Practical Device Networks

With Intelligent Devices and Lower-Level Networks, Machine Builders Can Build and Commission Faster, and Provide More Reliable Performance

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By Loren Shaum, contributing editor

Legacy machines have many more hard-wired devices than networked devices. That’s no surprise. But today, with manufacturers demanding smaller, cheaper machines with quicker delivery and commissioning, machine builders must focus on ways to reduce build and start-up times. Less wiring is an important means to accomplish those objectives.

In a typical machine, there can be multiple levels of networking depending on machine complexity. Figure 1 represents a typical machine, showing elements invariably found on every machine in one form or another.

 

The Basic Element

Figure 1

Figure 1: A typical machine connectivity diagram. Green
arrows represent typically hardwired elements, while red arrows represent typically networked devices.

The challenge for machine builders is to figure out which elements can be networked. If the machine is spread over a large factory-floor envelope, then networking from a central or distributed control intelligence source makes sense. Distributing networkable I/O and servo drives strategically throughout a machine envelope based on functionality looks like a great design idea. The higher the device count and the larger the machine, the more reason to choose distributed, network-connected control.

What really determines a network choice? Perhaps it comes down to something as basic as serial connectivity versus parallel connectivity, i.e., connecting everything in some kind of “daisy-chain” arrangement, rather than connecting each device directly to the control intelligence. Figure 1 indicates the levels of connectivity typically required on every machine.

Simplifying Network Designs

The really time-consuming parts of any machine commissioning are wiring and programming, and their subsequent debugging. Consequently, keeping hardware platforms less complex becomes a driving force toward simplicity. Multiple hardware configurations (Figure 2) are tougher to implement and debug in a timely fashion, and still remain competitive.

With an integrated PC-based control solution (Figure 3), control and network complexity is reduced, especially when more common fieldbus drivers are onboard. With such controller configurations, machine builders and system integrators can standardize controls across multiple machine configurations, and implement local or distributed motion and/or I/O control on one compatible network.

One machine builder incorporating this strategy is DynaPath, Livonia, Mich. DynaPath has been supplying machine tools and retrofit controls since 1957. “In this competitive market, we need a control strategy that’s the simplest to integrate into any of our machines, simplest to debug, and provides all the control functions that our machines require,” stresses Paul Barnhardt, DynaPath’s sales VP. “We can interface easily to servos and devices with the controls mounted on the machine.”

Dynapath uses HA Controls’ software-based, networkable machine control built around HA’s Performance Series (P Series) machine controllers. P Series is a compact hardware platform with several touchscreen sizes and software for HMI, SCADA, PLC and motion control—plus multiple fieldbus drivers—integrated on one WinPC32 Pro platform. “Our platform offers more functions with less hardware, and for networking we can incorporate drivers for virtually any fieldbus,” claims Dr. Jacob Pien, president, HA Controls. “This allows machine builders to connect seamlessly to their fieldbus for instant networking.”

Device-Level Networking

Devices on machines sometimes incorporate intelligence for functionality and/or network connectivity. As device intelligence increases, networkability increases, too. Several suppliers now offer fully networkable smart devices. Even with the move to smarter devices, most installed device connectivity remains hardwired, some to a network interface module, while others are wired directly to the control intelligence through I/O interfacing. If wired to a network interface, connections can be made to a number of proprietary networks.

 

Complex Connectivity

Figure 2

Figure 2: A classic, complex machine architecture with intelligent sensors, motion control, HMI, and communication drivers can have significant debugging requirements. Red arrows represent possible networked devices, while green arrows represent largely hardwired devices.

“I have no hard numbers, but I’d be very surprised if the ratio of installed intelligent sensors to standard sensors is more than 0.1%,” says Helge Hornis, manager of Intelligent Systems Group at Pepperl+Fuchs. “I know of AS-Interface and DeviceNet sensors, but I’m not aware of any Profibus or Ethernet sensors. The situation is different if you include safety inputs. Lots of AS-Interface-compatible e-stops and door interlocks are deployed. That ratio might be as high as 10%, and is increasing as companies improve their solutions.” These numbers seem small given all the hype about smart wireless devices.

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