Multi-frequency and multiple phase-shift sinusoidal fringe projection for 3D profilometry

E B Li,D W Zhang,J F Chicharo,X Peng,J Q Yao,J Xi

doi:10.1364/opex.13.001561

Abstract

In this paper, we report on a laser fringe projection set-up, which can generate fringe patterns with multiple frequencies and phase shifts. Stationary fringe patterns with sinusoidal intensity distributions are produced by the interference of two laser beams, which are frequency modulated by a pair of acousto-optic modulators (AOMs). The AOMs are driven by two RF signals with the same frequency but a phase delay between them. By changing the RF frequency and the phase delay, the fringe spatial frequency and phase shift can be electronically controlled, which allows high-speed switching from one frequency or phase to another thus makes a dynamic 3D profiling possible.

Highlights

Non-contact and full-field optical surface profilometry is becoming an important measurement tool in both scientific research and industrial applications including automated manufacturing, solid modeling, computer graphics, machine vision systems, etc
In the fringe projection based profilometry, a set of fringes with a preferably sinusoidal intensity distribution is projected onto the surface to be measured and a CCD camera is positioned at a location with a viewing angle to record the distorted fringes
We have proposed and demonstrated a laser fringe projection method, which can generate fringe patterns with multiple frequencies and phase shifts

Summary

Introduction

Non-contact and full-field optical surface profilometry is becoming an important measurement tool in both scientific research and industrial applications including automated manufacturing, solid modeling, computer graphics, machine vision systems, etc. Among the proposed phase unwrapping methods, the one based on multi-frequency fringe projection can be applied to the objects with discontinuities [8, 9] In this method, multiple images are recorded at fringe patterns with different periods (from long to short) or frequencies (from low to high) in time series, and the phase at each pixel is unwrapped along the time axis. In order to realize this phase unwrapping process, a fringe projection set-up which can generate fringe patterns with variable and controllable frequencies is desirable. In a paper published in 2000, a fringe projector using an acousto-optic modulator (AOM) has been demonstrated [11] In this method, an AOM driven by two RF frequencies generates two sets of gratings inside the acousto-optic crystal and diffracts an incident laser beam into two first-order beams which are separated by a angle determined by the frequency difference of the two RF driving signals.

Experimental set-up and principle of operation

Analysis

Experiments

Conclusion