Wireless Helps Avoid Collisions
With sophisticated processes involving multi-million dollar cranes operating at rapid speeds while carrying several tons of materials, crane collision is a clear concern. It is not just the cost of downtime and repair, safety of crane operators and workers at ground level is critical as well. For three multi-crane installation projects, system engineers at Andritz Inc. felt that a wireless Ethernet was the only way to achieve a reliable, high-performance anti-collision system.
In Roswell, GA, residents make their way down tree-lined brick walks of the city’s Historical District, sipping their morning coffee from recycled paper cups, gazing at furniture through shop windows. Just outside of this city, Andritz Inc., an international provider of services and equipment for the world’s creators of pulp, paper, tissue and oriented strand board (OSB) products needed to create a system that would allow two portal cranes to work independently and simultaneously while sharing a common set of two perpendicular rail tracks.
With more than 150 years of experience, Andritz is able to support pulp and paper companies with a complete top-to-bottom custom integration process. Andritz provides equipment for the processing of tree-length logs using debarking drums, chippers, conveying and storage systems, refiners, pulp drying lines and tissue paper machines that form, press, dry and reel the finished product. From start to finish, these applications are designed, set up, programmed, delivered, and installed by Andritz for the customer.
Andritz received commissions to build three different pulp and paper projects, including a total of six portal cranes. Each project required the supply and installation of two cranes for unloading logs from logging trucks and transporting them to an onsite woodyard. This system would enable the two cranes to travel from the log truck unloading area to the woodyard infeed equipment or to the log storage area located in between the two rails.
Andritz portal cranes are capable of lifting an entire load of tree-length logs from a logging truck with a single bite of the grapple. Many of these portal crane grapples can lift up to 44 tons of logs in a single bite and transport them along rail runways, sometimes up to a mile in length. Cranes traveling high speeds can safely operate up to 750 feet per minute (12.5 feet per second). A typical portal crane unloading and delivery cycle is about 2.5 minutes per crane, translating into hundreds of tons of wood per hour being processed.
Given the high performance demands of modern crane applications, the old practice of using 300 to 400 foot long bus bars or festooning cables to communicate between the gantry and trolley was not an option. Festooning cables and bus bars are costly and frequently cause operational problems. Such a system can cost $10,000 for materials alone, plus installation and maintenance costs. When equipment fails, it can sometimes take a day to repair. Such unscheduled downtime is a serious problem for the customer.
The bus bar systems operate on a serial communication network so data rates are slow, and during poor weather, particularly precipitation, the signal is often degraded. Even if the serial communication system was faster, bus bars can only communicate from gantry-to-trolley and not from crane-to-crane, which is necessary for anti-collision systems.
Each crane costs millions of dollars, and for the safety of the crane operators, it is imperative to have a reliable anti-collision system in place. Andritz needed the ability to monitor the real-time locations of each crane on the rails and to automatically slow down and stop each crane should they enter a potential collision situation. Until the advent of wireless devices, safe and reliable anti-collision systems were just wishful thinking.
Andritz placed a satellite GPS system on each crane to accurately determine their respective locations on the rail. For this to be an effective solution, each crane would need to know the position of the other crane. Andritz selected ProSoft Technology RadioLinx Industrial Hotspot Ethernet radios (RLX-IH) as its wireless solution.
ProSoft Technology’s radios provide the speed needed to transfer data between the cranes and the operators in real time. They are certified for harsh environments, making them a dependable solution despite poor weather conditions.
The main advantage of using high-speed Ethernet radio systems is that they help the cranes avoid collisions on both the network and on the track. Plus, operating wirelessly creates a significant cost savings by eliminating additional communication bus bars and festooning cables.
Altogether there are seven radios fitted to the two crane systems. One set of radios on each crane is dedicated to allowing them to communicate their GPS positions to one another. A second set of radios connects each crane’s gantry control system to its trolley control system.
The high-speed Ethernet communications are very effective, so when the crane operator moves the joysticks inside the operator cab, the gantry and trolley controls respond seamlessly, without any noticeable delays.
Finally, a seventh radio was implemented to connect the control systems of both cranes to a woodyard ground station. This ground station radio allows for remote troubleshooting, programming and operational data acquisition of the cranes. It also allows Andritz to provide remote crane diagnostics and programming support through Internet connections.
So far, two of the Andritz projects are live as of October 2006 and January 2007, respectively, while the third project is scheduled to go live in November 2008.
In application, the three wireless systems not only created a more efficient, cost-effective network than bus bars and festooning cables, but are far more reliable in diverse weather conditions. The wireless networks are self-healing, with significantly less risk of signal degradation than the alternative, and they operate in real time. These Andritz networks create a safer environment for crane operators and workers on the ground level, as well as for the cranes themselves.
|Robert Dunlop is a senior electrical and automation project engineer at Andritz Inc. Adrienne Lutovsky is a public relations specialist at ProSoft Technology. Reach her at email@example.com .|