Hulking Automated Guided Vehicles Offer Wireless Flexibility

A recent Sage survey released in March reveals that 46 percent of factory operation managers are investing in resources to support top priorities, namely higher production rates. Automation technology could be a factor in that high investment rate, enabling new applications like wireless automated guided vehicles (AGVs) to make it to the factory floor.

Fori Automation (www.foriautomation.com) produces many types of AGVs, including traditional vehicles tethered to traditional interfaces, for the aerospace, automotive and defense industries. Its customers are starting to understand the possibilities of wireless control.

“End users are exploring new manufacturing and assembly processes, and material flow, with AGVs,” says Greg Stegner, a Fori Automation controls project engineer. They are now able to maximize available floor space by avoiding “the traditional monuments created by traditional conveyance or transport systems,” he says.

For example, one Canadian aircraft plant, with 150,000 sq. ft. of production space, has 2,500 ft. of magnetic bar laid in the floor to guide its 18 AGVs. These vehicles operate simultaneously, carrying or towing large subassemblies for production.

Elsewhere, AGVs increase delivery speeds for a 30-ton, 60-ft.-long wing at a Lockheed Martin aircraft plant, helping to speed production. But faster production alone is not the priority with end users using AGVs. The introduction of wireless AGVs lets plant managers gain operational flexibility and the ability to put more vehicles on the plant floor. The goal—and result—is meeting higher production targets.

“Our wireless AGVs have enabled our aerospace customers to achieve production rates never before seen at their facilities–producing more than one aircraft per day in one instance!” Stegner discloses. The company’s client list includes heavyweights such as Lockheed Martin, Bombardier, Spirit Aerosystems and Boeing, along with Mitsubishi Heavy Industries and General Motors.

Building a behemoth

The most common way to automatically guide such vehicles is via tracked guidance using a 6-mm-wide magnetic bar in a narrow, shallow trench cut into a plant’s concrete floor and covered over with epoxy. Fori Automation uses four Hall-effect sensors to ensure proper AGV positioning and accurately guide vehicles along the magnetic track in any direction.

Large AGVs from Fori Automation are 25-ton rectangular-shaped metal boxes about 40 ft. long, 15 ft. wide and 2 ft. high. Four banks of industrial batteries power servo drives, drive wheels, tooling lifters, and onboard electronics including PLCs and various control and safety sensors.

Choosing wireless real-time control was not an easy decision for Fori’s multinational companies, where security is mandatory and many impediments comprise the assembly floor. “It’s not just the floor configuration that loaded AGVs have to navigate, but also drawbridges, overhead cranes and other elevated fixtures a plant may have,” Stegner says. Plus, they must constantly communicate with other plant systems, and these communications must never be interrupted while the AGVs are underway.”

For the wireless control of its heavy-duty AGVs, Fori Automation chose Profinet as the industrial network and Siemens Industry for all automation, control and network hardware. Included in the setup was a Profisafe module that allows for safety to piggyback on top of the fieldbus layer, thereby reducing the probability of data transmission errors.

Stegner and his team chose to deploy a Profinet-based (PI North America, us.profinet.com) industrial wireless Ethernet network using the 5 GHz spectrum. Stegner says this spectrum provides much more security and far more channels than 2.4 GHz, his other wireless option—nine channels vs. three.

“Most mobile end-user devices operate in the 2.4 GHz range, so their radio interference can compromise both the integrity and security of our wireless communications,” he says. “Not only can that create control problems, but military work forbids it.”

Three-layered architecture

Stegner views Fori’s AGV system in three layers: the AGV control layer with onboard control and a separate human machine interface (HMI); a plant coordinator that plays “traffic cop” with the AGVs; and the manufacturing execution system (MES) on the back end.

Both safety and control devices communicate via Profinet to a Siemens (www.usa.siemens.com) Scalance X switch that’s connected to a wireless client. This onboard client then communicates over the 5 GHz spectrum to fixed-mounted access points located in regular intervals throughout the plant. These points are usually in a plant’s rafters or ceilings for maximum range, and overlap with radio signaling to prevent any coverage gaps.

Fori leverages Siemens’ Industrial Point Coordination Function (IPCF) for industrial wireless real-time components for the AGVs. This builds upon the 802.11n standard for real-time control applications. Using IPCF, each wireless access point works as a “traffic coordinator” and polls clients for their I/O data in short cycles—as low as 16 ms and with roaming times below 50 ms. This lets standard data such as transport orders, status messages and failsafe communication run in parallel on the same connection.

Fori controls the onboard safety functionality with a Siemens IM151-8F PN/DP interface module with SIL 3 failsafe CPU functionality for the Simatic ET 200S distributed I/O. Together, these devices control the AGV’s warning horns and lights, E-stops, laser scanners and the pressure bumper that skirts the vehicle’s perimeter. The AGV’s guidance sensors and positioning are connected to its servo drives via contactors.

Operators provide control of the AGV using a handheld wireless panel, Siemens’ 277F-IWLAN HMI device. It offers an 8-in. diameter form factor and a thin-film transistor color touchscreen that dispenses with joysticks. The “F” model offers certified safety functionality, including an E-stop button.