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Precision cylindrical surfaces are very important elements in mechanical engineering applications involving sealing and guiding for precise movements. It is always important to measure the geometry of these parts to ensure smooth operation. There are several devices on the market that use tactile methods to measure the roundness of cylindrical sections. Although the metrological performance is very good, there is always a risk of scratching the measured part. Non-contact optical methods are very attractive alternatives. Deflectometry is one of those methods with great potential to accomplish this task. It is based on the indirect measurement by analyzing the distortions observed in the image of a structured pattern reflected by the measured surface. However, the application of deflectometry in precision measurement is restricted to flat or near flat surfaces. This paper presents principles and configurations for extending deflectometry to measure external and internal high quality cylindrical surfaces. In both cases the central element is a 45° conical mirror, capable of optically transforming cylindrical surfaces into planar images. An on-axis configuration allows the observation of a sequence of phase-shifted images of appropriate structured patterns reflected on the measured cylindrical surface. The patterns are formed by radial lines with sinusoidal profiles, which are rotated to promote the phase shift. An integration algorithm, suitable for periodic signals, reconstructs the geometry of cylindrical sections. As a result, it is possible to reconstruct the profile of cylindrical sections with great precision, and to determine the roundness parameters. However, it is not possible to determine the absolute radius of the measured section. The paper presents calibration considerations and the first measurements results of sections of precision pin gages. Comparisons with tactile measurements showed deviations of up to 0.07 µm in high polished cylindrical surfaces. The paper also discusses the main limitations and needed improvements. There is much work to be done before the concepts developed can be the basis of a new commercial system. However, there is great potential for the emergence of a new family of optical measurement systems.
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