Three-dimensional shape measurement based on digital fringe projection and phase-shifting techniques

In this research, we developed a novel 3-D shape measurement system based on digital fringe projection and phase-shifting techniques. The use of these techniques significantly improves the flexibility, speed, and accuracy of 3-D shape measurement.; In this new system, software-generated fringe patterns are projected through a digital projector. Images captured by a CCD camera are sent to a computer to calculate the phase map. An additional line is projected, and its image is processed to obtain the absolute phase map, from which a phase-coordinate conversion model is used to calculate the 3-D coordinates. This system is calibrated by a two-step method. The unknown parameters are measured directly to provide initial values for further parameter estimation. Then, an iteration algorithm is used to refine the parameters based on this conversion algorithm. Some experimental results are presented to show the performance of the system and the effectiveness of the calibration technique.; A new 360° reconstruction concept is also proposed. The object mounted on top of a rotation stage is rotated twice and measured patch by patch. The rotation axis calibrated by the use of a calibration board and refined by an iteration algorithm is used to set up the rotation stage coordinate system in which the patches are rotated to their original positions to be connected to form the 360° shape. To improve the 360° reconstruction results, the measured patches of a cylindrical object are resampled and an iteration algorithm is used to optimize the rotation axis.; Main error sources are analyzed and a new portable system is designed with improved performance. Different phase-shifting algorithms are compared. To reduce the effect of the nonlinearity error, a new phase-shifting algorithm called double 3-step algorithm is developed. An error compensation algorithm is used to reduce the other remaining errors by compensating for the errors of the measured coordinates directly.; Currently, the accuracy of this 3-D shape measurement system can reach about 0.2 mm in the measurement volume (approximately 300 x 250 x 200 mm). With this system, a part can be measured with over 1.6 million points within 25 seconds.