The development of a system of automatic inspection for surface material defects

Abstract

A prototype has been developed with a view to automating the visual inspection of a range of ring-shaped components. The types of defect which occur in these components are described, and criteria are developed for defect detection which imply 100 micron diameter pinhole porosity as the limit of required resolution. Potential non-destructive testing techniques are reviewed and an opto-electronic technique selected as appropriate. Opto-electronic scanners are discussed and a linear solid-state photodiode array incorporated in a line scan camera is chosen as a promising solution. The use of this device is described, including : illumination,optics,analogue and digital electronic processing, and interfacing to a microprocessor. Strategies for isolating defect information from the many other variations in the signals are discussed. At the system component interface, a new model is developed of the scanning patterns of an optical array on a moving inspected surface. This leads to a description of sensitivity variations over scanned areas and a means of predicting dynamic phenomena from static measurements at the limits of the array resolutions. The technology involved was entirely new to the company which sponsored the project. The importance of the proper treatment of innovation in a project such as this is discussed in terms of the suitable presentation of costs, and convincing demonstrations.