Gad N. Abenhaim

A Novel Approach for the Inspection of Flexible Parts Without the Use of Special Fixtures

In a free state, flexible parts may have different shapes compared to their computer-aided design (CAD) model. Such parts may likewise undergo large deformations depending on their space orientation. These conditions severely restrict the feasibility of inspecting flexible parts without restricting the deformations of the part and therefore require dedicated and expensive tools such as a conformation jig or a fixture to maintain the integrity of the part. To address these challenges, this paper proposes a new inspection method, the iterative displacement inspection (IDI) algorithm, that evaluates profile variations without the need for specialized fixtures. This study examines 32 models of simulated manufactured parts to show that the IDI algorithm can iteratively deform the meshed CAD model until it resembles the scanned manufactured part, which enables their comparison. The method deforms the mesh in such a manner so as to ensure its smoothness. This way, neither surface defects nor the measurement noise of the scanned parts are concealed during the matching process. As a result, the case studies illustrate that the methods error essentially only represents the scanned parts measurement noise. The inspection results, therefore, solely reflect the effect of variations from the manufacturing process itself and not the deformation of the part.

A virtual fixture using a FE-based transformation model embedded into a constrained optimization for the dimensional inspection of nonrigid parts

Virtually mounting nonrigid parts onto their fixture is proposed by researchers to remove the need for the use of complex physical inspection fixtures during the measurement process. Current approaches necessitate the pre-processing of the free-state nonrigid parts point cloud into a suitable finite element?(FE) mesh and are limited by the use of the boundary conditions setting methods available in FE software. In addition to these limits, these approaches do not take into account the forces used to restrain the part during the inspection, as commonly mandated for aerospace panels. To address these shortcomings, this paper presents a virtual fixture method that predicts the fixed shape of the part without the aforementioned drawbacks of current approaches. This is achieved by embedding information retrieved from a FE analysis of the nominal CAD model into a boundary displacement constrained optimization. To evaluate the proposed method, two case studies on physical parts are performed using the proposed virtual fixture method to evaluate the profile and assembly force specifications of each part. The virtual fixture method allows for the inspection of nonrigid parts.It does not necessitate the pre-processing of the point cloud into a FE mesh.It takes into account the parts specification limiting the restraining forces.It infers the parts structural behavior from the FE model of the nominal CAD.Two case studies on physical parts are performed.

Aerospace panels fixtureless inspection methods with restraining force requirements; A technology review

Aerospace panels are commonly restrained on complex inspection fixture jigs during the measurement process. Forces used to restrain the parts are also monitored as mandated by thier functional requirements. Given the difficulties in measuring these types of parts, this paper reviews the available fixtureless inspection methods with a focus on the challenges of their implementation, and their aptitude to be used to estimate the profile and the necessary restraining forces of an aerospace panel. To perform this investigation, finite element analysis is used to predict the constrained shape of four (4) simulated free-state aerospace panels, with two different type of boundary conditions, in five scenarios. From those analyses, the importance and limits of current finite element boundary setting methods embedded in fixtureless inspection methods for nonrigid parts are highlighted.

A Finite-Element Boundary Condition Setting Method for the Virtual Mounting of Compliant Components

Using finite-element analysis (FEA) to numerically mount compliant components onto their inspection fixture is an approach proposed by researchers in the field of computational metrology. To address the shortcomings of the underlying principle of current methods, this paper presents a boundary displacement constrained (BDC) optimization using FEA. The optimization seeks to minimize the distance between corresponding points, in the scanned manufactured part and the nominal model, that are in unconstrained regions. This is done while maintaining that a distance between corresponding points in constrained regions (i.e., fixing points) remains within a specified contact distance. At the same time, the optimization limits the magnitude and direction of forces on boundary. In contrast to the current methods, postprocessing of the point cloud is not required since the method uses information retrieved from the FEA of the nominal model to estimate the manufactured part’s mechanical behavior. To investigate the performance of the proposed method, it is tested on ten (10) free-state simulated manufactured aerospace panels that differ in their level of induced deformation. Results are then compared to those obtained using the underlying principles of current methods.