exploit them for discriminating surfaces. We propose another framework in three parts such as color, material and relief.

Syntactic texture and perception for a new generic visual anomalies classification

The research purpose is to improve aesthetic anomalies detection and evaluation based on what is perceived by human eye and on the 2006 CIE report.1 It is therefore important to define parameters able to discriminate surfaces, in accordance with the perception of human eye. Our starting point in assessing aesthetic anomalies is geometric description such as defined by ISO standard,2 i.e. traduce anomalies description with perception words about texture divergence impact. However, human controllers observe (detect) the aesthetic anomaly by its visual effect and interpreter for its geometric description. The research question is how define generic parameters for discriminating aesthetic anomalies, from enhanced information of visual texture such as recent surface visual rendering approach. We propose to use an approach from visual texture processing that quantify spatial variations of pixel for translating changes in color, material and relief. From a set of images from different angles of light which gives us access to the surface appearance, we propose an approach from visual effect to geometrical specifications as the current standards have identified the aesthetic anomalies.

Discrete Modal Decomposition for surface appearance modelling and rendering

Controlling surface appearance has become essential in the supplier/customer relationship. In this context, many industries have implemented new methods to improve the sensory inspection, particularly in terms of variability. A trend is to develop both hardware and methods for moving towards the automation of appearance inspection and analysis. If devices inspired from dimensional control solutions generally allow to identify defects far apart the expected quality of products, it do not allow to quantify finely appearance anomalies, and decide on their acceptance. To address this issue, new methods devoted to appearance modelling and rendering have been implemented, such as the Reflectance Transformation Imaging (RTI) technique. By varying the illumination positions, the RTI technique aims at enriching the classical information conveyed by images. Thus each pixel is described by a set of values rather than one value classically; each value corresponding to a specific illumination position. This set of values could be interpolated or approximated by a continuous model (function), associated to the reflectance of the pixel, generally based on a second order polynomial (namely, Polynomial Texture Mapping Technique). This paper presents a new approach to evaluate this information from RTI acquisitions. A modal projection based on dynamics (Discrete Modal Decomposition) is used to estimate surface reflectance on each measurement point. After presenting the acquisition device, an application on an industrial surface is proposed in order to validate the approach, and compare it to the more classical polynomial transformation. Results show that the proposed projection basis not only provides closer assessment of surface reflectance (modelling) but also yields to a more realistic rendering.

Statistical Assemblies with form Errors — A 2D Example

When dealing with precision in tolerancing of assembly systems, the modelling complexity of the mechanism increases. At first, one can distinguish the 1D tolerancing approach that only concerns variations of dimension. Then, several models are defined to set 3D tolerances, considering that the form error is negligible compared to the orientational and translational variations. Finally, some approaches are proposed to take into account the form variations in the tolerancing of mechanisms. However, some modelling approaches considers the form error as a tolerance zone to add to the 3D tolerances as defined by Rule#l of the ASME standard, or ISO 8015. This paper proposes another point of view, considering the positioning of parts through contact points of their rigid deviation shapes under a defined assembly force and set-up. Rather than considering the positioning of a single part, here is proposed an approach of batch parts assembly by a statistical description of shapes. The result of the method is a statistical positioning error of one part on the other considering the form deviations of parts.