Modular conveyor uses new I/O communication design

Comau-Pico Powertrain Systems (Southfield, MI) is a supplier of automated assembly and test equipment systems serving major vehicle manufacturers in the automotive powertrain market. Its customers requested significant improvements in overall value of purchased conveyor systems. A year ago, Comau-Pico made the decision to design a completely new conveyor system for transporting automotive power...

09/01/2002


Comau-Pico Powertrain Systems (Southfield, MI) is a supplier of automated assembly and test equipment systems serving major vehicle manufacturers in the automotive powertrain market. Its customers requested significant improvements in overall value of purchased conveyor systems. A year ago, Comau-Pico made the decision to design a completely new conveyor system for transporting automotive powertrains. Donald Wyman, chief controls engineer, and Thomas Hunt, senior controls project engineer, set out to create their "New Global Standard Controls Architecture."

The goal was to significantly reduce down time and life cycle cost of the system. Messrs. Wyman and Hunt knew that in order to meet their customers increasing needs they would need a completely new approach.

In addition to the major project goals, they had some goals of their own. They had always wanted a system that was modular and scalable. This would allow them to reduce design time and time on their shop floor. Explains Mr. Wyman, "Shorter design and production cycles allow us to increase sales using our existing resources."

The new conveyor system would require open distributed network approach. The system must be network independent. "End users will specify DeviceNet or Profibus. We must be able to easily support both," Mr. Hunt points out. Another key element was the use of quick disconnects. "We used quick disconnects where ever possible. Quick disconnects reduce startup and test time. They also make trouble shooting and modifications easier," adds Mr. Wyman.

Distributed design

Distributed design moved all motor control and associated I/O devices out of the main cabinet. The new main cabinet was less than 1/4 of its original size. It basically is a point for power distribution and e-stop components. I/O devices and motor control components were distributed out to small cabinets along the conveyor. Each small cabinet contained one motor starter, a safety disconnect, a variable frequency drive, and a few local digital I/O points. This created a modular conveyor section.

"Putting all the controls for the motor near the motor works out great," notes Mr. Wyman. "With the old design, we would run into distance limitations with the variable frequency drives (VFDs). The motors could not be more than 100 feet from the main cabinet where the VFD's were located. This limited the overall size of the zone. With the new design, the size of the zone is unlimited. Furthermore, having the VFD's right next to the motor has eliminated some of the noise issues we used to see with longer cable runs".

Trouble shooting the new system is significantly improved. The old system typically required at least 2 electricians, one at the main cabinet and one near the fault to find for example an open I/O circuit. Wire replacement could take hours. Now, I/O wires are just a few feet long easily handled by one person. A faulty cable can be replaced in minutes rather than hours.

Each of the section control cabinets required I/O modules within the cabinet and external to the cabinet—internal for motor contactor and stack light signals and external for proximity sensors on the conveyor. But there was no product like this could be found. So, they turned to InterlinkBT (Plymouth, MN). Within a few days a rough concept of a Profibus station with internal and external I/O points was hammered out. "We were literally 'Thinking outside the box'," said Mr. Hunt. "So, we decided to mount the Profibus station on the outside of the cabinet."

"We are very pleased with our 'New Global Conveyor Solution'," relates Mr. Wyman. "It has exceeded our expectations. The modularity of this system has paid out many dividends. It is easier for the customer to maintain and troubleshoot. And, It is easier for us to design and build. It's a 'win win' and it will be our standard for the foreseeable future. "





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