Going mobile with sensors

Wireless sensor technology may be the next frontier to get more data from more points in the supply chain.

By Bob Trebilcock, Editor at Large -- Modern Materials Handling, 12/14/2007

Sensors—those little devices that look for cartons on a conveyor and monitor the vibration on motors—just could be the next automated data collection device to cut the cord and go wireless.

For those industries that rely on sensors, this could be a big boon. Wireless connectivity, after all, has been a leading contributor to productivity gains in distribution centers and factories. Going mobile enables workers to take bar code scanning, label printing and voice technology directly to the point where the work is getting done. RFID, meanwhile, completely automates the data collection process.

Why most sensors need wires

Until now, however, sensors have still required wires to do their job, especially in automated materials handling applications. There are two reasons for that.

The first is a phenomenon known as information latency—that is the speed at which information travels through a wire compared to the speed at which it travels through the air. “A wireless mesh network is transmitting 100 to 200 millisecond data rates,” says Cliff Whitehead, manager of strategic applications for Rockwell Automation. “That sounds fast, but a motion control application, like a high speed conveyor and sortation system, requires faster data rates than that.”

The second is the need for power. While a sensor monitoring the fill level in a tank may only need to come on for brief periods of time at spaced intervals, a photoelectric eye on a conveyor traveling at 600 feet per minute “is going to be on all the time and needs power,” says Whitehead. “If you’re going to the expense of running power to the sensor, you might as well put a signal cable in as well.”

Emerging applications for wireless sensors

There are, however, some wireless sensors already on the market for materials handling applications. Banner Engineering, for instance, has developed wireless sensor solutions to detect the presence of automotive doors on an overhead conveyor system in an automotive assembly line and to monitor motor and bearing temperature in an automated storage and retrieval system.

Two developments are making these new applications possible:

The first is a power management system. “The key is to efficiently power the sensor, or cycle it on and off, in a way that extends the battery life,” says Darvin Kaelberer, Banner’s wireless business development manager.

The second is the development of wireless mesh networks to communicate data. In a mesh network, intelligence is built into the sensors in way that allows them to organize a network and hand off information from one sensor to the next, like a bucket brigade, until it reaches a centralized gateway that’s connected to a network. “The sensors figure out the best way to get that information back to the gateway,” says Robert Shear, director of market development for Dust Networks.

While the technology is marching forward, most experts still believe broad-based implementation of wireless sensors in automated materials handling will be some time off. “For now, status monitoring, especially in process manufacturing, like an oil refinery, is the most common application for wireless sensors,” says Shear. “Things happen a little slower and an information infrastructure is already in place. You’re just adding more sensors.”

To learn more about wired and wireless sensors, look for the Equipment Buying Guide in the January 2008 issue of Modern Materials Handling.