Optimized sensor placement for active visual inspection

Abstract

This article presents an optimized sensor planning system for active visual inspection of three-dimensional manufacturing computer-aided design (CAD) models. Quantization errors and displacement errors are inevitable in active visual inspection. To obtain high accuracy for dimensioning the entities of three-dimensional CAD models, minimization of these errors is essential. Spatial quantization errors result in digitization. The errors are serious when the size of the pixel is significant compared to the allowable tolerance in the object dimension on the image. In placing the active sensor to perform inspection, displacement of the sensors in orientation and location is common. The difference between observed dimensions obtained by the displaced sensor and the actual dimensions is defined as displacement errors. The density functions of quantization errors and displacement errors depend on camera resolution and camera locations and orientations. The sensor constraints, such as resolution, focus, field-of-view, and visibility constraints, restrict sensor placement. To obtain a satisfactory view of the targeted entities of the CAD models, these constraints have to be satisfied. In this article, we focus on the edge line segments as the inspected entities. We use a genetic algorithm to minimize the probabilistic magnitude of the errors subject to the sensor constraints. Since the objective functions and constraint functions are both complicated and nonlinear, traditional nonlinear programming may not be efficient and it may trap at a local minimum. Using crossover operations, mutation operations, and the stochastic selection in the genetic algorithm, trapping can be avoided. Experiments are conducted and the performance of the genetic algorithm is presented. Given the CAD model and the entities to be inspected, the active visual inspection planning system obtains the sensor setting that maximizes the probabilities of a required accuracy for each entity. © 2001 John Wiley & Sons, Inc.