Order picking basics
March 08, 2011 - MMH Editorial
From the archives: This article originally appeared in the October 2008 issue of Modern Materials Handling
You’ve heard the old saying: Those dishes aren’t going to wash themselves. Distribution is much the same: When it comes to filling orders and getting your product out the door, those Frosted Flakes, Wrangler jeans or Barbie dolls in your warehouse aren’t going to move themselves. Someone has to pick them.
“Picking is the means by which you fulfill your customer demand,” says Bryan Jensen, vice president of the St. Onge company (717-840-8181). “The more efficiently and rapidly it’s done, the more satisfied your customers will be.” Done right, Jensen adds, successful picking results in the kind of satisfied customers that drives business.
The most basic type of picking is manual picking, also known as man-to-part picking, where the picker travels to the item. There are several methods to accomplish man-to-part picking as well as several technologies that enable the different processes.
When designing a warehouse, how the product is laid out is important. Since pickers spend most of their time walking to each item on their pick list, cutting down on cycle time, or the amount of time it takes from start to finish, can greatly improve efficiency and productivity.
“In picking, it’s all about minimizing the amount of wasted time between picks,” says Lou Cerny, vice president of Sedlak (216-206-4700). “It’s not unusual for a picker to spend 70% of the time walking and 30% of the time picking.”
No matter what system a warehouse uses, some universal considerations apply.
• Fast-moving products, which spend the least amount of time in the warehouse, should be located closest to the shipping area for easy picking. That cuts down on travel time.
• Products that usually sell together should be grouped close to each other, minimizing the distance the picker has to walk to pick up all the related pieces for an order, such as sheets and pillowcases.
• When picking, make sure heavy items stay at the bottom of the carton or carriage and are picked first, and the lighter, crushable items are kept on top and picked last. “These sound logical,” says Don Derewecki, president of Gross & Associates|TranSystems (732-636-2666). “But you wouldn’t believe how many people screw it up.”
Discrete order picking involves picking all the items for an order, one order at a time. The picker goes to each section and picks each individual item for that order before going back and starting on a new order. Most often, this involves broken case picking, where the order picker is selecting individual items from a case and packing them to a tote or shipping carton that may then be palletized.
Discrete order picking is best for a small organization with low order counts. A company such as Procter and Gamble might use this method when picking a mixed pallet for a supermarket. “When you’re finished you have a full pallet,” says Jensen.
While discrete order picking is best to minimize confusion, since the picker isn’t juggling many orders, it does maximize cycle time. The picker is forced to walk the entire route for each order, cutting down on productivity.
For warehouses with more orders, especially orders with many of the same items, batch picking cuts down on cycle time, improving the picker’s efficiency. In one trip, the picker grabs many of the same items for multiple orders, separating them into different totes or cartons as he goes. Instead of traveling the same route 10 times for 10 orders, the picker can make one trip for 10 orders.
“Batch picking is best when you have a significant pick distance and multiple orders that are easiest carried en masse,” says Jensen.
The batch can also be separated into zones. In zone picking, multiple pickers are each assigned a different area of the warehouse to pick from. At the end, they meet up and exchange what they picked, creating complete orders. This works especially well when there is one item that appears in multiple orders. For example, a popular toy like Tickle Me Elmo is something a large number of people bought in separate orders, says Jensen.
Keeping the orders separate is the key to successful zone picking. “If you don’t do that, you end up having to sort them out at the end of the picking process, which can create bottlenecks in the operation,” says Derewecki.
When there is a hot item, however, too many pickers may walk through the same area, creating congestion and confusion. In those cases it may be best to go to a pick-and-pass system. In this system, pickers are assigned an area or zone and drag a cart with them through that area, picking for an order. When they finish that order, they leave the cart at the end of an aisle and the picker for the next zone begins adding to the order from their aisle. Pickers gain a greater familiarity with the zone or aisle they’re assigned to, improving productivity. There are two flavors of pick and pass: hard zone and soft zone.
In a hard zone, pickers are assigned to specific aisles and never leave them. This is the best way for pickers to become most familiar with the area. Management can also more closely monitor worker performance and productivity, seeing who needs help. But if one aisle has significantly more items than another, one picker may go underutilized, waiting for the other to finish.
In soft zone, the picker in one aisle will pick until he meets up with the picker in the next, improving productivity. In this zone, no picker is waiting in an aisle for another to finish. Soft picking, however, blurs the line between picker zones, so measuring productivity is more difficult without a labor management system to monitor performance.
“All of the basic picking concepts have been around for awhile,” says Jensen. “What’s changed is the means, with most change coming from software.” At its lowest level, picking involves a paper list with locations and item numbers. “It’s been around forever and probably will always be around,” says Cerny. But for large, complicated orders, paper-based picking is inefficient and often inaccurate.
Bar code scanning
For companies with larger orders, bar code scanning, or RF-directed picking, is the next step. Scanning a bar code label on the shelf where the item is stored verifies the picker has the correct item. Some scanners may have a handheld computer attached to them that directs the picker to the new area. Having a computer and scanner automatically reduces inventory in real time, eliminating cycle counting, says Kevin Prouty, senior director for manufacturing solutions at Motorola (866-416-8545, http://www.motorola.com). Wearable scanners, worn on the wrist, are the “ultimate way to do picking,” Prouty adds.
Keeping close track of warehouse activity requires a warehouse management system (WMS). “A WMS is basically a software solution that controls all of the inventory and all of the movements of inventory, as well as the people and equipment within a warehouse or DC,” says Steve Simmerman, vice president of Next View Software (602-524-7662, http://www.nextviewsoftware.com/).
A WMS supports manual operations, including the individuals picking, lifting and scanning items. While some facilities still operate without a WMS, that number is dropping.
“The reduction in errors is just tremendous,” says Simmerman, with software improving picking, shipping accuracy and cycle time. With a WMS, more work can be done with fewer people in the facility.
Growing in popularity, voice technology frees the picker’s hands and eyes. Voice commands direct the picker to the next location; once there, the picker verifies the location by reading a check digit and verifies the pick by telling the device when an item has been selected.
Voice devices are available in multiple languages and are more sophisticated than a telephone or car system, with a high accuracy rate of speech recognition. The picker is able to carry on a conversation with the system, even in noisy warehouse environments.
Using voice, the most natural form of human communication, gives users a combined payback of productivity and accuracy, according to Larry Sweeney, founder of Vocollect (412-829-8145). After switching to voice, some companies boast a 20% increase in productivity and far fewer errors, about only one in 10,000, Sweeney adds.
Other benefits to this technology are a reduction in training time for pickers and an increase in safety, says Sweeney. Because the picker isn’t looking down at a piece of paper or device, his head is always up and he’s more aware of the surroundings.