In-Motion Monorail Scale Problems with Hold-Back Dogs

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Nov 25, 2013

Weighing carcasses over a monorail scale comes along with far more difficulties than people sometimes realize, but with the proper application, it can provide you with very accurate weighments. One issue that comes up in plants regularly is the use of something called, “hold back dogs.”

monorail scale

Rather than the animal, “dogs”  in this case are metal stops which attach to overhead chains in order to manipulate the trolleys. Most overhead chains, including the one on our high-accuracy monorail scale, make use of push dogs. These sit behind trolleys on the chain and push them forward through the system.

monorail CTA

Hold-back dogs do the exact opposite. They keep trolleys from moving too far ahead and colliding with other carcasses. It is a useful function, but can cause some problems with monorail scales if not handled correctly.

The push dogs on our monorail scale chain are there to pull the trolley ahead of the overhead chain so it can isolate it for weighing accuracy. To do this, our chain usually needs to run faster than the overhead chain, but the hold-back dog works against this purpose.

Occasionally, when our scale pushes the trolley forward, it can run it into the hold-back dog which causes the trolley to tilt up or stop momentarily. In turn, this makes the carcass swing around, and that can throw your scale weight off if it occurs while the trolley is going over the scale. It can even wear out or break chains if it happens often enough.

That being said, we have figured out some ways to eliminate this problem.

in motion monorail scle

One of the easiest things to do, besides removing the hold-back dogs altogether, is wiring the monorail scale straight into the electronics which control the overhead chain. The scale then tries to match its speed as close as possible to the overhead chain while still taking the load. This ensures that the chain isn’t pushed too far ahead and that it doesn’t contact the hold-back dog in front of it. This also means that the scale chain will stop and start whenever the overhead chain starts and stops.

Besides that, it is possible to spread out the hold-back and push dogs, but this can hamper their functionality, especially when dealing with a whole beef carcass that needs to be supported by two trolleys.

From time to time, regular plant functions can come into conflict with new machines and processes, but we have the experience to resolve many of those issues. Let us help you with any in-motion monorail needs you might have.

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