USB Flexes Its Industrial Strength

April 23, 2009
PCs have long since taken over the factory floor as automation and control platforms. Why shouldn't USB connectivity follow?

As PCs proliferate, their technologies become more affordable for a growing range of industrial applications. Programmable automation controllers, for example, are basically ruggedized PCs. Meanwhile, Ethernet has transformed from an office/home network to an industrial network that’s rapidly becoming the norm in factories.

USB is also extending its industrial presence. Data-acquisition systems use it for easy connections and expansion. Robots employ USB for training and setup. More sensors are now being connected with the ubiquitous interface as well.

This industrial expansion comes atop phenomenal growth. In little more than a decade, USB has become as mainstream as any consumer electronics standard. Over 2.5 billion USB devices shipped last year, and there are more than 6 million installed USB products, according to Jeff Ravencraft, chairman of the USB Implementers Forum.

Industrial designers are adopting USB for the same reasons it’s popular in consumer markets. The standard’s plug-and-play capabilities are as foolproof as any computer interface, and its bandwidth is sufficient for a huge range of applications.

“When you look at all the buses, it’s one of the easiest to implement. And USB 2.0 has more bandwidth than many of the Ethernet networks installed today,” says Brett Burger, National Instruments’ data acquisition product manager.

USB’s 480 Mbits/s is about half the speed of Gigabit Ethernet, which is gaining acceptance even though it’s still a smaller portion of the installed base in industrial, says Burger. However, versatility is far more important than speed in many industrial applications. USB gives industrial designers the freedom to add components or systems, locating them remotely from the controller.

“You can put the data-acquisition hardware up to five meters from the host,” says Mark Bohm, a system architect for SMSC. “If you need an LCD panel with an HMI (human machine interface), you can put it wherever it’s best for the operator.”

DIVERSE APPLICATIONS USB’s reach continues to grow. New applications and new products are spiraling upward together, helping extend the architecture’s role in the industrial world.

In data acquisition, USB provides an easy way to add and swap out modules as needs change. NI now has nearly 50 modules, giving engineers a number of measurement options as they build test racks (Fig. 1). These modules span NI’s CompactDAQ, Compact Field Point, CompactRIO, and Compact Flash lines, with some other chassis also providing USB connectivity.

Other instrumentation companies are also broadening their lines. More of them are taking advantage of the display and control functions in a controller to make the USB modules as compact and efficient as possible.

“Our latest DMMs (digital multimeters) and switching modules have no buttons or displays, so they have a very small form factor,” says Tee Sheffer, CEO of Signametrics Corp. “Their power consumption and heat generation are also much lower.”

Signametrics’ DMM consumes only 2 W, well below the 30 W needed for competing devices that include displays and control buttons (Fig. 2). At that level, the device can be powered over the USB wiring, eliminating the need for a power cable.

Sensors are another technology that’s constantly changing as factories evolve. Versatile connectivity helps technicians install sensors quickly when lines change or when managers want another type of measurement.

“USB is being used for a lot of general-purpose I/O like proximity sensors,” says Dan Harmon, product manager at Texas Instruments. “It works very well for products with relatively low bandwidth that are fairly close to the controller.”

In other fields, USB’s presence affords end users more freedom. In robots, the connection helps operators meet the continuing changes that come with lean manufacturing and flexible manufacturing (Fig. 3).

“Our latest robot controllers support USB interface both on the door of the controller and on the teach pendant,” says Claude Dinsmoor, general manager of product development at FANUC Robotics America Inc. “Both offer the convenience of being able to load and save robot application data and programs to any common memory device/ stick.”

The popular link provides additional benefits. “USB on the robot provides easy-to-use local backup of application files in cases where the robot is not connected to a factory network via Ethernet,” says Dinsmoor.

EASY EXPANSION As in consumer products, USB is attractive because it greatly simplifies the addition of peripherals to a system. That’s very important in continously evolving industrial environments. Some of those products will become permanent parts of the design, and others will be attached only when it’s time to troubleshoot. In either instance, simplicity is a critical element.

“Once you have the USB port, you can add a hub and hang several devices off a single port without a huge software impact,” says Bohm. He notes that a few operating systems, though, don’t support the hub concept, so engineers need to explore that before using that solution.

However, products lacking full support are fading away rapidly. In many areas, the ability to add more connectivity is a central aspect of most designs. Consulting houses that work with a range of customers say multiport capabilities are now common.

