Machine Design
That’s entertainment: State-of-the-art controls for state-of-the-art shows

That’s entertainment: State-of-the-art controls for state-of-the-art shows

Look backstage at a big-time theater production and you are likely to see a console like this one running a specialized control program for moving stage elements.

Picture a Las Vegas show where performers fly through the air or do backflips on moving platforms. Ten years ago, controls handling the advanced equipment involved in these feats were likely to look a lot like the programmable-logic controllers (PLCs) found on packaging lines or assembly operations. Today, that situation has changed dramatically. High-end theatrical productions are typically orchestrated by specialized software packages running on PC hardware that, in their own way, are the equal of the electronics running industrial processes.

“We don't use commercial PLCs much anymore, though the first theatrical controls were borrowed from industry,” says Dana Bartholomew, vice president of west coast operations at TAIT, Las Vegas, a supplier of staging, scenery, LED integration, show control, and automated rigging for theaters and performances. “They were functional but not elegant.”

That all changed with the development of real-time operating systems for PCs. They made it practical to write PC-based software for theater controls able to handle not just moving around stage equipment but also safety features such as overtravel and overcurrent limits.

As you might expect, controllers for theater equipment don’t use industrial ladder logic. They have their own languages. One of the most widely used theater-control programs is called Navigator, created by a firm now part of TAIT. An operator writes a control program for a theater production on Navigator by creating what are called cues. Cues are basically a list of commands arranged in order of execution. Cues themselves execute when the operator pushes a “Go” command. To the stage-automation operator, the whole show is basically a list of cues. Larger shows can use long lists of complex cues.

Operators tweak the cues all the time. “If you want something to move slightly faster, you just go in and change a cue. The change would only take a few seconds,” says Bartholomew. “Back when we used PLCs, you would have to change the PLC programming and that process got to be quite time consuming.”

Of course, every show has its own special stage equipment. So before the first cue is ever written, TAIT personnel write rules into the control program to prevent mishaps. “When we commission a system, we have discussions with the theater staff about events that must never happen,” says Bartholomew. “We write rules into the software that stop cues from creating these scenarios.” But rule writing is an ongoing task. “As the show rehearses, you learn about other possibilities you did not foresee. So a show may start with 100 rules and end up with 200 after it has run for two years,” he explains.

For a simple example of a rule, consider a stage containing an elevator and a scenic element that moves back and forth. “Before theater automation, you counted on the operator knowing enough not to move scenery across the stage when the lift was down so it didn’t get dumped in the hole, or not to move it when the lift was up so it didn’t run into the side of the elevator. Now, we write a rule that says if the lift is not at stage level, the scenic element can't move into the elevator zone. If the operator tried to write a cue that violated that condition, the rule would prevent it from happening,” explains Bartholomew.

There are additional safeguards built into the controls to keep people on stage out of harm’s way. “During a show, performers and stage personnel can be in zones that are potentially dangerous, though it is all very-well choreographed,” says Bartholomew. “To build in safety, we incorporate features such as dead-man switches for lifts or other conveyances that carry people. The controller would let things move as long as a technician holds down that switch. If there’s a problem, the technician lets go and everything stops.”

All this talk of dead-man switches and safeguards might give the impression that automation suppliers are preoccupied with safety. That impression would be correct. “The theater industry has tried to be proactive about safety partly because people have to work in high areas where there are no guardrails. So it is pounded into your head that safety is of utmost importance,” Bartholomew explains. To that end, the industry has its own safety standards body, PLASA, which runs an ANSI-accredited program for developing standards and recommended practices for safe working conditions. PLASA’s working groups focus on such areas as camera cranes, control protocols, electrical power, fog and smoke, performance floors, photometrics, rigging, and stage lifts.

Of course, not all events require controls able to handle a Cirque du Soleil production. Smaller venues still use simple controls such as across-the-line starters that move curtains until a contactor opens. More sophisticated variable-speed drives and drives that move stage objects based on position feedback are used as well.

But all these systems need to be run by experienced personnel, and these individuals are increasingly rare. “In the past, theaters could afford to do on-the-job training. Now, that doesn't happen very often. You need the right background to get a job in the industry these days. And it is hard to find high-quality skilled people. Only a few schools have programs for automation operators,” Bartholomew says.

To help fill the personnel gap, TAIT runs students from the Stagecraft Institute of Las Vegas through an introductory course on theater automation and conducts four-day training schools for operators of its Navigator software. But that kind of exposure doesn’t prepare students for handling high-end Las Vegas productions. “Even after taking that four-day class you wouldn't be able to go out and program for a high-level show. You would be able to watch a show that has been programmed and understand the cue structure and how it was handled,” Bartholomew says.

Few people get into theater automation by the route Bartholomew himself took, starting in 1984 as a stage hand for the rock group Mötley Crüe. “I am one of the last of the guys who had some lucky breaks. I rode the coattails of automation through the industry,” he says.

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