ProModel Online Newsletter

Tips and Techniques

Conveyors

If you are considering using conveyors in your model, be sure you are familiar with how conveyors work in ProModel. Going through this little Modeling Tip will help you get started and should also help you understand your statistics if you’re only somewhat familiar with conveyors. All it takes is a little time and practice and you will soon be a conveyor expert.

Whether you have a little or a lot of information about your conveyor system, everyone should ask themselves these questions before putting conveyors in their models:

1. Will the model accomplish my objectives without using conveyors? If yes…start building! You can skip reading the rest of this article, and skip using conveyors. If no…then read on.
2. Am I modeling a powered conveyor system or is it actually a queue? Some “conveyor” systems are actually better modeled as queues.
3. Why do you want to use a conveyor? Looks better? Need to analyze the conveyor’s interaction with other factors? Just want to?
4. Will conveyors make the model too complex? Or extend the building time?

To start, when is a conveyor not a conveyer? When it is a queue. A little known fact is that you can frequently make a queue look and act like a conveyor. There are some cases in complex systems and certain applications that require using conveyors.

Next question, why might a box with a speed of 30 fpm not take 1 minute to travel down a 30 ft conveyor? It depends on the size of the box. What? The following illustration should help:

Here’s an illustration showing an 18 foot conveyor with a parcel on it, in this case the parcel is three feet long.

The next illustration shows what actually happens in ProModel. In order to calculate the actual time it will take to convey the parcel to the end, you will need to “place” the parcel ON the conveyor and subtract the length of the parcel from the conveyor length. In this case, once the leading edge of the parcel is situated ON the conveyor, the parcel only has 15 feet of travel left.

So the real time on our 18 ft conveyor is not .6 minutes, it is actually .5 minutes because ProModel calculates the distance and time from the entity’s leading edge when initially placed on the conveyor until the leading edge hits the end of the conveyor.

For some models this time difference may not be much, but consider the effects with a high speed conveyor system. Let’s say that a conveyor has to transport its product where the system produces 200 ppm (parts per minute). We would probably think to set the speed at 200 fpm for a part that is 1 ft long. However, by applying the same logic explained above, we just learned that if a conveyor running at 200 fpm, with a 1 ft part, traveling 20 ft will not take .1 min or 6 sec. The real time from leading edge to leading edge at the end of the conveyor will take 5.7 sec because the entity only traveled 19 ft. When the model is run over a long period of time, these time differences might add up and become significant.

One last tip -- if you need to take into account the time it takes to get off the conveyor, then simply enter this time in the Move Logic (the entity’s length divided by its speed) as the Move time to the next location. This applies whether the next location is an unloading station or another conveyor.

You might not be a conveyor expert yet, but you’ll have more accurate models.