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Sequential measurements method for moving surfaces profiling Gazzarri, Javier Ignacio


Surface profiling is an important need in many industrial and scientific applications. Lumber manufacture quality control is a typical example. The simplest way to measure surface height profile is to make a series of measurements with a displacement sensor while relatively moving the specimen and sensor in a straight line perpendicular to the measurement direction. The drawback to this method is that deviations from straight-line motion cause errors that are indistinguishable from measured surface shape. In many cases, linear motion of the required accuracy is not practicable in industrial conditions. The state of the art procedure to monitor surface quality is thickness measurement, which is insensitive to rigid motion. However, it cannot separately identify the surfaces each side of the product, very often machined by different tools. This work describes a novel method for measuring surface height profile in presence of relative motion between the piece and the sensor and on two sides independently. This is very useful for maintenance purposes because it constitutes a fast and direct way to monitor tool performance online. The procedure involves using multiple sensors operating along a line in the direction of the object motion. The central idea of the proposed method is the observation that surface height features appear in delayed sequence as the specimen moves sideways relative ,to the sensor array. However, any relative motions, either vertical or rotational, appear simultaneously at all sensors. The proposed equations constitute an inverse problem, and fitting methods of Inverse Theory are used to separate the delayed and simultaneous components of the measurements, from which the surface height profiles can be reconstructed. The proposed equations were applied on an experimental conveyor with several laser sensors on different scanning configurations. Surface calculations adequately met accuracy requirements of lumber inspection standards. The proposed method is capable of profiling two sides of an object, separately and independently of relative motions between the sensors and the surfaces. If parallel lines are scanned on the same side of the object, information about overall twist is also obtained.

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