Laboratoire Universitaire de Recherche en Production Automatisée

Additive manufacturing (AM) is emerging as an important manufacturing process and a key technology for enabling innovative product development. Design for additive manufacturing (DFAM) is nowadays a major challenge to exploit properly the potential of AM in product innovation and product manufacturing. However, in recent years, several DFAM methods have been developed with various design purposes. In this paper, we first present a state-of-the-art overview of the existing DFAM methods, then we introduce a classification of DFAM methods based on intermediate representations (IRs) and product's systemic level, and we make a comparison focused on the prospects for product innovation. Furthermore, we present an assembly based DFAM method using AM knowledge during the idea generation process in order to develop innovative architectures. A case study demonstrates the relevance of such approach. The main contribution of this paper is an early DFAM method consisting of four stages as follows: choice and development of (1) concepts, (2) working principles, (3) working structures, and (4) synthesis and conversion of the data in design features. This method will help designers to improve their design features, by taking into account the constraints of AM in the early stages.

This paper focuses on a sub-class of Dynamic Fault Trees (DFTs), called Priority Dynamic Fault Trees (PDFTs), containing only static gates, and Priority Dynamic Gates (Priority-AND, and Functional Dependency) for which a priority relation among the input nodes completely determines the output behavior. We define events as temporal variables, and we show that, by adding to the usual Boolean operators new temporal operators denoted BEFORE and SIMULTANEOUS, it is possible to derive the structure function of the Top Event with any cascade of Priority Dynamic Gates, and repetition of basic events. A set of theorems are provided to express the structure function in a sum-of-product canonical form, where each product represents a set of cut sequences for the system. We finally show through some examples that the canonical form can be exploited to determine directly and algebraically the failure probability of the Top Event of the PDFT without resorting to the corresponding Markov model. The advantage of the approach is that it provides a complete qualitative description of the system, and that any failure distribution can be accommodated.

Nowadays, the management of product geometrical variations during the whole product development process is an important issue for companies’ competitiveness. During the design phase, geometric functional requirements and tolerances are derived from the design intent. Furthermore, the manufacturing and measurement stages are two main geometric variations generators according to the two well-known axioms of manufacturing imprecision and measurement uncertainty. GeoSpelling as the basis of the geometrical product specification standard enables a comprehensive modeling framework and an unambiguous language to describe geometric variations covering the overall product lifecycle thanks to a set of concepts and operations based on the fundamental concept of the “Skin Model.” In contrast, only few research studies have focused on the skin model representation and simulation. The skin model as a discrete shape model is the main focus of this work. We investigate here discrete shape and variability modeling fundamentals, Markov Chain Monte Carlo simulation techniques and statistical shape analysis methods to represent, simulate, and analyze skin models. By means of a case study based on a cross-shaped sheet metal part, the results of the skin model simulations are shown here, and the performances of the simulations are described.

Additive Manufacturing (AM) technologies have gained extensive applications due to their capability to manufacture parts with complex shape, architected materials and multiple structure. However, the dimensional and geometrical accuracy of the resulting product remain a bottleneck for AM regarding quality assurance and control. Design for Additive Manufacturing (DfAM) aims at using different methodologies to help designer take into account the technological or geometrical specificities of AM, to maximize product performance during the design stage. As a main concern in DfAM, the consistency between the digital product and the final outcome should be effectively assessed. Therefore, the geometric deviations between designed model and real product should be modeled, in order to derive correction and compensation plans to increase geometrical accuracy, or to predict product performance more precisely. In this paper, a new deviation modeling method based on the STL file is proposed. A new shape transformation method is developed based on contour point displacement. In each slice, systematic deviations are represented by polar and radial functions and random deviations are modeled by translating the contour points with a given distance derived from the random field theory. The proposed method makes a good prediction of both repeatable and unexpected deviations of product shape, thus providing the designer with meaningful information for design improvement.

This paper deals with the identification of discrete-event manufacturing systems that are automated using a programmable logic controller (PLC). The behavior of the closed-loop system (PLC and Plant) is observed during its operation and is represented by a single long sequence of observed input/output (I/O) signals vectors. The proposed method follows a black-box and passive identification approach that allows addressing large and complex industrial DES and yields compact and expressive interpreted Petri net (IPN) models. It consists of two complementary stages; the first one obtains, from the I/O sequence, the reactive part of the model composed by observable places and transitions. The I/O sequence is also mapped into a sequence of the created transitions, from which the second stage builds the non observable part of the model including places that ensure the reproduction of the observed input output sequence. This method, based on polynomial-time algorithms on the size of the input data, has been implemented as a software tool that generates and draws the IPN model; it has been tested with input/output sequences obtained from real systems in operation. The tool is described and its application is illustrated through a case study.

