Laurent Sabourin

Optimal selection of machining direction for three-axis milling of sculptured parts

In the field of free form surface machining, CAM software allows management of various modes of tool-path generation (zig-zag, spiral, z-level, parallel plan, iso-planar, etc.) leaning on the geometry of the surface to be machined. Various machining strategies can be used for the same shape. Nevertheless the choice of a machining strategy remains an expert field. Indeed there are no precise rules to facilitate the necessary parameter choice for tool-path computation from analysis of the numerical model of a part and the quality requirements. The objective of this paper is to provide a method to assist in the choice of the machining direction for parallel plane milling of sculptured parts. The influence of the tool-path on final quality according to the intrinsic geometrical characteristics of the latter (curves, orientation) was studied. Directional beams are introduced and defined from the local surface parameter. Finally, a methodology to optimize machining time while guaranteeing a high level of quality was developed and applied to examples.

OMEGA, an expert CAPP system

This article presents the validation of a part analysis method for the creation of a process-planning system for automobile prototype activity at the PSA group. The methodology presented is founded upon the division of the problem into two semi-separate sub-fields. The first consists of automatically defining the operation sequences of machining features using production rules. The second one defines the sequencing of machining operations in set ups, founded upon a constraint planning strategy. The methods developed in this article have been implemented as an expert system named OMEGA.

Performance Criteria to Evaluate a Kinematically Redundant Robotic Cell for Machining Tasks

Machine tools and robots have both evolved fundamentally and we can now question the abilities of new industrial robots concerning accurate task realization under high constraints. Requirements in terms of kinematic and dynamic capabilities in High Speed Machining (HSM) are increasingly demanding. To face the challenge of performance improvement, parallel and hybrid robotic architectures have emerged and a new generation of industrial serial robots with the ability to perform machining tasks has been designed. In this paper, we propose to evaluate the performance criteria of an industrial robot included in a kinematically redundant robotic cell dedicated to a machining task. Firstly, we present the constraints of the machining process (speed, accuracy etc.). We then detail the direct geometrical model and the kinematic model of a robot with closed chain in the arm and we propose a procedure for managing kinematic redundancy whilst integrating various criteria. Finally, we present the evolution of the criteria for a given trajectory in order to define the best location for a rotary table and to analyze the manipulators stiffness.

Interaction modeling in the grasping and manipulation of 3D deformable objects

Robotic grasping has been extensively studied in the last two decades. Most of the research in this field has been dedicated to rigid body grasping, and only a few studies have considered the case of deformable objects. Nevertheless, the robotized grasping of deformable objects has many potential applications in various areas, including bio-medical processing, the food processing industry, service robotics, robotized surgery, etc. This paper discusses the problem of modeling interactions between a multi-fingered hand and a 3D deformable object for robotic grasping and manipulation tasks. Our work presents a new strategy for modeling contact interactions in order to define the relationship between applied forces and object deformations. The mechanical behavior of the deformable object is modeled using a non-linear anisotropic mass-spring system. Contact forces are generated according to the relative positions and velocities between the fingertips and the boundary surface facets of the deformable object mesh. This approach allows reducing the number of nodes while ensuring accurate contact modeling.

Model-based strategy for grasping 3D deformable objects using a multi-fingered robotic hand

This paper presents a model-based strategy for 3D deformable object grasping using a multi-fingered robotic hand. The developed contact model is based on two force components (normal force and tangential friction force, including slipping and sticking effects) and uses a non-linear massspring system to describe the object deformations due the mechanical load applied by the fingers of the robotic hand. The objectfinger interaction is simulated in order to compute the required contact forces and deformations to robustly grasp objects with large deformations. Our approach is able to achieve this by using a non-linear model that outperforms current techniques that are limited to using linear models. After the contact forces computed by the simulation of the contact model guarantee the equilibrium of the grasp, they will be used as set-points for force-controlling the closing of the real fingers, and thus, the proposed grasping strategy is implemented. Two different objects (cube and sphere) made from two soft materials (foam and rubber) are tested in order to verify that the proposed model can represent their non-linear deformations and that the proposed grasp strategy can implement a robust grasp of them with a multi-fingered robotic hand equipped with tactile sensors. Thereby, both the grasping strategy and the proposed contact model are validated experimentally.

