Vehicular weight measurement while the vehicle is in motion has a significant application in traffic monitoring and weight regulation. While a conventional weighing scale requires vehicles to be sidetracked to a weighing scale, the current on-line system can provide a means of instantaneous measurement while the vehicle is moving. This would improve the throughput of heavily laden vehicles. The basis of this system is a Fiber Optic Polarimetric Sensor (FOPS) based on the principle of change in polarization of the light transmitting through the polarization maintaining (PM) fiber when subjected to external perturbation. The system is capable of static, transient and dynamic measurements. Circularly polarized laser light is coupled into the PM fiber, which is then subjected to the weight of the moving vehicle driven over it. The output from the photodetector is then displayed and analyzed using the software developed using LabView. The relationship between the weight of the moving vehicle and the wheel signature generated as vehicle passes over the pad is represented using a mathematical model. An accuracy of 86% in weight measurement of moving vehicles is achieved through this proposed system.
Micro optics characterization by use of digital holographic microscopy (DHM) is proposed recently. DHM can provide
phase image and very suitable for the quantitative mapping of transmission material with a certain refractive index.
However, it has been found that in DHM the microscope objective introduces a spherical phase curvature to the object
wave which may disturb the measurement especially for the micro-lens array. We present single lens characterization
and uniformity inspection of micro-lens array by use of a new concept DHM system developed recently. The new
concept DHM is based on a single cube beam-splitter (SCBS) configuration using an MO to provide high resolution on
the test specimen. The SCBS is put into the optical path with a small angle between the optical axis and its central semireflecting
layer. In this way, light is split into two parts when in and combined to form two holograms when out of SCBS.
For the symmetrical configuration of the beam splitter cube, the spherical phase curvature introduced by the MO can be
physically compensated during interference. Because no separated light propagation outside the SCBS, the whole system
is insensitive to vibration. As light coming out of the MO serves not only the object beam but also the reference beam, it
enables the inspection of the uniformity across a whole micro-lens array. Geometrical characterisation of the shape and
surface roughness of micro-lens is given as well as the uniformity analysis across the whole array.
A measurement system for measuring effective focal length of a microlens is presented. The system consists of a
microprocessor controlled 3-axis stage with an optical system which provides 500 times magnification for focal length
and diameter measurement. The focal length testing is carried out by single pass (transmission) approach. A point source
from halogen white light is used as the object for the measurement. A CCD camera displays the magnified image on a
computer. Focusing is performed by moving the microlens along the principal axis by manual control of a stepper motor
and observation of the image on the computer. Similarly, moving the microlens along its substrate plane and capturing
three points on its circumference gives its diameter. The co-ordinates of the 3-axis stage and diameter are displayed
separately on dot-matrix LCD panel. Anti-backlash mechanisms are employed on all axes, each with a positioning
resolution of 1 μm.
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