In 3D shape measurement systems, ones based on projecting sinusoidal fringe patterns, including phase detection profilometry and Fourier transform profilometry, are widely used due to their advantages such as simple principle, fast calculating speed, and high measuring accuracy. Through projecting sinusoidal fringe pattern to a reference plane by a projector, an original fringe pattern may be obtained. When an object to be detected is placed on the reference plane, a deformed fringe pattern may be obtained. Then a 2D absolute phase difference may be obtained through two fringe patterns, so as to obtain the 3D depth information of the object to be measured. Therefore, a phase-depth conversion and camera parameters of the measurement system need to be calibrated. But in a conventional monocular 3D shape measurement system, the periods of sinusoidal fringes on the reference plane are not fixed because of the projector and camera's non-linearity, which is caused by using common lenses. Therefore, someone proposes to use software programming to produce uneven sinusoidal fringes on a digital micro mirror of the projector, thus to project fringes with fixed periods in the measuring volume of the system. Someone else comes up with using defocusing technique, so that a binary structure fringe pattern generates an ideal sinusoidal fringe pattern. However, the system calibration process is complicated for every method above, and some parameters are very difficult to calibrate precisely, such as the distance from an optical center of a camera lens to the reference plane, the angle between an optical axis of the projector and an optical axis of the camera, and the like. While it is the calibration accuracy that determines the precision of any 3D shape measurement system.
USPTO Backgrounds
USPTO Backgrounds