Is Pick-to-Light More Than A Stepping Stone?

Pick-to-Light directs manual picking by lighting up bins. The Lean literature is mute about it, it’s not in the Industry 4.0 technology stack, and Wikipedia doesn’t have an article about it. Pick-to-Light system suppliers are touting it as part of both Lean and Industry 4.0 but no one else is chiming in. In the field, however, you find it in many factories, where it reduces training time and picking errors, while increasing picker productivity.

Pick-to-Light fits best in usability engineering. It’s neither jidoka nor automation because it just prompts the operator. And it’s not Poka-Yoke because it doesn’t physically prevent mistakes, the way flip-lids can. It looks like an intermediate technology, a stepping stone on the way to full picking automation but is it? It can also be viewed as a move towards using technology to make work easier for people instead of automating it.

With Pick-to-Light, pickers no longer need to look for the right bins, and Materials Managers can change bin locations without confusing pickers.

Because it supports manual picking rather than replace it, it is semi-automation. At a fraction of the cost of full picking automation, it has tangible benefits that make it popular in warehouses and manufacturing operations.

As a half-measure, however, it is not so popular with theoreticians: it relies too much on Information Technology (IT) for some and doesn’t go far enough for others. For example, that it makes errors unlikely but does not physically prevent them disqualifies it as a  Poka-Yoke device.

​Pick-to-Light technology

Lighting up bins is the easy part. Validating picks in terms of items and quantities, turning off the light once the pick is done, and reporting the pick to Production Control is more challenging.

Pick-to-Light with manual confirmation

Some Pick-to-Light systems post the pick quantity on the bin and provide a button for the operator to press once finished, as in the following picture:

Pick-to-Light with automatic confirmation

Others place a light curtain in front of each bin. Then the pickers break this curtain as they reach in and restore it when they pull their hands out, telling the system that they are done with the bin. This approach, however, still does not control the pick quantities.

The light-curtain approach requires additional hardware at each bin that is only used when the bin is lit for picking or when the picker makes a mistake. If the picker wears this hardware instead, then you don’t need to replicate it at each bin.

Pick-to-Light with confirmation by wearable technology

In picking, the state of the art is a bracelet worn by the picker interacting with a Radio-Frequency ID (RFID) tag attached to the bin. In the following picture, the picker also wears a smartphone-like device on the other arm displaying the pick quantity.

Applications

While  historians of technology have yet to research and write the story of Pick-to-Light, it is clear that successful applications  took decades to emerge, through the convergence of technology improvements and engineering creativity. 1973 was the age of mainframe computers; by the 1990s, shop floor devices could be connected through wired network; today, they can be on the IoT.

The Saridis Patent

Back in 1973, Harry Saridis, of Berkeley, CA, reveived a U.S. patent was granted to  for a semi-automated retail store. In this store, customers would fill out order forms and feed them to a computer, which would light up bins for an attendant to pick from. A conveyor belt then delivered the filled order to the customer at the check stand.

While Pick-to-Light was a valuable invention, Saridis’s application didn’t catch on. He thought stores would use it to reduce shoplifting. In operations, however, it would have been a step backwards from the supermarket to earlier forms of retail in which customers did not have direct access to the goods. Saridis’s patent shows his concept as follows:

In converting to supermarkets, retailers bet that they could trust customers, who would enjoy picking their own fruits and vegetables and would supplement their shopping lists with impulse buys. And the stores saved picking labor at the same time. It was a win/win, and Saridis’s concept was an expensive way to undo it.

From Catalog Distribution To Manufacturing

U.S. catalog distributor JCPenney reported using Pick-to-Light for consumer orders in 1999. In Manufacturing, by 2001, Dell’s plant in Austin, TX, was using it for kitting desktop computers, based on configurations recorded on RFID tags attached to totes. By 2002, Omron, in Kyoto, Japan, was using Pick-to-Light as part of its experimental Digital Yatai, to build one-of-a-kind sensing systems.

As of 2019, even though the Industry 4.0 technology stack does not include Pick-to-Light, Industry 4.0 leaders use it massively.  During Christoph Roser’s “van full of nerds” tour in Germany, we saw Pick-to-Light in use at Bosch, Kärcher, and ABB. In addition, we also saw a demonstration of an advanced system from startup ThingOS in the ARENA 2036 incubator. Previously, I had seen such systems in action at places like Porsche in Leipzig in 2014 and Dell in Austin in 2002.

Manufacturers use Pick-to-Light primarily used for kitting in supermarkets and for lineside picking at assembly stations. On factory shop floors, “supermarkets” are small stores collocated with Assembly and owned by Production. The Materials organization replenishes teh racks from the outside. Special production operators, often called “water spiders” pick kits from the supermarket and deliver parts for immediate use on the line.

Supermarket Kitting by Water Spiders

In mixed-flow assembly, the water spiders pick kits, and assembly organizations have found Pick-to-Light to be a great help in picking accurately and promptly. This is an example from the Porsche Leipzig plant in 2010:

Pick-to-Light at Assembly Stations

To bypass the kitting step, you can apply Pick-to-Light is sometimes directly on lineside shelves for operators to pick and assemble. Lineside Pick-to-Light, however, has the following issues:

1. In an assembly line, the stations must face shelves containing the items used in all the products. This potentially leads to a mismatch between product size and station size. By contrast, Omron’s digital yatai is not an assembly line but a single station to assemble one-of-a-kind systems from start to finish. They dimensioned this station to fit the product but let it move back and forth between the shelves.

2. This requires one Pick-to-Light system for each station. And it requires multiple Pick-to-Light bins for each item used at multiple stations.

The Business of Pick-to-Light

The industry’s sales forecast is for $250M in 2019, with growth at 6%/year. With a price per lighted bin between $100 and $150,  between 1.67 and 2.5 million bins will be installed this year worldwide.

Toyota Advanced Logistics owns pick-to-light supplier Bastian Solutions, and Siemens owns Dematic. Other suppliers include Daifuku Co. Ltd., Kardex Group, Matthews International Corp., and SSI Schaefer Group.

For more suppliers, see Angela Stringfellow’s list of Pick-to-light suppliers for warehouse operations from July 10, 2019. She lists the “top 50 suppliers,” which implies that there are more.

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