Optimised multi-camera systems for dimensional control in factory environments

Abstract

As part of the UK's Light-Controlled Factory project, University College London aims to develop a largescale multi-camera system for dimensional control tasks in manufacturing, such as part assembly and tracking. Accuracy requirements in manufacturing are demanding and improvements in the modelling and analysis of both camera imaging and the measurement environment are essential. A major aspect to improved camera modelling is the use of monochromatic imaging of retro-reflective target points, together with a camera model designed for a particular illumination wavelength. A small-scale system for laboratory testing has been constructed using eight low-cost monochrome cameras with C-mount lenses on a rigid metal framework. Red, green and blue monochromatic LED ring illumination has been tested, with a broad-band white illumination for comparison. Potentially, accuracy may be further enhanced by the reduction of refraction errors caused by a non-homogeneous factory environment, typically manifest in varying temperatures in the workspace. A refraction modelling tool under development in the parallel EU LUMINAR project is being used to simulate refraction in order to test methods which may be able to reduce or eliminate this effect in practice.

An SI-traceable multilateration coordinate measurement system with half the uncertainty of a laser tracker

“…However, the laser trackers are sensitive to temperature gradients, a situation that can be seen outdoors or in harsh industrial environments such as a workshop without air conditioning. These gradients can induce beam deflections, and so errors in the angle measurements of the laser tracker, which can lead in some cases to position errors of several tens of micrometers as reported in [11,12]. Thus, for certain operations, the multilateration technique is more suitable as the length measurements are less susceptible to beam refraction than are the angular measurements: the knowledge of the angles is no longer necessary, only the distance data are required.…”

Overview of Optical Digital Measuring Challenges and Technologies in Laser Welded Components in EV Battery Module Design and Manufacturing

“…Industrial photogrammetry is a passive method where the image is processed without active illumination. The object is being photographed from different angles and triangulation is used to calculate the point cloud [51]. The system functions using multiple fixed cameras, repeatability of the measurements is reported to be ±0.02 mm with real production parts.…”

Calibration Procedure of a Multi-Camera System: Process Uncertainty Budget

“…Perez-Cortes et al [ 10 ] also follows a similar strategy, but instead of using a pointer, a sphere is used in 16 positions, and it is solved through a set of camera projections of the epipolar lines. Robson et al [ 11 , 12 ] carried out a photogrammetric calibration procedure (bundle adjustment) through the Manhattan Vision Metrology System (VMS) pattern to solve intrinsic parameters, extrinsic parameters, and 3D coordinates in one go. As future lines of this work stand out, the evaluation of the multi-camera system using one or more calibrated scale bars in various orientations within the common intersection volume for all the cameras and the evaluation of the performance specifications through the VDI/VDE 2634 [ 13 ] are performed.…”