Optical monitoring has several positive advantages for manufacturing. Two areas of research and development of the optical system will be investigated....[ Read more ]

Optical monitoring has several positive advantages for manufacturing. Two areas of research and development of the optical system will be investigated.

In the first area, we have developed an Optical Instrument for the Thickness Feedback Control of Air Filled Membrane Products. The thickness feedback control system (shown in figure 2.1) was based on thickness measurement information for control using the proportion of two tanks that have different chemical compositions. Since the thickness measurement information was obtains from the on-line measurement of the thickness of the membrane, the first step was to develop the thickness measurement system.

We carried out the feasibility experiment for the thickness measurement of air-filled membranes using the Compact Visible Diode Laser (wavelength 680 nm). The absorption rate was about 24.1 %/mm, when the sample was a flat film that is cut out from the membrane. However, the absorption rate is about 11 %/mm, when the sample was an air-filled membrane in the original form of the product. The absorption rate is decreased from the reflection of the surface of the air-filled membrane. However, the resolution of this optical measurement system can perform 0.09 mm.

In the second area, we have also developed a new optical monitoring system used in the precision multiple-setup manufacturing process. This system can provide extremely good resolution in real time. In the preliminary setup, the system was not optimized, and the resolution of the system on average is about 2 to 3 microns. By using a thermally compensated laser source together with a pin hole spatial filtering system, we have demonstrated that lateral resolution better than 50 nm and angular displacement resolution better than 0.25 μrad is achievable with this system. We found that one of the major limiting factors was the shifting of the laser beam. A noise cancellation technique has been successfully developed to suppress this noise. Using this noise cancellation system together with a thermally compensated laser and a pin hole spatial filter in a temperature and vibration controlled environment, the feasibility of ultra high resolution (< 20 angstrom) for displacement monitoring has been demonstrated using off-the-shelf components.

Using this optical position monitoring system, we have performed repeatability experiments to observe the level of variation of placing the workpiece against a set of mechanical datum. In a controlled environment, for a sample size of 100 mm x 130 mm , we observed that the precision level of a few hundred nm can readily be achieved.