Redundancy-based optimization approach to optimize robotic cell behaviour: application to robotic machining

Purpose – The robot offers interesting capabilities, but suffers from a lack of stiffness. The proposed solution is to introduce redundancies for the overall improvement of different capabilities. The management of redundancy associated with the definition of a set of kinematic, mechanical and stiffness criteria enables path planning to be optimized. Design/methodology/approach – The resolution method is based on the projection onto the kernel of the Jacobian matrix of the gradient of an objective function constructed by aggregating kinematic, mechanical and stiffness weighted criteria. Optimized redundancy management is applied to the 11-DoF (degrees of freedom) cells to provide an efficient placement of turntable and track. The final part presents the improvement of the various criteria applied to both 9-DoF and 11-DoF robotic cells. Findings – The first application concerns the optimized placement of a turntable and a linear track using 11-DoF architecture. Improved criteria for two 9-DoF robotic cells...

Design Process Modeling of Process Planning for Flexible Lines Based on Conceptual Graphs and Design Rules. Applied to Cylinder Head Machining

Process planning for mass-produced parts in the manufacturing industry requires a long and critical approach as both product/process data interaction and technical and cost-effectiveness parameters are crucial. Within the RENAULT Powertrain Division, the scope of our research work is to define process plans for prismatic parts machined on flexible production lines. A process plan is the outcome of a constraints analysis based on quality, cost, lead time, strategy and innovation goals. The first step of our work consists in identifying and formalizing any constraints: manufacturing process constraints (machining, assembly, etc.), product geometry, functional constraints (camshaft bearing lines, combustion face, etc.) and production constraints (volume, mix, etc.). Using conceptual graphs associated with the Design Rules methodology enables us to view precisely several functional conditions to be met for a product. One of the key features of the Design Rules methodology is to provide feasibility areas used to assess whether a product may or not be machined on a production line. In addition conceptual models are also used to identify and set procedural rules to limit technical risks and re-use already developed practical skills.

Analysis of the human arm gesture for optimizing cutting process in ham deboning with a redundant robotic cell

Purpose – The mechanization of the meat cutting companies has become essential due to the lack of skilled workers and to working conditions. This paper deals with the analysis of human gestures in order to improve the performance of a redundant robotic cell. The aim is to define optimization criteria linked to the process and the human gesture analysis to improve the cutting process with a redundant robotic cell. Design/methodology/approach – This paper deals with an optimized path planning of complex tasks based on the human arm analysis. The first part details the operators manual work. The robotized cutting strategy using bones as a guide associated with an industrial force control leads to the tasks redefinition. Thus, the analysis of the arm during the tasks is presented. With a robotic model, the authors evaluate the relevance of two criteria (kinematic and mechanical) that the operator naturally manages. These criteria are used to improve the robotized cutting process by using redundancy. Simulati...

Improving the capability of a redundant robotic cell for cast parts finishing

Purpose – Precision aluminium moulding makes possible the production of large‐size, complex and high‐technology cast parts. However, industrial requirements linked to economic and safety reasons call into question the manual performance of finishing operations. The purpose of this paper is to enhance industrial robot applications by using vision and redundancy optimization to improve their capability.Design/methodology/approach – After having presented the concepts associated with machine and kinematics capability, the paper first describes the finishing constraints related to the process and the study of inaccuracy factors. Adjusting the trajectory by vision minimizes some inaccuracy factors but does not take into account the structure loading. Therefore, the authors present the optimization, kinematics and precision criteria as well as the multi‐objective method developed by integrating the loading aspect. This method has been verified by simulation and the results validated on industrial parts.Findings...

Directional Beam Based Approach Applied to the Choice of Machining Direction for a Sculptured Part

Within the framework of the manufacture of sculptured parts in three axes (foundry moulds, plastic injection and stamping die), CAD/CAM software currently offers a broad range of operations associated with increasingly powerful tool-path generators. However, there is no methodological guide that facilitates an optimized choice of the machining process (roughing, finishing) and the adjustment of the various parameters of the tool-path generators. The objective of this research is to provide a tool to assist in the choice of application of machining strategies for sculptured parts. We decided to focus on the machining strategy choice in the finishing process. This operation determines the final quality of the part. The objective of this work is to provide a methodology for machining strategy choice in the finishing process based on the criteria of surface roughness.