INTRODUCTION
Optical disc usage and application is not only extensively used but growing
in popularity and importance. Currently the number of optical discs manufactured
the injection method namely CD-ROM and Video CD contribute to about 70-80%
of the total volume optical discs produced. The future of this industry
depends heavily on the quality on the finished product. The quality of
the finished product is so closely knitted and integrated with the quality
of the master plate. For this reason it became vitally important in the
production of high density optical discs to find an easy, watertight, successful
and cost and time effective method or system to monitor, measure, observe
and analyze the quality of the master plate on an ongoing basis. The conventional
method in a production environment to detect defects on a master plate
of an optical disc is to expose the plate to a yellow light and observing
whether the light fields reflect any distorted images notable to the naked
eye. Key points are examined using a microscope. Because of the huge surface
area that has to be inspected (up to 14” diameter for CD-ROM and video
CD) it? not possible for a technician to conduct
in-line testing of all the master plates by microscope. Most techniques
used to observe and evaluate the micro-composition of the surface provide
a earnest description of the master plates outlines. One can also observe
contamination object with a microscope, CCD camera or by using a computer
to scan the dimensions of the emulsion or to detect micro-particles of
a microstructure.[4]
The optical disc manufacturing process is strictly evaluated on the
criteria of micro-particle contamination. Managing the sources, detecting,
analyzing and monitoring the contamination economically and effectively
and selecting cleanroom material are vital important ingredients for success
of this industry[5]. The shapes and particles in a cleaningroom are classified
in four category types by Alvin Lieberman[6]
a. Sphere type: The diameter of these particles is from 0.01
to 300 µ m, and the quantity about
10% of all particles.
b. Cube type: The diameter of these particles is from 0.11 to
1000 µ m, and the quantity about
30% of all particles.
c. Fiber type: The diameter of these particles is from 0.1 to
500 µ m, and the quantity of these
particles is about 15% of all particles.
d. Flake type: The diameter of these particles is from 0.1 to
100 µ m, and the quantity is about
45% of all particles.
The instrumentation for counting particles[7-8], detecting and identifying
the particle composition[9-10] comprise of optical and photo voltage real-time
monitoring measurement techniques that are essential to manage various
and divers cleanroom systems.
In this paper a mechanism having a reflecting surface and used for inscribing
transmitted information on a optical master disc plate in the manufacturing
process. The aforesaid device or mechanism comprises of the following:
* A microscope and frame.
* A table x-y able to supporting a optical disc.
* Measurement and control system for determining defects during the
operation.
Fig.1 highlights a block diagram of automated, evaluating device set-up.
The lamp emitted light energy is focused through the master plate onto
the CCD camera at a plurality of pre-selected wavelengths in the red light
range of 580-680 nm. The illumine wavelength is selectively controlled
by a plurality of filter elements carried(transmitted) by the respective
peripheral apertures, having transmission characteristics corresponding
to the plurality of pre-selected wavelengths.
Fig. 1 The block diagram of the set-up
In conjunction with the aforesaid equipment we use a digital image processing
technique and a recognition (detection) neural network algorithm as proposed
by B.H. and M.R.K. [11] the shape characteristics of defects on an optical
disc.
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