Automatic pellet quality inspection by video camera.

Automatic Pellet Quality Inspection by Video Camera

What is believed to be the first electronic inspection monitor for grading resin pellet quality automatically is reportedly more accurate than traditional methods of visually scrutinizing samples of pellets or using diode-array optical analyzers to spot pellet contamination. Both methods are outmoded in this age of demanding quality control, suggests Norman Pierce, technical sales support manager of Flow Vision Inc., Little Falls, N.J., who designed the firm's new Pellet Defect Qualifier.

The P.C.Q. uses a video monitor and sophisticated image processor to view, count, and classify by size, defects in a batch of pellets. "the technology to do this has been available for years," Pierce told PLASTICS TECHNOLOGY. "It's just that no one ever put it all together into one unit." This laboratory-sized unit, which made its debut last month at the SPE ANTEC in Dallas, costs about $45,000. A production model, capable of analyzing up to 50 lb/hr of pellets and noting defect speck sizes down to 1 mm (0.04 in.) will cost about $100,000. Flow Vision expects the first field prototype to be installed in July.

HOW IT WORKS

The P.D.Q., which magnifies the pellets to 11 times their actual size, views them through a 512 X 512 pixel array video camera mounted atop an illumination envelope, under which the pellets pass on a conveyor belt fed from a bulk-loaded hopper. The illumination chamber is equipped with various colored filters to turn the pellet image on the video screen the same hue as the screen's background. This way, Pierce said, impurities in the pellets are more easily distinguishable. The unit reportedly will detect contaminants down to 0.05 mm (0.002 in.) in clear and opaque pellets.

Before reaching the screen, the image passes through an image processor which sets a digitized value on the darkest specks. The image processor then counts the number of these digitized values. At the same time, the processor has been programmed to distinguish between different-sized specks by counting the number of pixels of the matrix taken up by each defect and how many of each size are contained in a batch of pellets. The image processor can store as many as 15 different programs, Pierce said.

The system is fully automatic and after a beltful of pellets is analyzed, counts are taken, the pellets are dropped into a weighing bucket and the next batch of pellets is examined. When the bucket is full, an alarm sounds, alerting an operator to stop the machine. At the touch of a button, a printout is produced of the total defects and defects/lb for each size category. (CIRCLE 14)