In control

Here are some tips on selecting the best controls for your materials handling operations.

By Bob Trebilcock, Editor at Large -- Modern Materials Handling, 11/1/2004

Controls and control systems have become increasingly important to automated materials handling systems.

That's because the job of moving product from point A to point B is more and more complex. Systems are managing more stock keeping units (SKUs), more value-added services, and more activity reporting than ever before. All of that is taking place in higher volumes, at greater speeds, and increasingly in an integrated fashion.

'Ten years ago, you could think of a materials handling system in terms of its components, like an AS/RS [automated storage and retrieval system], a conveyor or a sortation system,' says Paul Faber, principal with Tompkins Associates (919-876-3667, www.tompkinsinc.com). 'Today, it's really an entire business process that moves materials in and out of the facility.'

You would think then that users would put as much thought and consideration into specifying a controls system as goes into selecting a systems integrator and designing the materials handling solution.

Yet most companies take a hands-off approach to selecting controls. 'More often than not, our customers look to us as systems integrators to make the appropriate recommendation for the software and controls to fit the needs of the application,' says Ken Ruehrdanz of Siemens Logistics & Assembly Systems (877-725-7500, www.siemens-dematic.us).

There is some logic there. After all, systems integrators and original equipment manufacturers (OEMs) are experts in their field. But the wrong controls can make or break the efficiency of an operation. That's why there are important questions every user should ask about their new controls.

Ask a system integrator to name the most common problem with controls and you'll get an answer like this: 'We gave them exactly what they requested, but what they requested wasn't what they needed,' says Larry Kaiser, director of controls modernizations for HK Systems (800-457-9783, www.hksystems.com). 'The best way to avoid that problem is to address the issue up front.'

Kaiser says the first question that should be asked in any implementation isn't whether a user prefers programmable logic controllers (PLCs), PCs or some other type of control. Rather, the right question is: What is the user trying to achieve?

'Selecting a control system is a lot like buying a car,' says Kaiser, who often works with end users who are upgrading the outdated controls on their existing system. 'There are a lot of different cars on the market and they all provide transportation. What's important is how you intend to use the car.'

Depending on the facility, some users will be looking for speed and throughput from their system. Others require a high degree of real-time information. For still others, reliability and uptime are paramount. Each of those different requirements may result in a different approach to controls.

'A lot of our customers don't understand their business processes well enough to determine whether our control software system is better suited to their needs than our competitors' software,' adds Tom Wright, senior software engineer, Forte Industries (513-398-2800, www.forte-industries.com). 'But until they understand their business processes and how they intend to use the control system, they aren't going to be intelligent shoppers.'

While many companies choose controls after they have designed their materials handling solution, selecting the controls and control software is often the best place to start the process of designing a solution.

'You really should design your control system at the same time as you are redefining your business processes,' says Faber. 'Especially if you need to integrate with other equipment or a WMS [warehouse management system].'

The type of controls you ultimately choose, and the degree of integration required, may end up dictating the type of equipment that provides the best solution, Faber adds.

In the past, materials handling systems were often 'islands of automation.' Conveyors, palletizers, and automated storage or sortation systems each had their own independent control systems.

That was fine when information from the shop or warehouse floor was batched to corporate offices at the end of the day or week. But that doesn't work in an increasingly real-time world, where information feeds planning and customer service systems.

For that reason, one of the first questions Rockwell Automation asks is whether a piece of equipment is networked or un-networked. 'You really need to ask whether you're buying an AGV [automatic guided vehicle] or an AGV system that integrates with something else,' says Tom Wolff, business development manager, (414-382-2000, www.rockwell.com).

Even today, Wolff adds, it's not uncommon to hear that the user just needs the machinery to perform a specific task. 'But does that mean it will never be part of a network?' Wolff asks. 'If your requirements change, you might not be able to adapt if you don't put in the infrastructure to handle future requirements.'

Often, companies try to use the new control system to plug functionality gaps in their existing processes. Before doing that, it's best to question whether that function should be handled by a control system or another system, like a WMS.

'We recently had a customer ask us to program their control system to assign cartons to specific shipping lanes when they arrived at the shipping area,' says Wright of Forte Industries. 'What's more, they wanted the ability to dynamically determine which lanes were assigned to which shippers. When we dug under the covers we found out that their old WMS had a functionality gap they were trying to fill. They thought it would be cheaper to program that functionality into a new control system than to upgrade or replace their old WMS.'

With enough time and money, Wright says, that type of intelligence could be built into the control system. But long term, he adds, 'a WMS is better suited to grouping orders together and making those kinds of intelligent decisions.'

For years, systems integrators and control makers alike created custom, proprietary solutions. When a user's needs inevitably changed, the systems integrator sent in a team of programmers to rewrite the software.

While some would argue that control systems are still highly customized and proprietary, the industry is moving more toward open systems using common programming languages.

'System controls should support open standards and open bus architectures such as ProfiBus and ProfiNet in an industrial Ethernet environment,' says Ruehrdanz of Siemens. 'And the optimal configuration should include a single network solution from the device to a PLC to a host computer.'

The benefits of open systems include easy integration with other devices, like sensors, scanners and scales; faster communications speed on an I/O network; and easier integration with emerging technologies like RFID.

A good control system should not only handle today's requirements and capacity, it should be flexible enough to grow and change with a business. 'Your control system has to accommodate expansion,' says Faber of Tompkins Associates. 'A good system should handle that expansion without disrupting the operation process, and without changing out servers or control elements. Those are both important questions to ask.'

For example, Faber says, 'when we do our architecture, we often have a central server that's large enough to handle more than the data and information needed now. If you add another area to the system, you can tie it in with another PC or PLC so it's not so disruptive and it's flexible.'

There are two costs to a control system, says Norbert Froehlich, software development manager for viastore systems (616-656-8876, www.viastore.com).

The first is the initial cost of purchasing and implementing the controls. The second is the cost of maintaining and supporting that system in the future.

'Don't assume that because you are the owner of the system that it will run flawlessly forever,' says Froehlich. 'If you take responsibility for that system, you'll need a staff to maintain your equipment and you'll have the expense of maintaining a spare parts inventory. If you decide to outsource maintenance to the manufacturer, you have the cost and risk of getting service when you need it.'

Often, the deciding factor comes down to whether you are already using a particular brand of PLC in other areas of your operation and already have a maintenance staff trained to service that type of control system.

For some time, there has been a debate over the use PCs or PLCs to control systems. In some instances, the debate took on a religious fervor, with converts to both sides.

In truth, any complex materials handling system is probably going to be a mix of both technologies depending on the application, says Gary Cash, vice president, product management and marketing, FKI Logistex (877-935-4564, www.fkilogistex.com).

'PLCs are proven, robust and repeatable,' says Cash. 'Maintenance staffs are comfortable with them because they have been using them for years. And you know that you can get spare parts for them.'

PCs, on the other hand, are better suited at handling vast amounts of data and split-second decision-making that are common in a complex piece-picking environment. 'Complexity and speed drive you toward a PC,' says Cash.

As a rule of thumb, palletizers and conveyors are often controlled by PLCs, while AS/RS and high-speed sortation devices might be controlled by PCs.

The mix of controls may ultimately influence the choice of vendor and systems integrator. 'We have customers who prefer PC controls and customers who only want PLCs,' Cash says. 'They will select an equipment manufacturer based on the control technology they offer with their systems.'

Click on the icon to learn more about materials handling control systems.
(WCS takes control - June 2004)