Task Interleaving: Optimising Warehouse Workloads

Task Interleaving: Optimising Warehouse Workloads

Applying the concepts of resource management and task control and referring to a logistics strategy where two or more tasks are combined into a single run through the facility.

Many warehouse operations have evolved so that separate teams are dedicated to specific tasks. For example, one team manages goods inwards, another looks after stock movements, and yet more cover order picking, packing, despatch, and so on. There are various reasons for this approach and many warehouse operators believe in it, perhaps for reasons of management simplicity or accountability. But look more closely and it is soon apparent that this type of structure can be inefficient. Modern warehouse management systems (WMS) have the capability to support complex task allocation and management that makes much better use of resources, equipment, and infrastructure. This is generally known as task interleaving.

In the organisational structure outlined above each member or a team is typically assigned a task to handle an item from one location to another. As soon as they have completed the task, they return to the starting point to receive a new task. Lift truck operations are a good example. The operative collects a pallet from the loading bay and handles it to a racking location. They then return to the loading bay to start a new task. In this scenario the operator and lift truck are operating at barely 50% capacity because they are doing no productive work on the return leg of the task.

Lift truck operators may be operating at barely 50% capacity because they are doing no productive work on the return leg of the task.

The basic concept of task interleaving is to transform this wasted time and movement into something useful.

So instead of travelling back to the loading bay empty, the operator and lift truck could be giv en a task that starts close to their current location. This might be to transfer some stock in the warehouse, replenish an empty picking location, or handle stock from storage to the loading bay, and so on. In an ideal warehouse environment, there would be no wasted truck movements because each task would start at the point the previous one ended in a continuous and unbroken chain of 100% useful and productive working.

In our theoretical warehouse that would represent a 100% uplift in productivity for the lift truck and operator (from 50% to 100% productive time) but what would be the uplift in a real-world setting? In reality it is rarely if ever possible to get up to 100% utilisation no matter how well organised the operations. But what impact would it be to a business that could achieve just a 25% efficiency improvement? That is a significant amount that could easily be measured to justify any cost or investment involved.

What impact would it be to a business that could achieve just a 25% efficiency improvement?

WMS versus manual task management

Like many things in the warehouse, it is entirely possible to manage all tasks manually. But in reality, the complexity of modern warehouse operations means that a WMS can offer a more efficient solution. In fact, many warehouses currently manage the tasks outlined in our basic scenario using a WMS. And many already use them – often within the same functional areas – to reduce the number of wasted or empty movements. This is clearly a good benefit but the complexity of modern warehouse operations with a much wider range of tasks to handle and pick items of many different shapes, sizes, and weights means that such systems can only go so far.

This is where task interleaving comes in. This refers to a logistics strategy where two or more tasks are combined into a single run through the facility. For example, pickers can retrieve the SKUs needed for an order and then take advantage of the return trip to replenish products. By minimizing unnecessary movements, task interleaving aims to increase warehouse productivity and reduce unproductive travel. This approach is particularly useful in facilities with manual handling equipment, where operators can optimize their trips by combining tasks.

Task interleaving, uses the concepts of resource management and task control and refers to a logistics strategy where two or more tasks are combined into a single run through the facility.

As it happens, we do this sort of thing all the time in our daily lives.

We might, for example, fill up the car with petrol on the way to or from the shopping centre. Or we will drop off the recycling on the way to collect the kids from school. Combining two or more tasks like this in the same trip is more productive: it saves precious time so that we can do something else instead and saves money which we can save or spend on something more important. The same concept applies in the warehouse with task interleaving but it is just a bit more formalised and structured.

The key for the warehouse is having the flexibility and adaptability to manage tasks and resources in real time so that everything is utilised for maximum utilisation, productivity, and efficiency. In addition to allocating tasks this way, warehouse operations need to respond dynamically to constantly evolving demands, requirements, workloads so that the maximum number of orders are fulfilled in full and on time in any given timeframe. They increasingly need to do this when juggling between the differing challenges presented by conventional handling and order picking, e-commerce, and omnichannel services.

Task interleaving requires a completely different approach to how staff, resources, areas within the warehouse, and items themselves are viewed. The complexity involved means that the only feasible solution is to use a WMS that can deliver these capabilities. From an organisational point of view, this requires the switching from siloed groups dedicated to areas of the warehouse or specific types to task to a single group of operatives who can undertake any task at any time.

WMS with these capabilities include ProWMS from Principal Logistics Technologies. This advanced application manages task interleaving using the concepts of resource management and task control. To configure the application, supervisors first define various parameters about resources and assets that perform tasks such as people, lift trucks, order picking trucks and so on. Supervisors can also assign varying attributes to resources such as shift patterns and similar.

The next step is to define zones.

These are simply user-definable areas such as warehouse A, warehouse B, mezzanine, a hazardous area, a bonded area, and so on. Using this information the WMS can link resources to the zones where they are permitted to operate. This might include, for example, restricting operatives without the proper hazchem training from working in any hazardous zones.

The final step is to associate resources with each task type

This might include, for example, ensuring that an operator without a lift truck licence cannot perform tasks that would require a lift truck. Remember, we are talking here about an environment where any operative can be allocated to any task at any time so it is important to have these sorts of definitions and restrictions in place.

The application takes care of all the processing and decision making involved to maintain a steady flow of tasks so that more operatives and infrastructure are used more effectively more of the time.

The WMS will dynamically assign pre-defined tasks in real time

Once all of these rules and parameters have been defined, the WMS will allocate tasks dynamically and in real time using the known location of each operative. The application takes care of all the processing and decision making involved to maintain a steady flow of tasks so that more operatives and infrastructure are used more effectively more of the time. This is the basis of how task interleaving offers a new way of optimising warehouse operations.