A warehouse management system (WMS) isn't the only software application running today's warehouses and distribution centers.

In complex distribution environments where automated materials handling systems work hand-in-hand with traditional manual systems, robust warehouse control systems (WCS) are emerging to manage and synchronize the automated putaway and picking activities.

'The WCS plays a critical role in today's automated DC, warehouse or production operation,' says Ken Ruehrdanz, business solutions manager, Siemens Dematic Corp. (616-913-6200, www.siemens-dematic.us). 'There is a huge area of control functionality that is required outside of the WMS.'

Think of the WCS as a mid-level control system for automated equipment and systems. This execution software sits between a WMS, or manufacturing execution system (MES) in a factory, and the machine-level controls of automated equipment such as storage systems, guided vehicles, conveyors, palletizers and stretch-wrap systems, executing orders received from the WMS.

'A WCS serves three functions today,' says Mike Kotecki, senior vice president, HK Systems (800-457-9783, www.hksystems.com). 'It provides a real-time interface to the rest of the enterprise system of a company; it optimizes the machines for order processing and exceptions handling and reports on those activities; and it controls inventory in automated storage systems.'

The market has driven the demand for WCS systems. 'As distribution requirements become more complex, people are looking for more visibility into their operations,' explains Sal Spada, director of research for ARC Advisory Group (781-471-1000, www.arcweb.com).

Users are not only looking for systems that can better direct automated systems. They are also looking for information-rich solutions that will allow them to periodically reassess their systems in order to adapt to the current business environment. 'The mechanism to do that is to have more information from the system that controls your equipment,' Spada explains.

This is software that can dynamically measure and report on how well a system is performing, how often it's breaking down, and how it's being maintained, Spada explains. ARC refers to this as overall equipment effectiveness, or OEE. A WCS fits that bill.

Of course, there has always been a need for some kind of software system to control automated equipment. But there are important differences between yesterday's and today's WCS systems.

For one, earlier systems were proprietary. Hence, a warehouse with equipment from a variety of vendors may have had a custom-written, proprietary software system for each machine.

'In the past, you were buying a conveyor system or a storage system,' explains Tom Wolff, business development manager, Rockwell Automation (414-382-2000, www.rockwell.com). 'Today, a WCS is written in an open computer language shared by all the devices and machines. That provides an integrated materials handling system.'

Those systems were also likely to have their own proprietary databases. Records were typically updated in batch mode. That meant that management might receive reports a day, a week or even a month after something happened, or, more likely, something did not happen.

'In today's highly-integrated systems, you are no longer duplicating databases,' says David Habib, vice president, product consulting, Swisslog (800-783-9840, www.swisslog.com). 'You now have one central database for all of the inventory and all of the automated equipment. We're sharing that with the WMS. All the systems see the same information in real time.'

That means that managers have the opportunity to respond as conditions change without waiting for a report.

'A WCS can make real-time decisions based on floor-level activity in the warehouse,' says Tim Justice, chief operating officer of IoSystems, Inc., an FKI Logistex company (859-371-6700, www.iosystems.cc). 'If a piece of equipment goes down, for instance, the system can make rerouting decisions on the fly.'

Although it performs similar functions, a WCS is not a WMS. In an automated facility, the WMS still performs execution activities for manual putaway and picking operations. It has the global view of the facility and delegates the details for automated equipment and systems to the WCS.

So, while a WMS may know that specific SKUs are stored in an automated storage and retrieval system (AS/RS), the WCS knows the exact location within the AS/RS of individual items, cartons and pallets.

'A WMS has the master inventory information and organizes the warehouse,' explains Jüergen Conrad, president and CEO of viastore systems (616-285-3311, www.viastore.com). 'But it has no ability to give commands to the machine level. That's where a warehouse control system comes into play.'

For example, a WMS may determine that a pallet of ice cream should be stored in an AS/RS. The WCS, on the other hand, will determine the optimal place to store that pallet based on stock keeping unit (SKU) velocity, cube space, as well as temperature zones in the AS/RS. The WCS will also determine the best way to route the pallet to the AS/RS staging area on a conveyor network or AGV.

'The WMS takes high level direction from the ERP (enterprise resource planning) system about what orders to fill or what inventory has to be put away,' says David Kogan, vice president of business development, ASAP Automation (502-266-9999, www.asapauto.com). 'Once that information is processed with business rules from the customers, that information has to be communicated to the automation systems. A WMS isn't designed to do that, but a WCS is.'

Although most facilities will have both a WMS and WCS, today's systems are robust enough to interface directly with a host ERP system in a lights out, highly automated facility. 'The WCS may receive instructions directly from a customer host computer to pick and consolidate orders for route truck delivery,' says Ruehrdanz. 'The WCS can direct the orderpicking and provide the logic to route and sort the items to a truck loading area in the reverse stop sequence.'

Real-time visualization of the mechanical system is one of the most important advancements in WCS systems. 'With the system connecting to the PLCs (programmable logic controllers) and microprocessors running your operation, we're managing the real-time graphics with a virtual warehouse,' says Kotecki of HK Systems. 'It's a window into the machine control layer of your facility.'

In short, a WCS allows a user to monitor the entire system from one location. Alternatively, a warehouse manager on the road or at home, can log into the system and see exactly what's happening from any computer.

The next generation of WCS systems is expected to tie monitoring and maintenance together. 'Devices at the sensor level are getting smarter and more intelligent,' says Bryan Morley, vice president, software engineering, Daifuku America Corp. (614-863-1888, www.daifukuamerica.com). 'That may lead to not just sensing when a piece of equipment has broken down, but predicting when a machine needs maintenance. That's still immature and evolving, but that's the direction for WCS in the future.'

Morley sees one other important trend developing in the WCS world. That is the marriage of a WMS and WCS together. 'In the future, you're going to see the development of a new product that includes integrated WCS and WMS modules from one company,' Morley says. 'The advantage will be that the two systems are already integrated for those users who need both modules. That will be an area of cost reduction.'

And when you marry the two together, Morley adds, 'it's hard to see where the WMS begins and the WCS ends.'

Click on the icon to learn more about warehouse controls. (The emerging world of real-time control - October 2003)