MODELISATION CINEMATIQUE DES MOBILITES DE COMPOSANTS POUR DES OPERATIONS D’ASSEMBLAGE ET DE DESASSEMBLAGE
Author: Iacob, Robert-Eugen
Supervisor: Léon, J. & Mitrouchev, P.
Institution: Universite de Grenoble
Assembly/Disassembly (A/D) simulations are important to improve design and efficiency of product development processes. In order to get efficient simulation processes it is important to simulate all the possible relative movements between the components in a mechanical assembly. This is important both in the context of interactive simulation and in the context of immersive/real time simulations. If some categories of movements are missing, simulations can loose key configurations, hence they may be no longer meaningful.
The scope in research, whiting this thesis deals, in the first time, with a theoretical approach for developing of a kinematical model able to represent all the valid relative movements of a reference component with respect to its surrounding ones, which form a family of trajectories. It is based on the analysis of the three basic movements: translation, rotation and helical ones. In order to determine the compatibility between different families of trajectories, a bi-quaternion is associated to each contact area between the different components. All possible trajectories for each component are analyzed, for the three basic type of movements, in order to find the compatible ones, which leads to the specification of an operator. Thus, the results of all the possible associations are determined and a general combination operator is proposed. The properties of this later are demonstrated as well. The operator can form, in a real time simulation environment, the basis for determining at each moment, the valid movements between components, thus reducing the complexity of collision detection algorithms. The A/D simulations can be performed either from an automated or interactive point of view using standard computer equipment or through immersive and real-time simulation schemes. In order to address this diversity of configurations, a simulation framework is (was) developed. It is based on a new simulation preparation process which allows a simulation process to address up to two types of shape representations, i.e. B-Rep NURBS and polyhedral ones, at the same time, thus handling efficiently the configurations where 3D shape representations of assemblies play a key role. In order to illustrate the simulation process the automatic identification of contacts in a 3D product model and their corresponding list is described. After the identification stage, an interpretation of the results is needed in order to have the complete list with the mechanical contacts for a product. The preparation process is performed within three major stages: model tessellation, surface merging and contacts identification. The framework is based on STEP exchange format. This software environment can assist designers to achieve a satisfactory assembly analysis rapidly and can reduce the lead-time of product development. Further consequences of the present work is its ability to produce models and treatments that improve integration of assembly models in immersive environments taking into account of the haptic and visual models needed. Assembly/Disassembly simulations using haptic devices are facing difficulties while simulating insertion/extraction operations such as removing cylinders from holes for example. In order to address this configuration as well as others, an approach based on the kinematic model and on the simulation framework is proposed.