Wireless I/O Streamlines Auto Plant

Carriers on Overhead Conveying System Use Wireless Radios and Controls to Coordinate and Optimize Movement and Production

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By Jim Montague, Executive Editor

More than a few people in southern Asia want to get on the road in cars and trucks.

To meet the demand of all these drivers, automotive manufacturers in India and elsewhere are ramping up production more than ever, and more often than not this involves building new factories that have enough capacity to produce the thousands of vehicles that will be needed. These automakers aren't just duplicating traditional mass-production facilities. Instead, they're leapfrogging ahead to build facilities and production lines that are more flexible and nimble than many of their predecessors in Europe and North America.

In Chakan, on the outskirts of Pune, one of India's market-leading manufacturers of utility vehicles recently built and opened a new, 700-acre, greenfield plant with state-of-the-art equipment. At the heart of the plant is an electrified monorail system (EMS), which is an overhead conveyor designed to deliver reliable, safe, quiet and efficient transportation of the chassis, engines, accessories and completed vehicles from one work station to another along the plant's assembly line, which can produce 180 vehicles per day. The EMS runs throughout the entire length of the trim, chassis and final (TCF) line of the general assembly shop. Each light truck built at this facility is transported by a wireless-enabled EMS carrier on the conveyor.

To design, specify, plan and build the new EMS, the auto manufacturer worked with system integrator Precision Automation and Robotics India (PARI, www.parirobotics.com) and distributor Yantra Automation (www.yantraautomation.com), both in Pune. Yantra is one of the largest distributors in India. The team worked closely to develop the best overall solution for this sophisticated project.

"The TCF line is the final stage in production, where components are added to the vehicle, including trim components such as windshield glass and seats, as well as operational components such as the engine and wheels before final vehicle testing," says Ajay Kulkarni, one of the leaders of the joint PARI and Yantra team.

"Because this was a new system and a greenfield plant, the manufacturer and the team weren't bound by constraints associated with some of the older monorail systems found in manufacturing plants. Thus, we were able to design a sophisticated system that conformed to the goals of the project and the manufacturer's commitment to flexible and lean manufacturing."

Teamwork on Wireless Network

The PARI and Yantra team designed a complex wireless communication system for the assembly manufacturing line, which they report was an ambitious goal in a large-scale project involving multiple carriers in continuous motion along the overhead EMS. Yantra is a Rockwell Automation distributor, so the team selected Rockwell's control solution and ProSoft Technology's (www.prosofttechnology.com) wireless Ethernet communication equipment to build a seamless and reliable communication system between each carrier and the controller, as they move throughout the Chakan plant.

"PARI was commissioned to design and implement the assembly line," Kulkarni says. "So they designed it to operate in real time (200 ms) on an EtherNet/IP control network, using several ControlLogix programmable automation controllers (PACs) and supporting peripherals on the shop floor, including I/O and variable-frequency drives (VFDs). The decision to go with ProSoft's Industrial Hotspot radios was made primarily because they support the factory's Rockwell-based controls and communication interfaces seamlessly."

Movement of the EMS carriers for transporting vehicles through the different stages of assembly also is handled via wireless EtherNet/IP. "The control system consists of one PAC on the conveyor and one PAC on engine decking system for body marriage," Kulkarni adds. "The conveyor PAC is hardwired to two ProSoft master radios, while the engine decking PAC is hardwired to a third master radio. The conveyor PAC connects wirelessly with 33 individual carriers along the EMS, while the engine decking PAC connects wirelessly with three engine carriers. Each independent EMS carrier has a local control panel with I/O points and a VFD, while an access point acts as a repeater to establish wireless communication between the main control panel equipment and their respective PAC. The carrier radios communicate with each other and with the master radio." (Figure 1)

Kulkarni explains that the Chakan facility's EMS application is time-critical, so each repeater radio is in constant contact with its parent master radio to avoid switching delays when communications change from one master radio to another while the carriers are in motion. "The master radio in each conveyor PAC has two Omni antennas with a splitter to deal with multi-path fading effect," he adds. "This architecture fully supports seamless roaming by the carriers."

Success and the Future

After some challenges with line-of-sight issues, which were resolved by adding another master radio and elevating all of their locations, the wireless EMS now provides real-time communication between its carriers and the PACs on the assembly plant floor, including real-time I/O status for conveyor movement control. The system also enables wireless synchronization between the floor-mounted engine trolleys and the overhead EMS carrier, which aids smooth decking of the engines.

"The flexible architecture also permits independent operation of each vehicle carrier, enabling carriers to be programmed for different speeds based on their location on the conveyor path," Kulkarni says. "The conveyor speeds are switched seamlessly in the process zones, transit zones, straight and curve zones, manual speed zones, and slow-and-stop speed zones."

The completed EMS project went live in November 2009, and since then the auto plant has seen an increase in uptime, reliability and consistency in production output, enhancing their commitment to lean manufacturing, Kulkarni says. "Because of the success of the PARI and Yantra team, this auto plant is installing five more similar applications consisting of both an EMS conveyor system and material handling in the other vehicle assembly shops." 

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