First Thoughts
  By Dan Gilmore - Editor-in-Chief  
  July 6, 2007  

Bees, Order Picking and Self-Organizing Logistics Systems

Gilmore Says:
The concept is especially applicable for anyone using pick-to-light, as the hand-off between workers would be totally seamless. There would be a bit more overhead in that hand-off with other picking technologies, but Bartholdi says the benefits apply there as well.

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I was on my way recently to give a presentation at the Manhattan Associates User Conference when I passed a sign for an intriguing presentation: “Self-Organizing Logistics Systems.”

It was offered by Dr. John Bartholdi of The Logistics Institute at Georgia Tech, and unfortunately scheduled at the same time as my session. But I left a card with the host and told him I’d like to speak later with Dr. Bartholdi, and he was soon gracious enough to contact me.

So what is “self-organizing logistics?” Well, it is has something to do, literally, with the birds and the bees, or I guess the bees and the ants. Somehow, Dr. Bartholdi observes, bees in the hive are able to run incredibly effective “logistics” operations, without the benefit of software, pick-to-light systems, or even RFID. In fact, they don’t even have a boss. The queen gets treated royally, but she doesn’t tell the drones what to do.

So how do bees do it? As best we can tell, by self-organizing, based on simple signals from surrounding bees. “Each bee or ant in a colony follows some simple rule” Bartholdi told me. “Together, they achieve tremendous organization and effectiveness on a larger scale.”

Somewhere along the way, Bartholdi got to wondering just whether there were applicable self-organizing concepts for supply chain and logistics systems. Turns out there are, and that Bartholdi has been writing about them since the mid-1990s. I’m slightly embarrassed to only be learning about the concept right now.

The most clear and proven opportunity to utilize the concept is in order picking in a distribution center, specifically for “case” or especially “piece” picking (the picking of individual items into a carton or tote).

It’s always a high cost operation, and companies have tackled it with lots of technology and process, from “cluster picking” to zone picking, dynamic zone picking, Labor Management Systems with engineered standards, pick-to-light, now voice, and more.

All those have a place, and can add value, but are often based on a flawed concept, says Bartholdi: these “work content models” (zones, etc.) are “almost always wrong in practice – it’s just a guess.” Because workers operate at different speeds, both naturally, and at any given point, they become bottlenecks, and slow down the effectiveness of the whole.

The answer: self-organization: Forget zones, whether static or dynamically assigned. Each workers just does the next thing they are supposed to do (more in a moment), and adjacent workers respond. Voila – the line balances itself, and productivity and throughput are substantially increased.

“The concept is too darn simple – I can’t make any money on it!” Bartholdi jokes.

It works like this: Each worker starts down a pick line, at the speed they can accomplish given their skill and the difficulty of the next pick. When the last worker finishes his pick at the end of the pick line, he or she walks back upstream to take over the work of their predecessor, who walks back and takes over the work of his or her predecessor and so on. This continues until, after relinquishing his picks, the first worker walks back to the start to begin a new set of orders/picks.

If  you also then sequence the workers from slowest to fastest, Bartholidi calls the system a "Bucket Brigade," and the workers will spontaneously gravitate to the optimal division of work so that throughput is maximized.

Let me try to paint the picture another way. When the last/fastest worker gets done, he/she simply walks upstream until he/she encounters the picker behind them, and takes over any picks from wherever the hand-off occurred. That worker does the same, etc., until the first picker returns to the beginning of the line.

OK, like me you are probably saying “Has it been tried? Does it work?” Apparently Yes to both questions. Bartholdi’s Bucket Brigade web site lists a number of successes. Like many things, it seems to have found something of a home in one industry segment, that being music/video/books.:

  • McGraw-Hill: Order-pickers in distribution centers
  • The MusicLand Group: Order-pickers
  • Time Warner Trade Publishing/Little, Brown: Order-pickers
  • Bantam-Doubleday-Dell Distribution: Order-pickers
  • Harcourt-Brace: Order-pickers
  • Blockbuster Music: Order-pickers

Drug store chain CVS apparently achieved a 34% productivity increase from the Bucket Brigade approach.  “Most companies see a 25-50% gain,” Bartholdi told me.

As may be clear, the concept is especially applicable for anyone using pick-to-light, as the hand-off between workers would be totally seamless. There would be a bit more overhead in that hand-off with other picking technologies, but Bartholdi says the benefits apply there as well. There are some limitations – you need fairly dense picks/higher volumes to really see the benefits. But then again, that’s where costs are high.

The bigger question may be: Does this concept have applicability in the supply chain anywhere outside order picking?

It appears clearly yes in certain assembly systems in manufacturing. I don’t have space to detail it here, but there is some information, and one interesting research paper from Australia, on this topic on the web site. Some may suggest there are some similarities to the Toyota Sewing System (TSS), and there are, but TSS traditionally involves static zones, and didn’t incorporate the idea of sequencing workers from slowest to speediest.

Dr. Bartholdi is also looking at other logistics processes, such as shipping that involves multiple legs. While he believes the concept would prove valuable there, the realities of trying to get disparate parties to coordinate like this may be too daunting. But it could work for more closed loop systems, like military logistics. He is looking at other possibilities. In some cases, he believes such as system could work as well or better than if you had detailed visibility and could “optimize” everything.

“Bucket Brigades are a pure pull system,” Bartholdi added. “Insects know nothing about push.”  

That’s something worth thinking about. I also think there is some money here after all for a few bright logistics consultants….

Do you have any experience implementing Bucket Brigades? What were your results? How does this concept strike you? Do you see any other opportunities for using it in supply chain?

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