Laser interferometry is a typical representative of the highest level in the field of geometric metrology, and its accuracy can reach sub-nanometer while taking the light wavelength as a measuring scale. In this paper, we present a precisely controlled transmission structure to realize the conversion between angular and linear displacement, therefore the angular displacement can be obtained based on the high-precision linear displacement measured by the laser interferometric system. By comparing the measured angular values with the reference values, the maximum error of angular displacement measurement in this system is ± 5 arcsec, which is from the calibration certification of the National Institute of Metrology. The reference values are obtained by measuring the angular polygon with a photoelectric autocollimator, and an angular displacement measurement error of ±1 arcsec is achieved based on laser interferometric system in this paper after correcting with a series of conversion coefficients between linear and angular displacement.
In industrial manufacturing processes, the dimensional inspection of the gaps on the free-form shape parts is critical and challenging, and is directly associated with subsequent assembly and terminal product quality. In this paper, a fast measuring method for automated gap inspection based on laser scanning technologies is presented. The proposed measuring method consists of three steps: firstly, the relative position is determined according to the geometric feature of measuring gap, which considers constraints existing in a laser scanning operation. Secondly, in order to acquire a complete gap profile, a fast and effective scanning path is designed. Finally, the range dimension of the gaps on the free-form shape parts including width, depth and flush, correspondingly, is described in a virtual environment. In the future, an appliance machine based on the proposed method will be developed for the on-line dimensional inspection of gaps on the automobile or aerospace production line.
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