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Distributed I/O helps realize designs

Distributed I/O helps realize designs

The advent of distributed I/O systems, such as DeviceNet, has given electronic-fabrication equipment manufacturers more freedom in configuring their products into efficient and affordable packages. These, in turn, allow their customers flexibility in getting the electronic component designs made on such equipment to market.

Equipment using distributed I/O is simplified, having many terminal block connections between devices eliminated, for instance, because the bussed devices themselves function as the blocks.

Newport Corporation's Advanced Automation Systems Group (Chandler, AZ) produces compact and versatile electronics fabrication systems such as its Solar Cell Unloader. Until recently the operation was a separate company known, fittingly, as Unique Equipment.

Vern West, director of operations for the group, says that without DeviceNet to link sensors and output devices, including robotic functions, the unloader would be bulkier, harder to integrate, and more expensive. The system keys on using the DeviceNet distributed I/O protocol components from Wago (Germantown, WI). The unloader acts like a traffic cop in solar cell production for satellites and ground-based power applications. It sets up pallets of cells for sealing with epoxy between layers of glass and then moves them into curing chambers as required.

While other manufacturers furnish DeviceNet components, West says that the Wago system "Allows a mix of I/O inputs in terms of voltages, and sinking and sourcing, without wasted space. And you only have to buy the I/O counts you need, rather than in blocks of 32 or 64." By sourcing and sinking he is referring to two possible configurations. To illustrate with a relay, sourcing would see the I/O apply power to it, as is the general practice in the U.S. Sinking, common in Asia and somewhat in Europe, would have the I/O ground the relay. Thus, notes West, Newport designers can mix both types of equipment in a product, from manufacturers around the world, "coming up with the best system to do the job."

Without distributed DeviceNet I/O, says West, running cables from each device's I/O to a terminal block and then to the field would be a wiring nightmare. With DeviceNet it's just a 4-wire bus. And he adds that "Wago's complete and broad line of components ensures completeness with one-stop shopping."

But not for all. However, West admits that distributed I/O is not always the way to go. Such is the case with prior existing systems or a controller with built-in conventional I/O. GET Systems (Albuquerque, NM) tried distributed I/O on one of its component plating systems in an R & D application but uses conventional I/O on its production machines. "They are stand alone systems, so we stick with PLC control," says Luis Armijo, engineer and customer service manager.

The radial flow. Through platers are about 84 inches square and take the place of barrel-plating production lines up to 80-ft long. Barrel plating uses baskets (or barrels) to hold parts transported from one processing tank to another. The radial plating machines contain the process within a cell that spins to force the parts onto the outer cathode and plating solutions are then introduced into the tank. All chemicals can be easily reused and recycled. The plating thickness is easy to control, notes Armijo. The machines are used to plate everything from surface mount electronic components to surgical equipment. And, he adds, the machines are easily adapted to process the parts the customer wants.

Armijo does note GET uses Wago terminal blocks and fuse holders for assembly of the machines: "With cage clamps, it's quick and easy. Just crimp the terminals onto the wire then stuff the mating bare wire in. And Wago has a better component selection available."

Fabricate your design efficiently

Distributed I/O systems have characteristics that may be used to advantage in your product design. Here, Vern West of Newport Corporation's Advanced Automation Systems Group, which makes electronics fabrication equipment, offers several considerations to keep in mind.

With ease of changing sensors or adding outputs, distributed I/O control systems allow cost-effective changing of manufacturing processes to produce updated designs. "Since adequate I/O is usually hooked up already," says West, "you just have to add wires for the additional sensors and not worry about the control."

For specialized product production, different manufacturers' equipment, on DeviceNet say, can be accommodated on the same production line. If a temperature controller, for example, from a specific manufacturer is needed and only has an RS-232 port available, it can be plugged into a node adapter for DeviceNet use. Which leads to another advantage.

DeviceNet allows for long lines, up to nearly 4,100 ft, with only 4-wire cabling. Thus shorter-range RS-232 hookups, as noted above, can effectively be given longer range. With long, simplified cable runs possible, as long production lines as are needed can be set up and centrally controlled.

West adds that in the case of Wago's I/O systems, "The cage-clamp terminal blocks are a real advantage in assembly time. Just push in the contact with the appropriate tool, stick in the wire and it's a good connection." With screw connections, he notes, "You have to screw until tight and you need an experienced technician to regulate the torque" so the connection is not too tight to break the wire or too loose to open under vibration and thermal cycling. West adds that, "Installation time savings is up to 75% with cage clamping, and time is money."

Quo vadis, distributed I/O?

Charles Cook, PE and product manager, advanced electronics for Wago, sees distributed I/O systems giving designers more choices for efficient, flexible production. Here are some of the industry trends he is seeing with his customers.

Compact and lower cost. "They really want compactness with low cost. Some are looking at lower priced systems but don't see the quality they expect. Customers want to populate existing cabinets with more I/O points-packing more information in the same system space, at the same price as ten years ago!"

Additional features. "What else can we do with this, they ask. How about features such as control, network connectivity, programming, and local data processing without expensive connections to a network to distribute the result?"

Intelligence for the future. "What will I be able to do with this in the next year, or two, or three? In other words, how is the product going to evolve in local processing, and processing more information at higher speed? It's not so much an issue of backwards compatibility but, say, taking today's system and allowing addition of a specialty node, such as a vision system. Such upgraded functions will exist and talk on the same network without the network noticing the difference."

And how important is speed? Cook says one customer told him that just by cutting processing steps in a multi-step process that turns out hundreds of thousands of parts per day, from about 3.5 to 3 msec each, they could eliminate buying one complete $400,000 production machine and still maintain required output.

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