Easier circuit-board assembly

Aug. 3, 2000
Printed-circuit-board assembly begins and ends when PCBs are moved out of and into carriers called magazines.

As they travel through the line, the boards may be unloaded and loaded several times before assembly is complete. But building and operating these assembly lines can be expensive. Faster, smarter, and more reliable assembly equipment is needed to improve returns. That's why engineers at Crown Simplimatic, Lynchburg, Va., designed the CIMTRAK Magazine Loader/Unloader. The new PCB loader incorporates Computer Integrated Manufacturing (CIM) software and is said to speed production, have fewer moving parts, and be safer and more reliable than previous techniques.

Traditional methods for moving magazines into loading and unloading positions typically are handled by platforms with two rows of rollers that guide the magazines into an in-feed conveyor. These platforms also rely on a plastic chain assembly driven by a dc motor. Crown Simplimatic engineers, however, designed the CIMTRAK with a gravity-feed platform that has fewer moving parts and no motor. The platform is tilted less than 2*, just enough to take advantage of gravity's pull. One hundred free-spinning rollers sit below and on each side of the platform and precisely guide magazines into the machine.

The new gravity-feed approach is said to reduce overall cost and yield a more reliable piece of equipment. And, because the gravity-feed platform sits behind the CIMTRAK system instead of alongside it, it has a smaller footprint allowing it be placed at the beginning, end, or middle of an assembly line without the need for an additional conveyor system.

By comparison, traditional conveyors that rely on dc motors with through shafts to move PCBs out and into magazines sometimes knock loose delicate chips situated on one or both sides of the boards. CIMTRAK engineers designed a new conveyor system that uses stepper motors without through shafts. It not only accommodates thin boards but is said to keep products from jamming between the belt and edge rail.

To make loading and unloading gentler, the new system uses a magnetic breakaway pusher assembly that uncouples if too much force is applied. The pusher is saddled to a pneumatic rodless cylinder guide; when the pusher encounters 5-lb resistance, it decouples from the cylinder guide.

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