Safely hoisting and installing 85 tons of lighting and sound equipment at the Dallas Cowboy Stadium are feats that most fans and concert-goers don’t think about when they attend events there. Yet, that was the monumental task facing the lighting contractor when the arena was under construction.
Motion Laboratories builds motor/hoist control systems for rigging, lighting, staging, and sound reinforcement companies in the entertainment industry. The company began employing load cell technology in its hoist systems. Load cells attached to the chain hoists give a real-time electronic reading of how much weight is being lifted. When lifting massive trusses, it’s critical that the weight is distributed evenly over multiple points because any one hoist lifting too much puts unequal weight on the truss. Even an eighth of an inch of uneven lift results in a substantial weight difference.
The WardeN Control unit monitors and detects weight overload or underload and stops motor movement through its interface with the chain hoist control system. It also shows the operator which channel has the potentially unsafe condition.
Prior to load cells, riggers would try to adjust the weight distribution of a truss by manually checking the tension on the chains to see if they were equally taut. While the chains may seem equally taut at first, any differences in weight are magnified as the trusses are elevated, and riggers had no way to monitor the exact load of each chain.
Motion Labs load cell product, Cell*Mate, is a combination load cell with an eight-channel Cell*Mate Hub and Cell*Mate Digital Display module. It lets you monitor both dynamic and static loads in unlimited quantities from one or more remote locations. Each load cell transmits inline force measurements to the eight-channel hub unit, which then sends all channels of data to the digital display module.
In 2008, Motion Labs wanted to take their hoist control and load monitoring system a step further. “While our Cell*Mate tells you load weights any time,” said Peter Herrmann, president at Motion Labs, “we noticed that users were spending so much time with their eyes glued to it to ensure proper loading that they weren’t paying attention to the equipment that was being moved.”
Herrmann thought it made sense to develop a product that would allow users to keep their eyes focused on the equipment and not a display. “We wanted to create a system that would control the chain hoist and monitor the loads, as well as shut the hoist control down if the loads got out of whack so the problem could be corrected,” Herrmann said. “We thought this idea would allow users to concentrate on the equipment being lifted because they would have confidence that the system would shut down if there was a problem.”
With the help of Schneider Electric and GCF, a Schneider Electric distributor, Motion Labs’ brainchild, the WardeN Control Unit, was born. This product offers many of the same features as the Cell*Mate system, but it detects any overload/underload condition and automatically stops all motor movement through its interface with the chain hoist control system. It also shows the operator which channel has the potentially unsafe condition.
Schneider Electric proposed tying in the controls of Motion Labs’ chain hoist with the M340 programmable automation controller (PAC) and Magelis human machine interface (HMI).
The WardeN continuously monitors weights and displays the data on the Magelis HMI, and it will automatically stop the chain hoists when there’s a problem. You define what percentage of weight needs to be out of proportion for the M340 PAC to stop the chain hoist, and program the PAC with that logic. The most important time to ensure proper weight distribution is when the riggers are erecting the trusses. It’s critical to ensure there is no undue stress on the building.
The WardeN system also is helpful if the equipment being hung is heavier than anticipated. The chain hoists will stop so that riggers can change the equipment being lifted or add additional points to allow for the weight.
The WardeN Control Unit lets you remotely monitor up to eight channels of load cell data simultaneously on a constant basis. The Magelis HMIs also lets you link multiple WardeN systems together so they can monitor 32, 64, or more chain hoists at one time. These smaller eight-channel building blocks can be combined to create a super grid.
“At the Dallas Cowboys Stadium, we created a 100 x 200-ft mega grid to support all of the traveling acts that perform at the stadium,” Herrmann said. “The grid consists of six eight-channel controllers. The WardeN systems watch and control the matrix of 45 points and allow for the movement of the entire grid as one unit, while also analyzing the weight/ eight-channel grid or the weight of each individual point on the truss in real-time basis.” According to Herrmann, it’s also less expensive for Motion Labs customers to tie together multiple eight-channel grids than to build and maintain a custom 32-channel unit.
Filed Under: Factory automation, Automation components, HMIs • operator interfaces • monitors, Mechanical, Motion control • motor controls, PLCs + PACs, Test + measurement • test equipment