Plastics company uses vision to check ring binders

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NP Plastics, a Dutch manufacturer of injection-moulded plastic parts, is using an image-processing system to check for defects in the lever mechanics of ring binders.The fine lever mechanics of these folders also ensure that when they are full, the rings are solid and stable when closed and make it simple to open and close them without a great deal of force. The small plain plastic rollers in this closing mechanism need to be perfect to ensure they can stand up to the strain of daily office use year after year.

The challenge for NP Plastics was to check the geometry of the 5mm rings for defects and sharp edges (or burrs) at a rate of at least 600 parts per minute. To do so, the company turned to Radine BV, who with the support of Data Vision BV, Allied Vision Technologies' sales partner in the Benelux region, developed a custom solution using digital cameras to optically check the rollers for quality.

The nature of the application meant that the plastic rings pass by on the conveyor belt in random orientations. Despite this random arrangement, the system relies on two cameras that take snapshots at two different viewing angles to find defects in the geometry of the rings.

The first camera hangs over the conveyor belt and checks the rings from above. The outer and inner diameters are measured first. A second digital camera is installed on the side of the conveyor belt and checks the outer circumference of the rollers. By measuring the height of the part, defects can be identified that are not visible from the top perspective.

Both cameras are triggered by a photo cell directly over the I/O port that detects the presence of a ring on the conveyor belt. This guarantees that each individual part is detected with precision.

Data Vision recommended that Radine select two FireWire digital cameras from Allied Vision Technologies. The vertically mounted camera is a Marlin F-046B monochrome CCD camera with SVGA resolution (0.4 Megapixel). Side views of the rollers are taken by an AVT Guppy F-080B.

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