Bridge cranes are the workhorses in heavy industry facilities around the world, lifting massive loads that are either production inputs or outputs of products manufactured in a plant. For example, the metals industry uses these cranes in all stages of production – from pouring feedstock into furnaces to loading 60-ton coils onto inventory racks or finished goods onto trucks or rail cars.
One of the world’s leading sources of controls for these cranes is Trutegra, a supplier and integrator based in Charlotte, N.C. Founded in 1990, the long-time Siemens customer provides a wide range of control and automation systems for industrial applications.
Trutegra surveyed many of its customers to learn about the ongoing safety issues they were incurring for crane and hoist controls. One major issue was that bridge cranes accidentally bump into various objects or structures as they moved along their work paths. These bumps also cause substantial maintenance and downtime costs.
“The problem is a chronic one that can have huge, if not grave, consequences,” says Paul Vogt, Trutegra’s vice president of Research & Development. “If a significant incident occurs, plant downtime can be in the millions of dollars and lives could be at stake.”
The sheer size of bridge cranes and their massive loads means accidents are never minor. A crane’s overhead bridge can be as high as a six-story building. Its length can span 100 feet or more. A trolley positioned on the bridge typically runs on rails that can extend the length of six football fields. Finally, the trolley has a massive hoist system to lift loads. In many cases, the crane includes a rotating mast in combination with its hoist, which lets the crane rotate a load.
Together, these components form a system that allows the crane operator to grapple and move massive loads quickly and effortlessly around a facility. The cranes may be manual, semi-automatic or fully automatic, with the trend toward the latter.
Many of Trutegra’s metal industry customers use bridge cranes with rotating masts that have hoists with a “horn” to lift huge coils of metal. Crane operators move the coils at three meters per second through spaces that have as little as eight inches of clearance. Coils are moved from the end of the plant’s production line to a row of racks, where they make a 90-degree turn into a 12-foot aisle. They are then moved to an open rack space and deposited.
When a large crane hits something, tremendous forces are transmitted to its mechanical components. Even the slightest contact between the load and the rack structure or another load can generate enough impact to damage the gearbox that drives the mast rotation. Replacing or repairing these rotational axis gearboxes takes significant time and costs thousands of dollars.
The Trutegra solution is a precision, laser-guided obstacle avoidance system that uses Siemens S7-300 PLC and SIMATIC Nanobox PC technologies. It’s the basis of a precision, laser-guided obstacle avoidance system (OAS) that prevents the crane from touching obstacles, whether it’s controlled manually or automatically by computer. The solution is so unique that Trutegra has applied for a patent.
Trutegra’s OAS solution works in three steps:
- First, the system maps the obstacles in the work area using a CAD drawing. The drawing is converted into an efficient database format, and is stored on a Siemens SIMATIC Nanobox PC.Trutegra chose Siemens Nanobox because it is an industrial-grade, maintenance-free PC with a powerful, energy-efficient Intel Atom E6-family processor. It communicates over wireless Ethernet to a Siemens S7-300 PLC that helps the operator control the crane’s motion.
“Siemen’s compact Nanobox was ideally suited for the factory floor application, because it’s powerful, has no moving parts, is fanless, rugged, well-priced and it mounts on din rail,” Vogt says.
- Second, Trutegra maps the size, shape and velocity of the crane and its load. It then uses laser-enabled distance meters, encoders and other means to monitor the real-time position and velocity of the crane. These devices help the OAS determine the crane’s position to within millimeters.
- Third, using high-speed calculations afforded by the Nanobox PC, Trutegra’s OAS server does the calculations needed to predict future collisions. The system intervenes “on-the-fly” to rapidly decelerate the crane, if it detects that the crane is traveling along a vector that will result in a collision.
Preventing collisions. The Trutegra OAS software can override manual or automatic control if the crane gets too close to an obstacle. When needed, the OAS automatically slows the crane as it nears the obstacle. The algorithm that controls the braking action is sensitive to the dynamically-changing conditions of the crane, which includes speed and the size and orientation of the load.
For example, one combination of variables might start slowing the crane at a distance of twenty meters while another set might begin to intervene at half that distance. “If an operator has the crane a half a meter from an object and wants to nudge the crane a bit closer to the object, the OAS will permit that because it knows the crane is moving very slowly and can stop,” Vogt says.
Siemens provided training and support in the development of the Trutegra OAS application. Vogt notes that the open architecture of the Siemens S7-300 PLC and the Siemens SIMATIC Nanobox PC enabled his programmer to develop the solution built on a third-party application and using XML. The use of open standards lets Trutegra use the solution with other vendors’ PLCs.
Crane customers report that the new technology succeeds as a productivity-enhancer because it allows operators to execute crane operations faster. “They can operate at higher speeds because they know the OAS will slow the crane down.
Downtime and costs due to mechanical repairs to components such as gearboxes are all but eliminated because the OAS prevents even small collisions. The OAS also mitigates collision risks to other plant structures, reducing damage that could compromise plant output and incur the huge costs of production delays. Above all, the customer’s plant operations are much safer than before.
“This is especially true in industries that use large equipment like bridge cranes. Trutegra’s OAS solution using the Siemens SIMATICS Nanobox PC and its PLCs can provide an important margin of safety by reducing dangerous crane collisions,” Vogt says. “More importantly, the operating environment is much safer for crane operators now as well as for everyone working around the cranes. After all, you can’t measure the value of human safety.”
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