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Devices automate with intermittent motion.

Bill Harris has a better idea for mixing intermittent indexing motion on a continuously moving conveyor.

Formerly an engineer at General Electric's lamp manufacturing operations at Nela Park, OH, and a sometime machine shop owner, Mr Harris has designed and patented devices that produce continuous and intermittent motion on the same chain carrier. He calls the mechanical devices "Overton engines" and says they're the building blocks of motion automation, bridging the gap between continuous motion systems and indexing machines. Applications for the devices range from painting lines to chain-on-edge material handling for metal fabrication.

The objective of combining linear and rotary motion on the same continuous chain or conveyor is straightforward enough. When the chain, which is always continuously moving on one side, stops on the other side, an assembly operation can be performed. Paint or glue can be applied, for example.

Once in motion again, the chain goes back to being a straight-line indexer. The part can be routed through a furnace and heated, for example, on its way to an assembly point. Or curing can take place. Some examples of how combining linear and rotary mechanical motion might work include:

* A 1/4" steel sleeve about the size of a cigarette and standing vertically on a 6" center could be stopped in front of an adhesive applicator.

* A 2 1/2" thermoplastic part on 4 1/2" centers nested at the end of the intermittent-motion section of chain could be conveyed through a warming oven at constant speed and back to the straight-line indexer for assembly with another part.

Mr Harris has designed two very different mechanisms to create exactly the same motion: a compound cam mechanism in which the center of the cam is on a linear slide and the cam follower roller(s) is fixed; and a multiple-cam driver that generates combined linear and rotary movement of a second shaft.

The compound cam mechanism is the simpler of the two devices. It integrates into an existing continuous-motion conveyor and is powered by that chain. The chain wraps around a first idler pulley, then around a sprocket that rotates and oscillates with the compound cam. From there, the chain goes to a sprocket that is free to rotate and moves linearly with the compound cam shaft.

This section of the chain stops, dwells for an exact time, and then smoothly advances a precise distance. According to Mr Harris, the indexing of the section of chain and nests can be any length. The dynamic forces required to accelerate and decelerate this section of chain are reflected back into the parent chain system. The chain then wraps around a second, fixed idler sprocket, and the chain coming off of it is moving at the initial constant velocity.

The Overton compound cam device is well suited to chain-on-edge conveyors. A section of chain can be brought to a stop for processing or for automatic parts loading and unloading. No additional motors are required, and existing systems can be retrofitted with the device.

The second Overton engine, a combined linear and rotary motion device, is used to generate intermittent motion of a section of the conveyor when the sprocket size of a chain-on-edge conveyor is large with respect to the length of advance of the chain.

The multiple-cam driver, which usually becomes the main drive for the conveyor system, generates combined linear and rotary movement of a second shaft to drive a carousel conveyor where the nests and chain go around only one pair of sprockets. The cams come in a series of five sizes, each 50% larger than the last, in diameters from 1/2" to 3".

Multiple-nest indexing, part placement, and unloading operations take place on one side of the carousel. Process operations would be done on the continuous-motion side of the carousel conveyor. This type of conveyor is particularly well-suited for processes like lamp-making, where parts can be automatically loaded and aligned at fixed tooling positions and then processed at constant speed through other operations.
COPYRIGHT 1993 Nelson Publishing
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Copyright 1993 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Manufacturing Solutions
Publication:Tooling & Production
Date:Apr 1, 1993
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