Making trade-Offs in system design

When my partners, and sometimes our clients raise the issue of trade-offs, it is my normal habit to challenge them and ask, ”why can’t we figure out a way to have both?”

It’s rewarding to all of us when we wrestle with the design and find a creative solution that eliminates the need for the trade-off. I will remember these work sessions as the most fun of my career.

But, in the end we really may have to determine which things we can afford, and which we cannot. We can’t always have it all.

Frequently, we can substitute a little bit of operator intervention to forego a complex or expensive automatic function.

I recall design sessions in Europe revolving around the length of the spurs on a shoe box sorter. The engineers argued, rightfully, that the similar size and weight of the boxes would give them the same trajectory coming off the sorter and that they frequently would line up along one edge of the wide spur. This would require a 20’ long spur to handle a full carton of shoe boxes – space consuming and very expensive! Faced with that prospect, the client was able to commit that the packing operators at the end of the spurs, assisted by photo cell alerts, could juggle the boxes in the spur to spread them over its width, cutting the length in half.

Sometimes, the trade-offs require choosing between the lesser of two evils. In a small system, conveyors were designed to take away totes of product from several picking areas. In order to reduce picker walk distance to the conveyor, independent lines from several zones merged prior to flowing to the pack area. The merges and controls represented more complexity than the budget would stand. A simpler single line running near a corner of each zone added 30-50’ of additional walking to off-load each batch, about 3-4 times per hour – about a 3% loss in productivity. Based on total staffing, it was judged a reasonable trade-off.

Further downstream in the same system, totes from several zones needed to be accumulated by batch and then released for sorting by order. The normal conveyor solution would have incorporated a sorter with simple 90 degree diverts into a bank of accumulation lanes – and then a slug release of a tote batch to the sorting stations.

The client began questioning the logic related to lane selection and maintaining batch integrity, and then astutely asked whether, or not the same logic might be made available to support manual sortation and release of the totes. Of course, the answer was yes. And, at current business levels, one operator would be sufficient to perform both tasks. Automation can follow when activity levels warrant.

It is important to remember when implementing a partial solution, that the first phase needs to be designed to permit a smooth transition to the final design.

Trade-offs and phasing are vital steps in system design, but I encourage you to first spend some “quality time” in the exercise of going for it all!

ABOUT THE AUTHOR

James M. Apple, Jr. is a Director in The Progress Group. Prior to co-founding The Progress Group in 1991, he was a Partner with Coopers & Lybrand's SysteCon division. During 1992-1995 he served as a Senior Systems Advisor with Vanderlande Industries, a major conveyor and systems provider in Europe.

Jim is an internationally recognized thought leader in the area of facility design and integrated distribution systems. His contributions to the improvement of distribution practices have been recognized by his receipt of the prestigious Reed-Apple Award, which is given for lifetime contributions to the advancement of the material handling profession. Jim has also received the Institute of Industrial Engineers' Facilities Planning and Design Award. He has written numerous articles and handbook chapters on warehousing and logistics operations and is a popular speaker on logistics seminar and conference programs.

Prior to SysteCon, Jim worked as an Industrial Engineer with IBM, was Supervisor of Facilities Planning for the Oldsmobile Division of General Motors and was Executive Vice President for an automotive aftermarket parts supplier. He holds B.S. and M.S. degrees in Industrial and Systems Engineering from the Georgia Institute of Technology.