It's a Wireless World

Nissan's automobile and truck assembly plant in Smyrna, Tenn., recently implemented a wireless control system upgrade to an existing conveying system. The conveying system moves rear-axle assemblies of two and four-wheel drive trucks from one operator station to the next via a monorail (Figure 1).

There are four "transporters" on the monorail. Each transporter is a hoist-and-trolley assembly using a custom-designed tool that carries a rear axle. A soft logic controller coordinates movement. Operators are stationed at four locations, each performing a specific task as part of the assembly process.

The four soft logic controllers are networked back to a central control station. Communications among the controllers is via a wireless communicator module, which enables communications directly with the controller backplane. The wireless modules communicate with each other via a 2.4-GHz spread-spectrum wireless link.

Metrolina Ergonomic Solutions (

Metrolina designed and fabricated the transporters and supplied the Demag Corp.-built monorail hoist and drive systems. Metrolina and Demag designed the entire conveying system. The wireless control system was designed, installed, and commissioned by Metrolina.

No special programming was required for the communication link because the wireless communicator module is recognized and used by the soft logic controller as standard I/O. "Implementation by a PLC programmer is fairly simple and straightforward, as there is no proprietary software or hardware to configure," says Ben Brechtel, technical sales engineer with Control Chief (

Control Chief develops wireless remote control systems for industrial environments. The company believes that for safety, reliability, and productivity, many industrial operations and equipment are best controlled from a safe distance via a wireless link. Control Chief supplied the wireless control hardware for the project, and also participated in the PLC software development.

"Before the system was upgraded with wireless automation, each operator manually maneuvered the axles from station to station," says Brechtel. "The new system is more efficient and requires less human effort." He says production with the new system has increased while maintenance of the equipment has decreased, producing a more cost-effective and profitable operation.

Nissan found the entire axle transport and assembly operation could be operated with one less person. "That should provide a two-year payback to Nissan," says Robert Koehler, president and CEO, Metrolina. "And this payback does not take into account any ergonomic issues that may have existed with the old, manual system."

The wireless solution coupled with the overhead monorail architecture also created opportunities to make other operating improvements. "Floor space could be better used for the staging of components, and operator safety was improved," adds Kohler. "The wireless system enabled the operators to focus on their required tasks at the workstations and eliminated the need for the physical manipulation of components from workstation to workstation."

Additional wireless controls could further improve operations. "Improvements to the onboard manual controls of the transporter could decrease maintenance even further," adds Brechtel. "Currently the raise/lower/forward/reverse controls are festooned from the tool up and around the hoist chain to the control cabinet and finally into the PLC. This festooning is in constant frictional contact with the hoist chain, which worsens as the tool is spun around."

As with many manual operations, inadvertent actions happen. "Unintentionally, the operators will sometimes wrap the festooned cable around the hoist chain," says Brechtel. "This causes cable wear and eventually necessitates cable replacement. A solution would be to use a wireless control pendant mounted to the tool. This would eliminate the festoon and would do away with the cost of maintenance and downtime associated with repairing the festooned cables."