George Moraru

Repairing triangle meshes built from scanned point cloud

The Reverse Engineering process consists of a succession of operations that aim at creating a digital representation of a physical model. The reconstructed geometric model is often a triangle mesh built from a point cloud acquired with a scanner. Depending on both the object complexity and the scanning process, some areas of the object outer surface may never be accessible, thus inducing some deficiencies in the point cloud and, as a consequence, some holes in the resulting mesh. This is simply not acceptable in an integrated design process where the geometric models are often shared between the various applications (e.g. design, simulation, manufacturing). In this paper, we propose a complete toolbox to fill in these undesirable holes. The hole contour is first cleaned to remove badly-shaped triangles that are due to the scanner noise. A topological grid is then inserted and deformed to satisfy blending conditions with the surrounding mesh. In our approach, the shape of the inserted mesh results from the minimization of a quadratic function based on a linear mechanical model that is used to approximate the curvature variation between the inner and surrounding meshes. Additional geometric constraints can also be specified to further shape the inserted mesh. The proposed approach is illustrated with some examples coming from our prototype software.

On a Robust Modeling of Piezo-Systems

This paper proposes a new modeling approach which is experimentally validated on piezo-electric systems in order to provide a robust Black-box model for complex systems control. Industrial applications such as vibration control in machining and active suspension in transportation should be concerned by the results presented here. Generally one uses physical based approaches. These are interesting as long as the user cares about the nature of the system. However, sometimes complex phenomena occur in the system while there is not sufficient expertise to explain them. Therefore, we adopt identification methods to achieve the modeling task. Since the microdisplacements of the piezo-system sometimes generate corrupted data named observation outliers leading to large estimation errors, we propose a parameterized robust estimation criterion based on a mixed L2 – L1 norm with an extended range of a scaling factor to tackle efficiently these outliers. This choice is motivated by the high sensitivity of least-squares methods to the large estimation errors. Therefore, the role of the L1-norm is to make the L2-estimator more robust. Experimental results are presented and discussed. [DOI: 10.1115/1.4005499]

Feature selection for complex systems monitoring: An application using data fusion

Emergence of automated and flexible production means leads to the need of robust monitoring systems. Such systems are aimed at the estimation of the production process state by deriving it as a function of critical variables, called features, that characterize the process condition. The problem of feature selection, which consists, given an original set of features, in finding a subset such the estimation accuracy of the monitoring system is the highest possible, is therefore of major importance for sensor-based monitoring applications. Considering real-world applications, feature selection can be tricky due to imperfection on available data collections: depending on the data acquisition conditions and the monitored process operating conditions, they can be heterogeneous, incomplete, imprecise, contradictory, or erroneous. Classical feature selection techniques lack of solutions to deal with uncertain data coming from different collections. Data fusion provides solutions to process these data collections altogether in order to achieve coherent feature selection, even in difficult cases involving imperfect data. In this work, condition monitoring of the tool in industrial drilling systems will serve as a basis to demonstrate how data fusion techniques can be used to perform feature selection in such difficult cases.

A design-for-casting integrated approach based on rapid simulation and modulus criterion

This paper presents a new approach to the design of cast components and their associated tools. The current methodology is analysed through a case study and its main disadvantages underlined. Then, in order to overcome these identified drawbacks, a new approach is proposed. Knowing that this approach is mainly based on a rapid simulation of the process, basics of a simplified physical model of solidification are presented as well as an associated modulus criterion. Finally, technical matters for a software prototype regarding the implementation of this Rapid Simulation Approach (RSA) in a CAD environment are detailed.

Active control of a vibrating beam in milling

The vibrations while Milling often impact the results, sometimes generating very important cost because of the lack of quality for high value parts as well as cutting tool wear due to chatter phenomenon that happens during unstable vibrations. To mitigate this phenomenon, many techniques exist like passive and semi-active methods but the active control in milling, which is not as widespread in turning or boring, remains one of the most promising ways. This article will deal briefly with these techniques before explaining our two system models: cutting process and the vibrating beam, considered as an accurate enough model of a long slender rotary tool, which will be after coupled. Then, we will study the active control of the obtained system following three control strategies: the H∞ compensator, LQG one and μ synthesis compensator.

Generic Models of Piezo-Actuators and Experimental Validation for Smart Applications

In previous papers, we suggested piezo-actuators models and compared them to existing works with respect to sinusoidal solicitations. The current paper aims to experimentally validate and refine them. For this purpose, the piezo-device is integrated in a well known system. This reveals that the modeling of the whole system requires additional artefact and good choice of simulation methods. Then we study the whole system dynamics in order to check the validity of our models. Thereafter, the final model is reversed in order to elaborate control loops in smart applications.Copyright

User-Oriented Simulation Models of Piezo-Bar Actuators: Part I—Linear Approach

The emergence of electro-active materials such as piezoelectric ones allows recently to think back actuating and sensing functions thanks to new principles of electromechanically conversion of energy. The interesting properties of these materials lead up to considering the generalization of their use in various applications such as automobile, aeronautics or machining. However this enthusiasm quickly goes away when a common engineer has to be confronted to the quasi absence of ready-to-be-used models of devices made of these materials [14]. This comes from the fact that piezoelectricity still remains the mind of the experts of materials. This is why in this paper we aim to formalize and wittingly simplify existing approaches of modeling piezo-actuators. Our goal is to make available to all a method of constituting at least a basic library of piezo-actuators models. This set of models is intended and designed to be completed by more deepen models integrating several aspects neglected in basic models.© 2009 ASME

User-Oriented Simulation Models of Piezo-Bar Actuators: Part II—Integration of Nonlinearities

In [1] we proposed an approach of formalizing piezo-bar actuator dynamics models in the engineer languages. The proposed models were based on a first approximation considering that the piezo-material is linear. However, as soon as the solicitations increase one will realize that this assumption is no longer valid because non-linearities are observed. And these phenomena can seriously affect the device performances. That is why several works are conducted in order to well understand the phenomena and eventually propose means of controlling them. So, above of all we shall give in this paper an overview of existing approaches. As said in [2], all these non-linearities in piezoelectric materials are well analyzed but mostly in the framework of the fundamental physics of crystals and thermodynamics and these descriptions are extremely difficult to handle. Therefore is important to make a bridge between the fundamental studies of piezoelectric materials and classical engineering field. It is actually the purpose of this paper. We will see that due to the complexity of the phenomena and especially numerical and algebraic troubles, some simplifications could be necessary.Copyright