Charyar Mehdi-Souzani

Scan planning strategy for a general digitized surface

As new functional requirements of products lead to the definition of more complicated shapes, reverse engineering is playing a more important role. The process consists in defining a CAD model of the object surfaces from the measurement of the real object. Reverse engineering takes advantage of new advances in noncontact measuring systems leading to a representation of the surfaces as large clouds of points. Nevertheless, scanning without path planning may affect completeness and accuracy of the measured data. This paper addresses the problem of intelligent scan planning within the context of reverse engineering. A measuring system allows us to acquire a cloud of points, which represents the first measurement of the free-form object. This incomplete and locally inaccurate cloud of points is used as a basis to generate an intelligent scan planning. A pretreatment of the point cloud is performed to determine the quality of the first scan and to find out the characteristic edges. The method relies on a voxel representation of the data. According to given thresholds of quality criteria (noise and completeness), unsatisfactory quality zones and digitizing gaps are identified. The new scan paths for an optimal digitizing are then calculated including optimal orientation search. An experimental application of the presented work is described through the digitizing of a face mask.

Farman Institute 3D Point Sets - High Precision 3D Data Sets

This article is dedicated to describe a new type of data: high precision raw data coming from the acquisition of objects by a 3D laser scanner. Supplementary Material The datasets described in this article can be downloaded from the associated IPOL web page1.

Voxel-based Path Planning for 3D Scanning of Mechanical Parts

The paper deals with an original approach to scan path planning that applies for any type of sensors. The approach relies on the representation of the part surface as a voxel map. The size of each voxel is defined according to the sensor FOV. To each voxel, a unique point of view is associated in function of visibility and quality criteria. Whatever the sensor, the method provides a set of admissible points of view to ensure the surface digitizing with a given quality.

Mesh segmentation and model extraction

High precision laser scanners deliver virtual surfaces of industrial objects whose accuracy must be evaluated. But this requires the automatic detection of reliable components such as facets, cylindric and spherical parts, etc. The method described here finds automatically parts in the surface to which geometric primitives can be fitted. Knowing certain properties of the input object, this primitive fitting helps quantifying the precision of an acquisition process and of the scanned mires. The method combines mesh segmentation with model fitting. The mesh segmentation method is based on the level set tree of a scalar function defined on the mesh. The method is applied with the simplest available intrinsic scalar function on the mesh, the mean curvature. In a first stage a fast algorithm extracts the level sets of the scalar function. Adapting to meshes a well known method for extracting Maximally Stable Extremal Regions from the level set tree on digital images, the method segments automatically the mesh into smooth parts separated by high curvature regions (the edges). This segmentation is followed by a model selection on each part permitting to fit planes, cylinders and spheres and to quantify the overall accuracy of the acquisition process.

Assistance to Automatic Digitizing System Selection for 3D Part Inspection

To perform 3D inspection, the most common digitizing system is a coordinate measuring machine (CMM) equipped with a touch trigger probe. Because of their large time consuming, a large number of industrial digitizing systems presenting different characteristics have recently emerged, but collected data quality strongly depends on the sensor technology combined with the associated displacement system. The works presented here focus on a novel approach that help users to select the most appropriate digitizing system in regard of the specification to be verified. This selection is performed in two steps: an ability selection that removes non convenient systems and a performance selection to select the system that provides sufficient data quality in the minimum time. This quality can be noise, trueness, density, depending on the specification to be verified. To store all necessary information, databases that contain intrinsic and qualified information have been developed. An example with GPS specifications is treated.© 2012 ASME

Machining Feature Recognition from In-Process Model of NC Simulation

ABSTRACTNC simulation emulates the CNC machine tool and the cutter move along its axis. It depicts the material removal to better visualize the machining process. Until now, its main goals are still confined to check an unproved NC program to avoid potential collisions, and to analyze undercuts and overcuts. In this work, by using the simulated output—the in-process model (IPM), and rebuilding a machining feature based model, applications of NC simulation are extended to establish the feedback link from CNC to CAM, which can automatically pass modifications of manufacturing engineers back through the digital chain. In cases when old CAD archives of parts are incompatible with new systems and machines, or are damaged or lost, the original CAD model is neither available nor usable, and the part program is the only data available, rebuilding the feature based model from the NC simulation is necessary. This paper proposes an approach for machining feature recognition from IPM. As per the IPM characteristics, ...

