Logistics News: Task Management versus Task Interleaving in Warehouse Management Systems

Task Engine is at the Core of WMS Capabilities; Interleaving Isn’t for Everyone, but Can Drive Large Productivity Gains

logistics news taks management

SCDigest Editorial Staff Jan. 3, 2012

At the core of a Warehouse Management System’s ability to improve DC management and reduce labor costs is the WMS software’s “task management engine.”

The task engine is configured to understand all the possible types of work in a DC, especially for mobile workers. That work includes such activities as putaway, order picking, replenishment, truckloading, and much more (see graphic nearby). WMS systems will usually offer options about which types of tasks the system should assign versus which ones operators will self-assign (or receive through a supervisor) and report via scanning or other means what work they have performed.

The task management engine really can be considered the brains of the WMS, understanding what work needs to be accomplished, and assigning the work from its queue to specific workers, typically via wireless RF terminals or voice commands. In higher-end WMS systems, those tasks are assigned to individuals based on the so-called “3 Ps”:

Permission: Is the operator permitted to do a specific task (training, certification, on the right type of equipment, etc.)?

Proximity: Is it efficient for the operator to do a task based on where he or she is in the DC right now compared to others?

Priority: How important is this task (for example, is it a “hot” replenishment”)?

Each WMS will have its own specific algorithms for how these factors are combined to assign tasks to workers. Generally, the task management configuration process will offer flexibility in how these rules are established. The system should also allow the generated task assignments to be “overruled” in real-time by floor managers if needed, though the ease of doing this will also vary from system to system.

An early problem with WMS task management systems was that in a busy distribution center, low priority tasks sometimes never were sent to the floor, and they were constantly trumped by new higher priority tasks. The vendors solved this by putting a configurable timer on each task (say 10 or 20 minutes), after which the priority would be bumbed up one level (say from a 5 to a 4).

The task management engines are increasing “event driven.” So, for example, the event of a very narrow aisle truck dropping a pallet it picked up at the end of an aisle triggers a task for a traditional lift truck to come move it to staging or other location.

Task Interleaving Goes a Step Further


“Task interleaving” takes the power of the WMS task management engine to a new level by combining tasks for operators in a distribution center to increase productivity and reduce equipment “deadheading.” Interleaving isn’t for every DC, but can drive big productivity gains for those that can make it work.

While putaway, picking, etc., are the most obvious and generally most critical tasks to consider for interleaving, the maximum value will be achieved if the task engine is looking across most or all types of work in the DC in its pool of work to be assigned.

In DCs without interleaving, at any given time workers are typically focusing only on single tasks, such as putaway, which would mean driving back empty to receiving after each piece of work.

As shown in the illustrations nearby, with task interleaving different types of tasks can be assigned to a given operator, such as giving an operator a full pallet pick for a replenishment task in the case pick area after he or she has just completed a full pallet putaway.

The tasks assigned to workers are still determined based on the three P’s of permission, priority and proximity, but now with the pool of available assignments across task types, not for just a specific type of task.

For example, after a full pallet putaway, the WMS might identify that there is a storage location nearby for a replenishment task to take a pallet to the case pick area. That different task type is assigned to the putaway operator, reducing the amount of empty travel versus single threaded work assignments.

The more broad the list of possible tasks that are defined in the task management engine, the greater the pool of potential work assignments and hence the greater the opportunities to efficiently combine tasks and reduce deadheading.

That, however, can sometimes come at the price of greater operational complexity for operators, who must master multiple tasks.

As shown in the illustration below, in a traditional warehouse system, workers on mobile equipment perform specific DC tasks, and return to repeat those tasks upon completion. The result can be substantial levels of “deadheading,” or driving the fork truck or other equipment empty.

task management
With task interleaving, the WMS looks to combine different types of tasks to reduce this deadheading. As shown in the graphic below, an intelligent WMS can understand the total work pool that is available on the floor, and look for a complementary task that can be linked to the original task assigned to the operator.

task management_2
Designing a DC for Task Interleaving

Companies naturally most often just think about how to use tasking and task interleaving within the facility and DC layout that they currently have. But, in many cases, it may be worth considering the potential to maximize use of interleaving when designing for its potential in a new DC, or to evaluate layout or process changes in an existing DC to maximize productivity through interleaving.

That’s what one large food company did when it recently implemented task interleaving.

Like most companies, the DCs this company operated had all its receiving doors on one end of the building and its shipping doors on the other.

But the company wanted to link receipts from its factories with truck staging and loading to support cross docking. So, it reconfigured its doors into sets of five receiving and five loading docks each. By doing that, it was able to achieve double-digit productivity gains in these operations, since the putaway task was so close to the drop off point for loading.

There are three key points

1. If you are building a new DC, be sure to consider the potential for task interleaving in your DC design.

2. If you are considering interleaving in an existing DC, consider changes in layout or flow that might improve the benefits interleaving can deliver.

3. If you are using savings from task interleaving as part of your cost justification for a new WMS, be very sure you can really make the capabilities and process work in your operation. The change is not trivial.

Companies often find productivity gains of 10-20% when moving to interleaving, and sometimes as high as 30%.

While task interleaving was more myth than reality in terms of real DC deployments 10 years ago, today an increasing number of companies are using the approach.