Are you still sitting on the fence (www.ControlDesign.com/pcplc)? Some controls engineers say they’re moving to PC-based control, but harsh environments call for rugged components.
“PLCs are rugged, time-proven monsters of reliability,” says Max Falcone, lead engineer on vision-aided tooling for Comau (www.comauinc.com), which develops complete turnkey systems for transportation and green-energy industry sectors. “That's why maintenance people and end users love PLCs. The unfortunate part is that most of them require a fond understanding of ladder logic. The idea of a rugged PC is not an easily accepted paradigm shift because so many people have tried to put a standard desktop PC in a manufacturing environment, and it failed. While the hardware inside might have been cutting-edge at the time, the tower is not made for that environment. They suck air across the tower and in a plant where there is welding going on this become a black, greasy, sticky mess; after a while the fans stop working and the computer eventually fails. We went with the proven technology of the Nematron ePC-Plus, and all the software is written in C++.”
Rodney Price, senior electrical engineering specialist, Belvac Production Machinery (www.belvac.com), a beverage canmaker in Lynchburg, Va., sees ruggedness as a safety net for his applications. “We put our PC in A/C cabinets that are sealed from the environment,” he explains. “So technically, a quality PC of any sort, even commercial, should perform very well. But moving from the world of PLCs, which are notably rugged, we feel safe in knowing that our PC can withstand the harshest environment that a hermetically sealed, air-conditioned control panel can dish out. We are attracted to Beckhoff PCs due to their ruggedness.”
Any and all sorts of industrial applications are well-suited for industrial PCs (IPCs), says Corey McAtee, product manager at Beckhoff Automation (www.beckhoffautomation.com/ipc). “Perhaps a more constructive way to look at this is which applications are best-suited for specific processors?,” he asks. “The applications can be simple sortation systems running on a $500 IPC with a low-end processor all the way up to complex CNC systems running on a $2,000 IPC with a high-end processor. IPCs can automate machines that are involved in all forms of manufacturing and production. Small ARM-based processors running at 233 MHz up to Intel Core2 Duo at 2.16 GHz and beyond provide the perfect range to scale with great precision to unique control requirements and budgets.”
Beckhoff supports Windows XP Pro, XP Embedded, Vista and Windows CE. “The deciding factor will be which hardware and software, if any, the system designer intends to use with the system,” explains McAtee. “In the case of XP Pro or XP Embedded, one may be selected because a user has a third-party software or hardware requirement that must run in parallel with the machine control—as two quick examples, this could include CAD/CAM software or a USB vision device. If there is no third-party hardware or software requirement, I recommend Windows CE. It’s cost-effective and is leaner, compared with the other OS variants. CE also takes up less storage space on the controller, is easier for the designer to support and is easier to modify for customized functions.” It also has a large support base of users online that provide tips and tutorials for customization, he says.
“The request I get most is not to put Vista on a PC,” explains Ralph Damato, vice president—product management at Nematron (www.nematron.com). “We are moving from an OEM version of Windows XP to Windows XP for Embedded Systems. That’s a way I can continue to help our customers to deal with Windows XP. Downgrade rights is another way. Windows XP can be put on a computer with a Windows Vista Business or Ultimate packages. The biggest problem with this is the customer doesn’t receive any way to put XP on the machine again. It’s also more expensive.”
Nematron’s customers also are pushing for more enterprise connectivity. “People are comfortable with Excel,” continues Damato. “When they’re looking for process data to share on a network, they can easily connect this to anything to analyze or sort. More people are interested in doing that for just-in-time efficiencies so they aren’t building more than they need. You don’t need to pay for extra packages to convert the data.”
Belvac uses PCs for database applications, machine control and HMI, says Price. “We use a whole range of operating systems,” he explains. “It depends on what we are doing with the controller. For simple machine control, we use Windows CE. For more integral things, such as manual on machines, we use Embedded XP. And for my project, I am running a custom HMI designed in InduSoft Web Studio with a ton of VB scripting and a Microsoft SQL 2008 database. For this setup, I am running Windows XP Pro. I have a secondary PC doing some of the work that is running XP as well, but only because it was handy. It could easily run Embedded XP or, if I want to sacrifice the dual-core processor, Windows CE.”
For Falcone, the PC means freedom. “We can program in any language we feel comfortable with,” he says. “For us, PC means flexibility. When you have a PLC system, you’re tied into ladder logic. We’re writing in Visual Basic or C++. The interface—Windows XP—is common and familiar to most people. The hardware options are plentiful, and you rarely get locked into proprietary licensing. You can truly make them your own and cater to your customer's needs. Sure, you can do this with a PLC, but it’s a lot of work. The other advantage of a PC is true multitasking. This is huge for us in our RecogniSense product as we are capturing images, calculating positions and communicating to the robot all at the same time, taking advantage of the dual-core processor in the Nematron ePC-Plus.”
A huge area for advancements with multi-core processors is that you can essentially split the processor and tie each core to a major process, explains McAtee. “One core, for example, can manage CNC, one can manage I/O, and one can manage HMI,” he says. “When dedicating individual cores, system designers can truly optimize machine functionality and pile on high-end processes on one PC platform.”
The panel for Comau’s RecogniSense, a single-camera, six-degree-of-freedom recognition system used for robotic guidance, is designed around the PC to make use of its inner workings to keep the air inside the panel constantly moving, explains Falcone. “By mounting the PC higher in the panel and keeping the components that generate heat lower in the panel, we take advantage of the natural convection along with the fan in the PC to cool the panel,” he says. “This is the reason we don’t have an air conditioner in our panel, which is another failure point in their systems.”