Plastic film is highly valued in the computer industry where plastic sheeting is used in the creation of printed circuit boards (PCBs). MicroCraft, a Japanese companyCONTROL ENGINEERING China版权所有, was challenged by a plastic sheeting manufacturer to come up with an inspection system that could find and categorize the micron-sized defects that can occur in plastic film production.
　　The manufacturer’s current method for detecting defects required an operator to evaluate an image projected onto a wall with an overhead projector. The operator would circle defects on the sheet and then carry the sheet to a microscope with a film camera attached (to photograph the defect). Next, the operator estimated the defect areaCONTROL ENGINEERING China版权所有, lengthCONTROL ENGINEERING China版权所有, and width based on other calibrated pictures and made a handwritten log entry for all the information. The operator then placed the picture in a “picture book,” in a section for the defects category. This process was time-consuming and only done sporadically, because no more than 10 samples could be completed in an 8-hour work shift.

　　Defects appear as bright spots
　　MicroCraft re-conducted the manufacturer’s original test procedure using a cross-polarized light field, along with vision and motion systems. In this method, distortion of the aligned polymer chains in the material made defects appear as bright spots. A two-step analysis was then conducted using two cameras—ones with large and small fields of view (LFOV and SFOV控制工程网版权所有, respectively) and different magnifications (LFOV: 0.3X, SFOV: 6.4X). The LFOV camera was used for initial film inspection to find defects. Operators used the SFOV camera for secondary defection evaluation, and to capture images and measurements for data storage.
　　A backlight table was covered with a polarizing sheet and placed on a 2-axis linear rail system to control the lighting and motion of the manufacturer's 8-in. diameter samples. Motionwww.cechina.cn, vision, and data collection were combined using a National Instruments PXI-7324 motion board and two PXI