Geometric part deviations, which are inevitably observed on every manufactured workpiece, have distinct effects on the assemblability as well as on the function and quality of physical artefacts. As a consequence, geometric variations management is an important issue for manufacturing companies. However, assessing the effects of form deviations already in virtual product realization remains an important challenge. This paper illustrates and summarizes the current status and development trends of the Skin Model Shape paradigm, which provides an operationalization and a digital representation of the Skin Model concept for modelling product shape variability and hence may serve as a comprehensive model for computer-aided variations management.

The modeling of plant behavior is often essential in the design, performance analysis or diagnosis of discrete event systems (DES). Yet this task remains a difficult one for which little research has been devoted. In this paper, we propose a technique for building behavioral models specific to large-scale plants, in order to perform a formal verification of the controller by means of "model-checking". In this aim, we have opted to use a modular approach with an appropriate class of automata. To obtain the overall plant model, parallel evolutions of the elementary automata are to be coordinated by a sequencer that ensures consistency of these evolutions

In the context of the reliability of critical systems, we focus on Dynamic Fault Tree (DFT) analysis. Our contribution is the definition of an algebraic framework allowing to determine the structure function of DFTs and to extend the analytical methods commonly used to analyze Static Fault Trees to DFTs. First, we review the main approaches which allow to analyze DFTs, as well as their limits. Then, the algebraic framework allowing the modelling of DFTs is presented. This algebraic framework is based on a temporal model of events, and on the definition of three temporal operators allowing to model the sequences of appearance of events. These temporal operators allow to algebraically define the behaviour of dynamic gates, and hence the structure function of DFTs. A probabilistic model of these dynamic gates is given to determine the failure probability of the top event of DFTs from this structure function. Finally, we show how the structure function of DFTs can be simplified to a canonical form thanks to some theorems and to a minimal form thanks to the definition of a minimization criterion. Last, we show how DFTs can be analyzed analytically and directly from this minimal canonical form of the structure function. We illustrate this approach on two DFT examples from the literature.

ABSTRACT. Programmable Logic Controllers ensure the control of many reactive systems. These controllers are most of the time programmed with the languages defined in the IEC 61131– 3 standard. Our goal is the verification of safety properties of programs written in one of these languages: the Ladder Diagram. The main approaches in this field are based on Model-Checking. We propose in this article a Theorem-Proving method by defining a formal framework to express and handle the Ladder Diagram programs with a specific algebra. Firstly, we translate the specific statements of the language into this algebra and we give some general theorems. Then, we present on an example an analysis leading to the verification of safety properties. RÉSUMÉ. Les automates programmables industriels assurent le contrôle-commande d’un grand nombre de systèmes réactifs. Leur programmation se fait le plus souvent avec des langages définis dans la norme IEC 61131–3. Notre objectif est la vérification de propriétés de sûreté dans les programmes écrits dans l’un de ces langages: le “Ladder Diagram”. Les principales approches dans le domaine abordent le problème par “Model-Checking”. Pour notre part, nous nous proposons d’explorer la voie du “Theorem-Proving ” en définissant un cadre formel pour exprimer et manipuler les programmes “Ladder Diagram ” dans une algèbre adaptée. Après avoir traduit les primitives de ce langage dans cette algèbre et donné des théorèmes généraux, nous présentons sur un exemple une analyse conduisant à la vérification de propriétés de sûreté.

This correspondence paper deals with the sensor placement optimization problem in the context of indoor multiple inhabitants location tracking to solve ambient assisted living problems. Binary sensors, like passive infrared (PIR) sensors, are used to guaranty specific coverage requirements and allow privacy respecting. Moreover, within real home environments, different kinds of obstacles (like walls, high furniture, etc.) can affect the detection capacity of PIR sensors. This paper proposes an integrated framework devoted to optimize the placement of sensors and PIR sensors in smart homes by taking into account physical topologies and coverage precision constraints. An integer linear programming problem is formalized and a case study illustrates the applicability of the proposed approach and the scalability of the optimization method.

A method to perform tridimensional analysis and tridimensional synthesis of machining tolerances is presented. The model relies on the small displacement torsor concept and on the computer aided tolerancing approach. The link between process planning and functional tolerances with torsor chains according to workpiece set-ups is exposed. An example shows how the model is used to determine automatically geometrical variations of the workpiece knowing geometrical variations of each part (part-holder, positioning devices, machined surfaces, etc.).

International audience

This paper addresses the problem of discovering a Petri Net (PN) from a long event sequence representing the behavior of discrete-event processes. A method for building a 1-bounded PN able to execute the events sequence S is presented; it is based on determining causality and concurrence relations between events and computing the t-invariants. This novel method determines the structure and the initial marking of an ordinary PN, which reproduces the behavior in S. The algorithms derived from the method are efficient and have been implemented and tested on numerous examples of diverse complexity.

