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By Bob Trebilcock, Editor at Large -- Modern Materials Handling, 7/1/2002

Three layers of control

To understand how these systems would work, imagine a warehouse or factory managed by three layers of control.

At the top, with the link back to the enterprise information systems, is a WMS. It receives orders that have to be filled from an order management system, and keeps an overall view of orders, inventory and labor in the facility.

While a WMS controls inventory in manual storage areas as it directs pickers and lift truck drivers, the management of materials handling equipment is left to the next layer of software, the materials handling control system (MHCS). It acts as a bridge, receiving orders from the WMS and passing on picking and routing instructions to the automated storage and handling equipment.

'The WMS knows that the inventory for the orders about to be picked is in the carousel zone or the AS/RS,' says John Ormsby, CIO of FKI Logistex (877- 935-4564, www.fkilogistex.com). 'The MHCS, on the other hand, knows the row, bin, and stock location of the inventory, and it knows what conveyor or AGV is needed to route the order to the shipping dock.'

WMS and materials handling control systems have been around for years. What's new is the level of integration developing between these two systems.

'Warehouse management and warehouse control systems used to be designed independently of one another and connected as an afterthought,' explains Kotecki. 'Now, we're trying to dovetail those two worlds.'

Rather than toss orders over a fence from one system to another, the MHCS would share information in real time with the WMS and even transportation management systems for tighter control and more effective planning.

The third layer of control takes place at the machine level, where PLC and PC-based controls open and close gates, spin motors and conveyor rollers, and control diverters and sorters.

Today, machine controls passively wait for instructions from the MHCS. But as systems evolve, Spada and others envision decision making being distributed down to the machine level. What will make that possible is more powerful controls enabled by onboard computing. Spada calls this distributed intelligence.

'You'll always need an intermediate layer, but I believe the MHCS will evolve into a maintenance, diagnostics and information center,' says Spada. 'Order picking, routing and sequencing decisions will all be made by individual machines.'

The connecting piece that makes distributed intelligence possible is a dynamic materials handling database shared by the WMS, the MHCS and machine-level controls.

Now, when the WMS sends an order to be filled by the AS/RS, the storage system queries the common database to determine routing of the inventory rather than wait for instructions from the MHCS.

'From the smallest element of a conveyor, there's a need to distribute intelligence right down to the actuators that turn the powered rollers on and off, and move information peer-to-peer up and down the conveyor system,' says Tom Wolff, business development manager for OEM programs at Rockwell, Automation (414-212-5200, www.rockwellautomation.com). 'That means less control is needed from a centralized perspective. You want to distribute as much flexibility as possible down to the machine level.'

Take, for example, a shipping dock with ten palletizers. Today, the MHCS determines the workload for each machine, based on an established set of rules. But in a world of on-demand shipping, where requirements may change dynamically, those decisions could be made at the machine level through onboard intelligence that reacts to real-time conditions on the dock. Equipment can be dynamically coordinated to route and reroute around congested stations and improve the flow of materials.

Bringing power to the PLC would also enable real-time event management and alerts on the warehouse floor. 'A PLC can be programmed so that when it sees a certain package, or when a bottleneck occurs, it notifies someone who has subscribed for that information to address the problem,' says Robb Dussault, product marketing manager, Square D/Schneider Electric (888-778-2733, www.schneiderelectric.com).

Hurdles to clear

Much of the technology for an information-driven materials handling system is available now. Still, Spada believes that widespread adoption of these systems is two or three years off.

The cost of implementation is one hurdle. 'Right now, this is for the customer who understands the importance of extreme up time, like suppliers in just-in-time environments that require a predictable response,' says Ken Ruehrdanz, manager of marketing, Siemens Dematic (877-725-7500, www.rapistan.com). 'Those people will justify the ROI on their business model.'

But price is only one hurdle. A lack of industry standards is another. With literally dozens of materials handling suppliers offering custom-designed systems, there are no standards of communications between devices or standard interfaces to WMS systems.

Industry efforts to develop common solutions are underway, however. Late this spring, there were initial discussions about the importance of such potential solutions at a meeting of Material Handling Industry of America (MHIA), the industry trade organization. Individual companies are also working to develop a standard interface for their equipment and an MHCS.

'We're doing this first with our own products and later we'll stretch that out,' says Ormsby of FKI Logistex. 'We'll have standard, pre-defined intelligent XML interfaces for how you talk to different pieces of equipment. That way if another manufacturer comes along, as long as they can define their equipment in XML, we will be able to add it to the system without reprogramming the software.'

But, common solutions will be slow to develop. 'There are so many vendors out there, that getting everyone to agree will be a challenge,' says Bradford Beale, general manager, industrial applications division, of Comtrol Corp. (800-926-6876, www.comtrol.com), who is involved with the MHIA effort.

For that reason, many vendors expect handling control systems to continue to manage the work of the machines for some time to come; distributed intelligence will take longer to proliferate.

In the end, customers may be the determining factor on how quickly these initiatives bear fruit. 'End users are demanding that the automation and machine vendors comply with standards,' says Dussault. 'Some OEMs have been quicker than others to try to comply, but ultimately, the customer will win that battle every time.'