Proceedings PaperScratch And Dig Measurement - A Way Ahead
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Although a worrying problem ever since optical components were first produced, the measurement of imperfections on optical components has become more acute in the last few years due to an increase in international trade, the more widespread use of laser optics and the trend towards automation in component production. Quite apart from their functional effect on certain classes of component, visible signs of surface damage have a direct impact on perceived quality and therefore customer acceptability of the product. This paper reviews previous attempts to quantify scratches and digs in relation to a variety of different so-called standard artefacts and discusses the extent to which these attempts have met with the approval of quality engineers and customers and are therefore likely to form a satisfactory basis for embodiment in an international standard. The results of recent surveys, supported by laboratory trials, conclude that all current national standard procedures dealing with surface imperfections produce an uncertainty of measurement in excess of levels normally regarded as acceptable by quality engineers. The reasons for this large uncertainty of measurement are discussed and a suggestion made for a new approach to the measurement of scratches based on photometric rather than geometric considerations. The reactions of potential users and the results of measurements of uncertainty using this approach indicate that it has much to offer both as a means of training inspectors and as an inspection tool for workshop use.