Author : Dalia Nabil Mousa Mahmoud
Degree : M.Sc. Production
Title :
Shape Reconstruction
Using Structured Light Techniques
Abstract:
Shape reconstruction using structured
light has become one of the most widely used optical three dimensional scanning
methods, especially in the field of reverse engineering, where a three
dimensional model of the object is acquired. It has the advantages of being
fast, non destructive, and accurate compared to other contact scanning methods.
Various complex shaped objects can be reconstructed using structured light,
which makes it advantageous in many industrial applications. In this study, a
shape reconstruction system using structured light has been developed. The
system depends on integrating several open source codes. The purpose of the
system is to successfully reconstruct a three dimensional model of the object
being measured. The system starts by projecting stepped sinusoidal fringe
patterns on the object and acquiring their corresponding images. The phase
shift between the reference wavefront and the object wavefront is then
extracted. The extracted phase is unwrapped using the flood fill algorithm.
Finally the system is calibrated to obtain real world measurements of the
object. A single scan longitudinal calibration technique is proposed to
calibrate the structured light scanning system. A stepped calibration board is
used to calibrate the longitudinal axis instead of the traditional flat
calibration board. Each step of the board represents a different position and
therefore only a single scan is required to calibrate the measurement system.
The calibration scheme then continues as with other traditional methods. The
proposed approach neither requires a translating stage nor taking multiple
scans of the reference board at various positions. The proposed approach has a
significant effect on error reduction, is simpler to implement for in site
measurements, and is considerably faster than traditional calibration methods.
Experimental results show the reliability and effectiveness of the proposed
method, resulting in an error reduction up to 60 when compared to the
traditional method. A design of experiments study was performed to test the
impact of certain factors on the resolution of the developed system. The
considered factors include the distance between projector’s lens center and the
camera’s lens center, the normal distance between the camera and reference
plane and finally the spatial frequency of the fringe pattern used. The results
obtained showed that the developed system longitudinal resolution varies
between 0.5mm and 0.2 mm, depending on the values of the tested factors.
Further analysis of the results showed that the effect of each factor is
different, and that the most significant one is the normal distance between the
camera and the reference board. The developed system is used to reconstruct
objects with predefined geometrical features such as spheres, and objects with
a free form profile. A traditional contact measurement system was used to measure
the same test parts and the results, from both systems, were compared. The
obtained results show good agreement between both methods, which confirms the
accuracy of the developed system.
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