The quality of the interfaces between parts ensures the assembly requirements of a mechanism and the right positioning of functional surfaces. When defining a mechanism, a designer analyzes the failures generated by the geometrical defects of the junction surfaces between the parts. To formalize the design intents clearly, the method proposed, named TLIC, uses positioning tables of the parts to clearly indicate the set up surfaces associated as features and the preponderance order of the features. The requirements of assembly between parts and the tolerancing of the interfaces can then be generated automatically by defining the reference systems.

Robust product designs are characterized by their insensitivity to disturbances and noise, such as geometric part deviations, which are inevitably observed on every manufactured workpiece. These observed deviations are covered by the axioms of manufacturing imprecision and measurement uncertainty, which convey the concepts of variability and uncertainty as fundamental aspects of robust design. In order to ensure the product function though the presence of these geometric part deviations without building physical artefacts, tolerance simulations are employed in the context of computer-aided tolerancing. Motivated by the shortcomings of existing tools, the concept of Skin Model Shapes has been developed as a novel paradigm for the computer-aided tolerance analysis. This paper presents a comparative study on the standard procedure for the tolerance analysis employing proprietary CAT tools and the tolerance simulation based on Skin Model Shapes, where a focus is set on the methodology and result interpretation. For this purpose, exemplary study cases are highlighted. Based on the comparisons, recommendations for the use of CAT tools in the context of tolerance analysis and robust design are derived.

In 5-axis high-speed milling, large incoherent movements of rotary axes around the singular point are known to be a problem. Correction methods found in the literature deal mostly with the collision that may happen between the tool and the part but not with the feedrate slowdowns which affect surface quality and machining productivity. The method proposed in this paper addresses both geometrical and productivity issues by modifying the tool axes orientation while respecting maximum velocity, acceleration and jerk of the machine tool axes. The aim is to detect these behaviours and replace the considered portion of the tool path by a patch curve respecting kinematical constraints of the machine tool. Compared to previous works, the inserted patch curve is not constrained to pass through the singularity but respect tangential constraints to ensure the monotony of the tool path and is also connected with the rest of the tool path to ensure a continuity up to the third derivative in order to fulfil jerk limitations. For that purpose, the initial articular positions of the rotary axes around the singular point are fitted with B-spline curves, modified and finally discretised for linear interpolation. Experimental investigations on a test part are carried out to show the efficiency of the method in terms of feedrate and surface quality.

The integration of more physical properties into the Skin model is fundamental for extending the tolerancing process to the different phases of the product lifecycle. This paper presents a study of the deformation effects on the Skin model provoked by the thermal and working environment of the workpiece. The proposed methodology departs from the Skin model at room temperature, and generates Skin Model Shapes by performing a Finite Element Analysis (FEA). The simulation tool has been successfully tested in the study of a practical industrial application, a gas turbine blade, which combines many of the nowadays challenges of CAD, FEA and CAT.

Computer-Aided Design and Applications is an international journal on the applications of CAD and CAM. It publishes papers in the general domain of CAD plus in emerging fields like bio-CAD, nano-CAD, soft-CAD, garment-CAD, PLM, PDM, CAD data mining, CAD and the internet, CAD education, genetic algorithms and CAD engines. The journal is aimed at all developers and users of CAD technology to ptovide CAD solutions for various stages of design and manufacturing. The journal publishes all about Computer-Aided Design and Computer-Aided technologies.

This article deals with the problem of discovering a Petri net (PN) model of a discrete-event system, starting from the observation of long-event sequences. Precisely, given an interpreted PN (IPN) system modeling the relations between input and output events of the system (i.e., the reactive/observable behavior), the internal state evolutions of the system (i.e., the unobservable behavior) are first discovered and then modeled. The proposed unobservable discovery takes advantage of the novel concept of interpreted sequences, which better characterize the system and model the behavior by considering both observable markings (outputs) and transition firings (inputs). The unobservable modeling is approached as a net synthesis problem. It relies on an optimization-based procedure that identifies the complementary structure; in particular, places only are added to the original model. Note to Practitioners-Black-box identification procedures process an input-output sequence recorded for a long period of time during the functioning of a closed-loop controlled system, and then return a model of the system. However, even if these models simulate well the recorded sequence, they are not very accurate. Indeed, they simulate also other sequences that, in general, are not admitted by the real system. The method proposed here aims to make more accurate these models by discovering the unobservable behavior of a controlled system, related to evolutions of the internal state (and variables) of the system without changing the capability of simulating the observed behavior.

Control system programs are usually validated by testing prior to their deployment. Unfortunately, testing is not exhaustive and therefore it is possible that a program which passed all the required tests still contains errors. In this paper we apply techniques of automatic verification to a control program written in ladder logic. A model is constructed mechanically from the ladder logic program and subjected to automatic verification against requirements that include timing. This consists of an exhaustive search of the model of the program, thus eliminating the drawback of testing. We believe that automatic verification can substantially enhance current validation procedures for control programs.