Basic investigation of noncontact transportation system for large TFT-LCD glass sheet used in CCD inspection section

Recently, thin film transistor liquid crystal displays (TFT-LCDs) have been successfully applied to desktop personal computer (PC) monitors and televisions. Higher resolution and larger mother glass sheets have been required for television displays in particular to reduce costs and improve production efficiencies. To handle the increasing resolution and mother glass size, high-speed inspection processes for detecting defects in TFT arrays using charge coupled device (CCD) cameras are becoming very important. Therefore, a noncontact transportation technique for the high-speed inspection section is necessary, to avoid damage to the glass sheet during the inspection process. In addition, high-speed CCD cameras with high resolution, large magnification and shallow focus depth are usually used in the inspection process. Accordingly, it was reported that fluctuations of less than 20 μm in the floating gap of the LCD glass sheet were required. We have used a 240 mm square LCD glass sheet as the first step of this study and an air-pad system using porous metal was investigated to support the glass sheet. The influence on the flatness of design parameters such as the nonuniformity of the permeability of the porous air pads and the appropriate combination of supply and exhaust pressures were investigated numerically for a glass sheet that was quiescently supported by the proposed air-pad system. Moreover, the numerical results are compared with experimental results to verify the validity of the numerical predictions. We found that the flatness of the glass sheet of less than 15 μm could be achieved experimentally with a floating gap of around 30 μm by using the proposed air-pad system.