Tolerance Analysis by Adaptative Polyhedra – AToPAd

Characterization of the geometric variability throughout the product life cycle.
Simulation of the realistic behavior of mechanism and to develop new theoretical basis for multi-physical tolerance. The theoretical developments and digital tools implemented in the AToPAd project will systematically validate on laboratory examples, on first, and then applied on industrial mechanism proposed by industrial partners. One of the major originality of this project is that the developed tools will be shared in open source format. In addition, a CAD library of studied systems will be freely available. Finally, guidelines will be defined concerning the acuity level to be met and the associated modeling to develop according to the functional requirement and expected behavior of the system.

Further research work in geometric and multi-physics tolerancing was proposed by considering a discrete and realistic representation of shapes (Skin Model Shapes), coupled with tolerance analysis methods based on polyhedron models. Through this innovative coupling, the project contributes to: 1) Characterizing geometric variability throughout the product life cycle. 2) Simulating the realistic behavior of assemblies and developing new foundations for multi-physics tolerancing. Theoretical developments and digital tools implemented in the AToPAd project will be validated on laboratory examples, but also on applications provided by industrial partners. One of the original features of this project is that the tools developed are shared in open source. In addition, a CAD library of the systems used to qualify the tools is made available. Design guides recommending the acuity of a modeling necessary for a mechanical system with respect to a functional requirement and an expected behavior will be implemented. The project contributes as a whole to the development of the digital twin of mechanical assemblies which is a challenge for the digital component of the factory of the future. A first publication was made in June 2022 of an open source tool for generating Skin Model Shapes in the SkinModel component of version 2.0.2 of the PolitoCAT application.

Creation of a users community dedicated to the open source platform of the AToPAd project.
Creation of a open database of examples.

An integrated open source CAT based on Skin Model Shapes by Restrepo at al. presented at the 17th CIRP Conference on Computer Aided Tolerancing.
PolitoCAT v2.0.2 for Windows64, a free software under the GNU LGPL license, with a kernel based on politopix and a graphical interface. This is the first contribution to the AToPAd project.

The development of innovative manufacturing processes leads to design innovative and optimized products with both complex architecture and original geometries. These technological breakthroughs forced the engineers to rethink the way we design and integrate these new functionalities.
The control of the geometric variability of mechanical systems is based on the modeling of tolerances and the main objective is to qualify the conformity of a mechanical system with respect to functional requirements (clearance, flush, alignment, etc.) according to the geometric variations of the parts.
Actually, we are facing to a significant disrupting between the continuous increasing functionalities and capacities of production and metrology equipment, while tolerance simulation tools have serious limitations, mainly due to the complexity of the mathematical tools to be implemented. Closing these critical gaps to obtain realistic simulations of the behavior of the assemblies requires major developments at two different scales:
• At the part level, to integrate representative geometric details of the production processes,
• At the mechanism level, to integrate a contact architecture coupled with a behavior representative of the functioning of a mechanical system.

At the part scale, the integration of shape defects drastically increases the complexity of contact modeling. This leads tolerance analysis tools to make assumptions that limit the type of part variations while specializing the types of architecture (isostatic or hyperstatic), integrating (or not) the mobility of the mechanism, addressing (or not) local deformations of contact surfaces and part stiffness.
Due to the complexity of the physical phenomena to address, it is necessary to rethink and develop an adaptive acuity of the system modeling in relation to the functional requirements to be met.
The AToPAd project aims to overcome these scientific bottlenecks, in particular by developing realistic tools for characterizing shape defects at the part scale. The integration of these defects must be combined with the deformation of the contact surfaces. Simulation of these defects and deformations at the mechanism scale will ensure continuity between these different scales and validate their overall performance.

To this end, a further study of research works in geometric for a multi-physical tolerancing approach is proposed, considering a discrete and realistic representation of shapes (Skin Model Shapes) developed by LURPA coupled with tolerance analysis methods based on polyhedra models carried out in I2M. Through this innovative coupling, the project will contribute:
• To characterize the geometric variability throughout the product life cycle,
• To simulate the realistic behavior of mechanism and to develop new theoretical basis for multi-physical tolerance.
The theoretical developments and digital tools implemented in the AToPAd project will systematically validate on laboratory examples, on first, and then applied on industrial mechanism proposed by industrial partners. One of the major originality of this project is that the developed tools will be shared in open source format. In addition, a CAD library of studied systems will be freely available. Finally, guidelines will be defined concerning the acuity level to be met and the associated modeling to develop according to the functional requirement and expected behavior of the system.