As a manufacturer of custom automation for a diverse clientele, we pride ourselves on innovation and customer support. So when we were asked to design an easy-to-modify system with 12 workstations and a multitude of I/O, we were excited to take on the challenge.
Keeping with our philosophy of flexibility, we designed the mechanical system around an 8-m power and free conveyor because its modular design featured standard catalog components that made it easy to assemble and take apart.
Creating an electrical control system with the same versatility was another matter, because the 12 process stations contained more than 100 discrete I/O points that needed to be routed back to the control panel.
A bus system seemed the most logical solution, so we talked with several vendors. The problem was our assembly was based on discrete sensing,we simply needed to read inputs and set outputs. While some of the upper-level buses may be ideal for sophisticated control with advanced diagnostic abilities, those systems clearly were overkill for us.
Soon thereafter we were introduced to AS-Interface, a bit-level system that connects discrete and analog devices to a controller. As a 30 VDC system that accepts any topology for cable lengths up to 300 meters, AS-i offers 5-msec update time for a fully loaded system. AS-Interface also is deterministic, so we could calculate response time by knowing the number of I/O modules attached.
The feature that sold us, however, was its universal nature. AS-i works with just about everything. "We didn't want to be locked into proprietary technology," said Toms Pino, our senior design engineer. "When we learned that AS-i operates with any brand of sensor and integrates seamlessly with A-B PLCs, we knew it was for us."
A Pepperl+Fuchs engineer walked us through the setup. Installation is essentially a three-part process: attach the modules near the I/O points, lay the flat cable, and then address the modules. For network configuration, we recommend a utility called the G-File Wizard that connects AS-Interface with an A-B SLC 500 master and stores the AS-i configuration in RSlogix software. The G-File Wizard is available free at www.cnet.com or www.am.pepperl-fuchs.com.
AS-i makes it easy to add I/O to our systems,we just attach a module to the existing cable, and then add that module to the configuration. Replacing a module can be done while the power is on because the system automatically addresses the new module. "If we needed to add a sensor, we just attached it to an existing module," said our manufacturing supervisor, Leon Dunlap. "We didn't have to worry about how we were going to get the wires back to the controller."
There are situations when hard wiring is still the best option. That's the case with assembly systems we design around small rotary index tables. The circular shape ensures that no output device is beyond 2 ft. from the center, so as much as we preferred cable-connected modules, it was faster and less expensive to wire sensors directly to the PLC.
We received an immediate return on our investment by cutting our planning and installation time in half. In addition, we estimate that we reduced material cost for wiring by almost two-thirds.
Some benefits, such as a reduction in planning time, are difficult to quantify, but important nonetheless. With 496 I/O per card, AS-i reduced a 13-card setup to just two cards,one for the processor and one for the AS-i card. And because we build our conveyor systems in sections--we remove the AS-i cable when we disassemble the machines for shipping--the single cable makes assembly easy.
AS-Interface enabled our company to create a product that offers manufacturers greater control over their processes. Many companies are afraid of investing in automation because requirements constantly change, so companies fear a system could be obsolete the moment they place an order. To alleviate that, we design our systems for easy modification. Mechanical segments are small enough to change on short notice, and AS-Interface enables our engineers to quickly add or subtract process controls.
Our success depends upon how we respond to customer needs, so selecting the right technology is paramount. AS-Interface meets our criteria by offering affordable technology with proven function.
Steve Benvenuto is senior process engineer at Performance Automation Inc., Boca Raton, Fla., a designer/builder of custom machines, assemblies, and process automation systems. Learn more about them at www.performanceautomation.net.
