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 company, 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 area, length, 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控制工程网版权所有,” 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 fieldwww.cechina.cn, along with vision and motion systems. In this methodwww.cechina.cn, 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, respectively) and different magnifications (LFOV: 0.3XCONTROL ENGINEERING China版权所有, SFOV: 6.4X). The LFOV camera was used for initial film inspection to find defects. Operators used the SFOV camera for secondary defection evaluationCONTROL ENGINEERING China版权所有, 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. Motion, vision, and data collection were combined using a National Instruments PXI-7324 motion board and two PXI