Three-dimensional surface profile measurement of a moving object by a spatial-offset phase stepping method

Abstract

This study proposes a new method for measuring the 3-D surface profile of an object moving at constant speed. A sinusoidal grating pattern is projected on a moving object. Then, grating patterns that are deformed according to the profile of the object are acquired by three linear array sensors. Since a linear array sensor records light intensity along an original grating line, the resultant image forms a fringe pattern that represents the profile of the object. Using three images obtained by the three linear array sensors, the phase distribution of the fringe pattern is calculated by a phase stepping method without any phase stepping devices. Consequently, the profile of the moving object can be evaluated from the phase of the fringes, since the value of the phase is simply proportional to the height of the object. Experimentation demonstrates that the accuracy is about 4.3% for the wrapped phase range of 2π rad with a speckle pattern present. The proposed method can be used for inspection of moving objects such as products on an assembly line.