Showing papers by "Joe F. Chicharo published in 2010"

Phase error correction based on Inverse Function Shift Estimation in Phase Shifting Profilometry using a digital video projector

Abstract: Fringe Pattern Profilometry (FPP) is 3D surface measuring technique based on triangulation. The utilization of digital projection in FPP system introduces significant phase distortion for Phase Shifting Profilometry (PSP), because of the nonlinear response of digital video projectors, which is referred as gamma distortion. Considering that the distorted phase has a stable function for a reference plane, this paper proposes an approach based on inverse function shift estimation (IFSE) to detect the spatial shift of the distorted phase caused by object height. This spatial shift is independent of projector's gamma distortion and accurate surface can be reconstructed based it. The simulation results show that the proposed method can almost completely eliminate gamma distortion in reconstructed surface and we obtain more than 5 times improvement in practical experiments.

Fast Quality-guided flood-fill phase unwrapping algorithm for three-dimensional Fringe Pattern Profilometry

Abstract: A fast quality-guided flood-fill phase unwrapping algorithm is proposed for real-time 3D Fringe Pattern Profilometry (FPP) system. The proposed approach consists of three steps. First, based on the phase maps acquired by phase shift profilometry (PSP) techniques, a quality map is generated according to the phase variance adjacent pixels on the wrapped phase map. According to the quality map, the phase map is divided into several parts which are categorised as either rapid phase changing areas or smooth phase changing areas. Then quality-guided flood-fill phase unwrapping algorithm is applied to rapid phase changing areas and non-guided path-following algorithm is used in the smooth phase changing area. The proposed approach is much faster than the conventional non-guided path-following algorithm, and it is more robust than the non-guided path-following algorithm. Experiments are carried out to verify the performance.

Eliminating noises contained in sensing signals from a self-mixing laser diode

Abstract: The paper studied the noise elimination methods for the signals observed from a self-mixing-laser diode (SM-LD) based sensing system. The core part of the sensing system consists of a LD, a lens and an external vibrating target. The proposed noise elimination methods are applied on both the simulated and experimental sensing signals. The results presented in the paper show the noise contained in the sensing signals can be effectively eliminated. As a consequence, the vibration trace of the target can be reconstructed with high accuracy using this sensing system.

An estimation method for feedback level factor C of a self-mixing interferometry system

Abstract: This paper presents a fast estimation method for feedback level factor C of a self-mixing interferometry (SMI) system. The reconstruction of a displacement waveform using a SMI signal needs to know a C value. However, it is difficult to maintain a constant C value during the reconstruction process. We study the features of the reconstructed displacement waveforms incorporating different pre-set C values and classify waveforms into two types. Bisection method is introduced in our method for fast estimating C value. The effectiveness of our proposed method has been verified by both simulation and experimental data.

The Height Variance Range for One Frequency Fringe Pattern Profilometry

Abstract: The upper limit on the deepest step of the surface shape that can be accurately determined is an important performance measure associated with the fringe projection profilometry. This metric is evaluated as the variance of height between two adjacent pixels on a fringe patterns reflected from the object surface. This paper presents novel results on this metric based on the Nyquist sampling theorem originally developed in the area of communication theory. Compared to existing results, we indicate that the fringe width and digital image resolution also affect the height variance range significantly. This new result could be used to increase the measurement range for projection system.

A displacement reconstruction algorithm used for optical feedback self mixing interferometry system under different feedback levels

Abstract: Displacement information of a moving target can be detected using an optical feedback self-mixing interferometry (OFSMI) system. A sensing signal observed from the OFSMI system is called self-mixing signal (SMS). The paper studies the waveform features of the SMSs and proposes an algorithm for reconstructing the displacement of a moving target. The reconstruction accuracy of the algorithm mainly depends on the locating accuracy for those characteristic points on a SMS. A set of rules for identifying those characteristic points are described in the paper. The proposed algorithm is verified by simulation signals firstly, and then applied on extensive SMSs which are obtained from the experimental set-up. The results show that the displacement of the external moving target can be reconstructed under different feedback levels.