Towards a New Concept of In-Line Crankshaft Balancing by Contact Less Measurement: Process for Selecting the Best Digitizing System

Controlling the part’s balance of crankshafts are important issues for automotive manufacturers. Unbalance measurement is usually carried out using high-precision mechanical machines. The main objective of the present work is to replace mechanical measuring systems by a non-contact digitizing system, which permits the acquisition of the crankshaft surface. As the geometry to be measured presents a large variety of shapes and textures with accessibility issues, the definition of the best-suited scanning system related to geometrical and industrial constraints is a major issue.In this direction, the paper deals with the definition of a protocol based on quality indicators associated to the collected data to compare various digitizing systems. Those quality indicators are assessed thanks to simple artifacts measurement according to a specific procedure. The comparison protocol is applied to evaluate three triangulation based digitizing systems: Results allow us to identify well-adapted digitizing systems in relation to crankshaft balancing requirements.© 2012 ASME

Inline measurement strategy for additive manufacturing

Additive manufacturing takes a growing place in industry tanks to its ability to create free-form parts with internal complex shape. Yet, the quality of the final surfaces of the additive manufacturing parts is still a challenge since it doesn’t reach the required level for final use. To address this issue, it is necessary to measure the form and dimension deviation in order to plan post-process operations to be considerate. Moreover in a context of industry 4.0, this measurement step should be fully integrated into the manufacturing line as close as possible to the additive manufacturing process and post-process. We introduce in this article an inline measurement solution based on a robot combined with a laser sensor. Robot allows reaching most of the orientation and positions necessary to digitize complex parts in a short time. The use of robot for digitizing is already addressed but not for metrological applications. Robots are perfectly designed for velocity, ability and robustness but their poor positioning accuracy is not compatible with measuring requirements. The strategy adopted in this article is to provide an algorithm to generate path planning for digitizing additive manufacturing parts at a given quality of the resulting cloud of points. After a discussion about the geometric and elastic model of the robot to identify the one that answers the quality requirements, the performances of the robot are evaluated. Thus, several performances maps are introduced to characterize the behavior of the robot in its working volume. The qualification of the digitizing sensor is also performed to identify relation between digitizing parameters and the quality of final cloud of points. Using data resulting from the qualifications of sensor and robot and the parts CAD model, the algorithm allows generating path planning to ensure the final quality necessary to measure the shape deviation.

An overview of an enhanced multi-systems robotized digitizing

ABSTRACTRobots were commonly used for repetitive tasks, but to date they can handle more demanding processes like digitizing. Using a robot gives many advantages even though they still have a lack of accuracy when following a path. This paper focuses on an optimization strategy to get the best quality or/and speed for 3D digitization supported by a robot. In this way, a path planning algorithm is introduced based on the exploitation of robot and digitizing sensor performances. In order to define the robot calibration and its performances assessment, an original adapted model is investigated. An optimization step is integrated to the path planning algorithm in order to identify the best path (regarding the digitizing quality and time) among a set of admissible one. Finally the implementation of the selected path planning is carried out and the robot is monitored by an external measurement system in charge to correct this path to ensure the quality of digitizing.

Comparative Study for the Metrological Characterization of Additive Manufacturing artefacts

Additive Manufacturing (AM), also known as 3D printing, has been introduced since mid 90’ but it begins to have a broader use along last ten years. The first uses of AM process were for rapid prototyping or for 3D sample illustration due to the weak performances of mechanical characteristics of the materials available. However, even if this technology can provide answers for mechanical requirements, it will be largely used only if geometrical and dimensional characteristics of generated parts are also at the required level. In this context, it is necessary to investigate and identify any common dimensional and/or geometrical specifications of the parts generated by AM process. Highlighting singularity of AM systems should be based on the fabrication and measurement of standardized artefacts. Even if those test parts allow assessing some important characteristics of AM systems, there are still some challenges to characterize the capacity of generating freeform surfaces and features. In the literature, none of existing test parts are proposing those kind of features even if the generation of free-form surfaces is a significant benefit of AM systems. In this context, the aim of this paper is to provide a metrological comparative study on the capacity of an AM system to generate freeform parts based on an artefact.