Five miles of industrial networking cable running alongside high-voltage power lines 200 feet below the surface of the earth does not make for ideal communications conditions. But The Robbins Company knows how to make it work. The company boasts that owners of its tunnel boring machines (TBMs) have set world excavation records, but this Cleveland, Ohio speciality machine builder may be setting records all its own for some of the most massive and complex uses of industrial automation and networking around.
Robbins TBMs have been used for the 20-year Chicago Tunnel and Reservoir Plan, the Channel Tunnel linking England and France, and many other large-scale projects. The company’s more recent New York City Long Island Railroad tunnel project was the focus of a presentation at the CC-Link Partners Association (www.cclinkamerica.org) Conference in Spring 2012, and it highlighted the networking and automation components that go into Robbins TBMs.
Robbins was contracted to provide the TBM, conveyor systems and associated equipment for this New York City project. The project requires using a TBM to hollow out multiple tunnels 200 feet below the surface of Long Island, Manhattan and Queens. All totaled, 12.4 km of rock must be bored out, and all of the associated debris must be removed.
An elaborate system of continuous conveyors for the removal of this debris (called muck) includes every type of commonly recognized conveyor: belt conveyors, TBM conveyors, transfer conveyors, a serpentine conveyor to continuously extend the conveyor to follow the boring machine, an extensible crown-mounted conveyor, a pocket belt vertical conveyor, two cascading overland conveyors and one radial stacker.
In past operations, rail cars were used to transport material out. This method became more inefficient as the tunnel became longer. Conveyor systems improved the process, but early designs saw conveyor belts break, jumped the track, or flip and throw debris to the tunnel floor. These events occurred because of the lack of control and communication between the many conveyor motors. If one motor stopped, it would create an overload and an imbalance on the other motors because of the lack of communication between the motor controllers.
The solution to fast and efficient conveying was the use of variable frequency drives (VFDs) to control the motors. The TBMs used in New York City employed multiple 400 hp VFDs from Mitsubishi Electric Automation, Vernon Hills, Ill.
According to Chuck Masluk, OEM sales engineer for Mitsubishi Electric (www.meau.com), VFDs are located at the tunnel entrance and connected to booster drives along the length of the conveyor inside the tunnel. Because the design has long distances between motors and lots of up- and down-loading, the VFDs connect to Mitsubishi Q Series programmable logic controllers (PLCs) for load balancing. Q Series PLCs are also used mid tunnel to relay networks to extend their length.
The combination of VFDs and CC-Link communications enables load sharing among the conveyor motors. Other communication networks had been tried, but the length of the required cabling and harsh environmental conditions caused the communication system to fail regularly, said Masluk.
CC-Link networks can communicate over extremely long distances and can withstand harsh and electrically noisy environments. In the Robbins TBM design, CC-Link cable had to be run in the vicinity of the TBM’s 13.8 kV power cables, as well as near motors and other electrically noisy equipment.
“There’s very little care to separate power and signal cables,” said Masluk. “It’s not what we’d call an ideal environment for communications.” And yet, the network “works flawlessly,” he said. In-line radio antenna cable designed to leak radio signals along its length helps with communications.
Control and monitoring
Mitsubishi’s GOT1000 series HMIs are the control stations that provide diagnostics and monitoring at street level and at the TBM. CC-Link I/O is used for warning horns and lights. The CC-Link network also monitors the E-Stop functionality within the tunnel system. In the event that an emergency-stop switch is activated anywhere in the tunnel, the CC-Link network can pinpoint the activation point as well as allow the controlled shutdown of the conveyor system.
CC-Link also transmits control signals to pumps that extract water from within the tunnel using the same network as the conveyor system. Each of four pump stations has an associated camera to let operators monitor the water level there. When the water level exceeds a predetermined set point, operators activate one of two 30 hp pumps to remove it from the tunnel. Similarly, the CC-Link network enables control of six 150 hp fans that continually circulate fresh outside air into the tunnel.
The CC-Link communication system consists of three interconnected CC-Link networks working together to control the various functions at more than 70 stations, including conveyors, pumps, fans, emergency evacuation communications, and operator interface (HMI) inputs and outputs to control other functions within the tunnel construction system.
“The use of CC-Link in the tunnel boring operation has proven to be extremely flexible and versatile, with great reliability” said Matthew Gluszak, electrical superintendent for the project.
The three CC-Link Master network modules are housed in a single rack along with a Mitsubishi Q Series programmable automation controller in the main control center within the tunnel. This underground main control center is located about three miles from the main engineering offices, which are outside the tunnel in Queens. It houses the control panels for the conveyor drives, and the HMIs to monitor the operations within the tunnel system.
While the main control center in the tunnel communicates with the engineering offices in Queens, it also coordinates communications three miles into the tunnel to control the two networks that travel to the TBM and control the conveyors. Even though they are controlled via separate CC-Link networks, the conveyors operate efficiently together to remove the muck from the tunnel. The networks also work together to communicate system status to the various HMIs located throughout the tunnel system.
Robbins engineers say the network “just works” despite the complex and harsh conditions. “Guys who are welding one minute are installing wiring the next,” said Muslak. “The simple screw-down terminals, the ability to add nodes without changing PLC programs, the ability to troubleshoot VFDs and I/O remotely—all of that is what they like.”
As of spring of 2012, Robbins was operating 17 large-scale projects around the world using CC-Link networks, and laying more than 250,000 meters of network cable in the process. Their next big project: a 100-meter water aqueduct being dug under a tiger preserve in India. Two TBMs will start at either end and evenutally meet in the middle—no doubt communicating effectively every step of the way.