“Two of the five USB-enabled designs we’re doing now have eight high-speed 2.0 USB host ports. Future designs will have up to 12 high-speed 2.0 host ports,” says Paul Nickelsberg, president of Orchid Technologies Engineering and Consulting.

But even in new designs, adding a number of ports isn’t always an option. In compact designs, there isn’t room for all of the connectivity that’s needed in products designed for use in a number of diverse industrial environments.

One alternative is StackableUSB, an enhanced version that increases I/O capabilities while adding ruggedization. It gives designers the benefit of USB’s broad availability and the ruggedization of PC/104, providing multiple channels of USB through a single connector. It supports up to 10 data channels and seven hubs on each USB channel.

Micro/Sys, which headed the creation of the specification, has unveiled more than a score of boards that let engineers link USB devices to a range of different CPUs. Samtec offers ruggedized connectors that tie stacked I/O boards together. Engineers can stack several boards together to add I/O while only creating a bit more height.

Though many systems being developed today include numerous ports, having just one or two connections isn’t a huge limitation. Several hubs can be linked together to add more ports. Latency may have to be accounted for when additional cables and hubs are incorporated, but that can be far more effective than replacing an installed product or redesigning one with limited I/O. Daisy-chaining often provides a large increase in connectivity.

“With a hub, you can cascade up to five levels, so you can add several ports to a chip that only has a single USB port,” says Steve Roux, senior strategic business development manager for NEC’s Digital Consumer & Connectivity Unit.

That sort of connectivity is most likely to occur in older systems. “Older systems” is a large category in industrial applications, where there’s often reluctance to replace any equipment that’s running without problems. A few of these products are so old that they’re still running DOS and using floppy disks. Replacing floppies with USB data storage can breathe new life into DOS-based applications.

“The most unique of our clients use USB in products that still run under MSDOS or DR-DOS environments. As floppy disk drives become obsolete, DOS-based products turn to USB for file system data storage,” Nickelsberg says.

Switching from a floppy to a USB thumb drive will significantly boost performance as well as convenience. But for many industrial applications, performance isn’t a major issue. The first version of USB, 1.1, will often suffice with its 12-Mbit/s data rate. Simplicity, ease of connectivity, and reliability are more important than bandwidth.

“USB 1.1 speeds are sufficient for most applications since the typical robot application does not require large file sizes, normally less than 1 to 2 Mbytes total,” says Dinsmoor.

Though USB 2.0 was finalized early in this decade and has become the de facto version in the broad market, chips compliant with the original version are still being sold. “USB 1.1 is still used for mice and keyboards,” says Bode. (For more on the latest version of USB, see “The USB 3.0 Speed Bump.” )

One drawback for industrial users is that many of the chips and other products are designed only to consumer requirements. That’s a problem in industrial facilities where broader temperature ranges are required. The availability of ruggedized products is expected to rise now that many automakers are integrating USB into vehicles to provide connectivity for MP3 players and other consumer products.

“There are a number of high-temperature solutions, and there will probably be more coming as the auto industry increases its use of USB,” says Mark Bode, vice president of connectivity marketing at SMSC.

MANY DRIVERS When adding new modules, driver support becomes an issue. However, this usually isn’t the case with USB, which has broad support from most popular operating systems.

“Once you buy silicon, there’s no additional driver development. That’s a tremendous value added for designers,” says Bohm. “In lab environments, there’s been a lot of x86 and Linux development so there’s a huge support structure that comes with USB.”

However, that support structure doesn’t span the entirety of the diverse industrial field. Though USB drivers are often seen as ubiquitous, areas still exist in which unusual or custom products aren’t plugand- play compatible. Drivers are one of those areas.

“There are a number of classes of drivers, and the complexity behind them is growing,” says Tony Zarola, DSP product line manager at Analog Devices Inc. “USB is so common, people make assumptions that aren’t always true. It’s not easy to implement if you don’t have the right drivers.”

The availability of drivers varies for different chips and operating systems. Parts with smaller industry usage are less likely to have broad support. That’s more important in industrial applications, where many drivers for unusual products may not readily appear in libraries.

Zarola notes that when process control data must be time-stamped, drivers that support this mode may not be widely available, forcing equipment designers to write their own or search for partners. Most chipmakers have partnerships that extend beyond the mainstream to include many of these unusual drivers, he adds.

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