Yasuyuki Ikeda

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

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.

Absolute phase analysis method for three-dimensional surface profilometry using frequency-modulated grating

The authors propose a new high-speed and accurate phase analysis and subsequent phase unwrapping method for grating projection surface profilometry. In the proposed method, a special grating pattern is used for the projection. The light intensity distribution of this grating pattern has a form of a frequency modulated sinusoidal wave. In this grating pattern, two different phase distributions are included. The frequency modulated grating, which can be generated with an LCD projector or a film projector easily, is projected onto an object. Then, nine frames with phase stepping at a regular interval for a cycle are taken by a CCD camera. From these nine pictures, the two wrapped phase distributions are analyzed simultaneously. Then, using these phase distributions, phase unwrapping is carried out at each pixel independently. The 3-D profile of the object can be reconstructed using the absolute phase distribution. Since this method is suitable for high-speed shape measurement, applications to various inspections and 3-D surface digitizing are expected.