Influence of CMM scanning speed and inspected feature size on an accuracy of size and form measurement

Abstract

Modern production systems requires high effectivity and flexibility with always increasing demands for precision as an imperative for more efficient components. The same apply for quality inspection providing data for feedback regulation of production processes. CMMs (coordinate measuring machines) which are flexible and universal in use yet very accurate and easy to automate are a standard mean for quality inspection. With many sensors available on the market, central fixed scanning heads with tactile scanning probes are a reference equipment for inspection of precise production of engine and transmission components. Tactile probes are right choice where very high accuracies and stability of results is required. Effectivity was allways a target in production processes and today the same pressure for effectivity and productivity is required from measuring machines, yet measurement strategies are often taken from measurement plans even 10 years old. This means that in old programs low scan speeds are used based on capability of older technologies and the approach of don´t change it when it works is common. This limits productivity of the whole quality control process. Motivation for this paper and whole research is to increase productivity and thus capacity of quliaty inspection without compromising process capability. Lack of measuring capacity is usually solved by purchase of a new machine which may not be allways necessary. Primary motivation of companies supplying these technologies is not maximum efficiency of quality inspection, which in context of spare capacities ultimately means lower sales. Aim of this article is to describe influence of scanning speed and size of inspected feature on CMMs accuracy. High-precision CMM control itself is not easy because with decreasing path radius dynamic effects of machine construction itself increase on measurement results. Accuracy of CMM measurement is then function of feature size being checked. This knowledge can be used for optimization of measurement plans in terms of productivity while maintaining sufficient measurement accuracy depending on required tolerance.

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