FRINGE PROJECTION TECHNIQUE

Fringe Projection Technique versus Dense 3d Motion Capturing Accuracies

Fringe Projection Technique versus Dense 3d Motion Capturing Accuracies

Introduction

This technique is an extension of triangulation for out-of-plane and topography measurement. The fringe patterns are projected onto the object surface and distorted in accordance with the object height. Unlike the projection Moir´e techniques, the distorted fringe patterns are directly captured by a CCD camera and the surface height can be reconstructed from the deformed fringes, instead of using a reference grating to create fringes. The main advantage of this technique is that it is very easy to setup and does not require intensive calculation.

Digital fringe projection is based in traditional phase shifting techniques, but fringe projection has advantages in the phase-shifting accuracy, system simplicity as well as measurement speed. Phase shifting is not a specific optical hardware configuration but rather a data collection and analysis method that can be applied to a great variety of testing situation. With the fast progress in the computer technology in the past twenty years, the biggest change in all types of instrumentation is the integration of computers into the measurement systems. With the introduction of a microcomputer and a CCD camera, a series of interferograms are electronically recorded while the reference phase of the interferometer is changed. The wavefront phase is encoded in the variations in the intensity pattern of the recorded interferograms, and a simple point-to-point calculation recovers the phase

Fringe projection profilometry (FPP) is one of the leading techniques for 3D shape measurement and 3D imaging in a variety of fields. Despite the tremendous development of the FPP technique in the last two decades, there are a few practical challenges restricting the broader applications of the technique (Batlle, 2011: 827-49). For instance, the capability to measure multiple objects with complex shapes in a real-time manner is one of those challenges, and it is highly demanded by numerous applications. In this paper, a novel and robust 3D imaging system is presented, and the system is capable of providing high speed, high accuracy, and full-field 3D imaging of multiple objects. A basic FPP-based 3D imaging and shape measurement system usually contains a digital projector, a digital camera, and a computer. During the 3D imaging, a set of fringe patterns are projected onto the surfaces of the objects of interest. The surface height/depth information is naturally encoded into the distorted fringe patterns, which are captured by the camera for further processing to get back the height of 3D objects.

A single-chip Digital Light Processing (DLP) projector is utilized with the colorwheel removed; this leads to gray scale image projection for any color image. Meanwhile, a fast speed CMOS camera is employed to capture each RGB channel of the image. An external triggering circuit is developed as a microcontroller to control and synchronize the capturing process of the fast speed camera with the projecting process of the DLP projector. Therefore, three images can be obtained in each projection cycle which will significantly increases the speed of 3D ...