For most people, theaters, art exhibits and amusement parks are all about having a little fun and enjoying the finer things in life. For automation professionals, these venues are about applying rugged technology and enforcing safety practices. For them, entertainment engineering is a sophisticated business.
Bosch Rexroth was one automation company that discovered this when it ventured into the stage drives-and-controls business. It happened during a renovation of the city auditorium in its hometown of Lohr, Germany. Since that project back in the 1970s, the company’s technology has grown from a marginal product line into an independent business on the worldwide stage.
A recent claim to fame was Bosch Rexroth’s role in the six-year renovation that transformed Moscow’s Bolshoi Theater into one of the most technically advanced theaters in the world. Since the project was completed in 2011, 600 electric and hydraulic drives have been playing their parts quietly under the crystal chandeliers and behind the golden façade of Russian classicism. They have been raising and lowering seven dual-level platforms that make up segments of the 520-square-meter stage, and 220 hoists above have been lowering and raising scenery. The touch of a button initiates a pre-programmed, synchronized sequence of motion that moves sets and groups of people noiselessly.
The people riding the platforms and working under the moving loads illustrate a key difference between industrial and entertainment automation. Workers—and the customers themselves, in the case of amusement park rides—are interacting with the moving components, making safety the primary design criterion in the entertainment industry. It is not an afterthought, as is all too often the case in manufacturing. In this evironment, safety trumps uptime, reliability and even cost.
At the Bolshoi Theater, a sensor network and control software provide an important line of defense for the actors and prop hands. Also important is a carefully thought-out, fail-safe design. “You have to know what a failure at any point in the system is going to do to the output,” says Greg Gleason, hydraulics special technologies manager at Bosch Rexroth. “If somebody is on a platform supported by hydraulic cylinders and something doesn’t work right, the design must ensure that the platform isn’t going to fall or cause an abrupt, uncontrolled motion.”
The show must go on
Another ramification of the close proximity of the consumer to the production equipment is that reliability is the second-most important design criterion in entertainment, following closely behind safety. There are no work-in-process buffers, warehouses or retail outlets between most entertainment venues and their customers, as there usually are between manufacturing lines and consumers of manufactured goods. Consequently, the equipment must work when customers are assembled in the theater to watch a performance or when visitors to an amusement park are ready to ride an attraction.
To ensure safety and reliability, the specifications in entertainment contracts, especially those for theme parks, are very involved. In fact, Gleason reports that they are often far more demanding than military specifications. “An attraction has to be designed and built to run 16 hours a day, 364 days a year,” he says.
For this reason, high-end engineering companies have been developing simulation tools to help their engineers design safe and reliable equipment. A set of proprietary simulation tools used by engineers at Bosch Rexroth has been especially helpful when the applications involve large masses and aggressive accelerations and decelerations. When a cylinder retracts very quickly in a highly dynamic application, the fluid can flow into the return line with a force that can affect the operation of the cylinder and, in some cases, damage it. The software helps designers analyze the flow and alleviate those constrictions.
The automation vendor’s researchers also use these tools and physical tests to guide them in reacting to the trend toward using increasingly powerful drives on stage equipment. Machinery operating above a stage can now move as much as a ton at 1.8 m/sec. Because emergency stops can generate loads twice as high as the nominal load, the load-bearing components must be strong enough to withstand the shock. Another part of the system can be a hydraulic damping device that the engineering staff developed for electromechanical winches.
Precision is an art
Although safety and reliability are the two top performance requirements for most entertainment engineering, precise motion control is often a third. For theme park attractions that people ride in the dark, for example, the motion must be synchronized exactly with the audiovisual presentation. Slight lags can nauseate riders who are susceptible to motion sickness, according to Linda Freeman, senior sales engineer at Rockwell Automation.
With precision affecting customers so directly, the entertainment industry relies considerably on sophisticated motion-control technology. In fact, the complexity of motion-control applications found there rival those in manufacturing. Both have their simple applications that need only directly driven asynchronous motors or frequency-inverter-driven motors. “But both also have applications with complex kinematics for movement that requires precise motion control with servomotors,” reports Michel Matuschke, vertical market manager for stage and show technology at Beckhoff Automation.
When it comes to the number of axes on an application, though, entertainment wins a Tony. “In a manufacturing setting, a really big machine could have 60 axes of motion; an especially complex one may have up to 100 axes,” Matuschke says. “In the entertainment industry, however, we have seen recent applications with hundreds—even over 1,000 axes—on one machine.”
|In a kinetic sculpture for Lundin Norway, controls from Beckhoff Automation coordinate the 529 servomotors that raise and lower the Plexiglas tubes to simulate undulating waves in the ocean. Sensors drive the rods upward to a safe position to allow visitors to wade into the waves. Source: Beckhoff Automation|
A good example is the kinetic art that has enjoyed a measure of popularity lately. There are 529 servomotors in the “Breaking the Surface” exhibit that Oslo-based oil company Lundin Norway commissioned to celebrate its 10th anniversary. Control technology from Beckhoff Automation coordinates the motors that raise and lower 529 bright-orange Plexiglas tubes in a way that simulates undulating waves in the ocean.
Complicating the control challenge, designers at the Scandinavian Design Group created the kinetic sculpture to interact with visitors. Based on feedback from capacitor sensing in the floor and four cameras hanging in the corners, the tubes retreat upward into a safe position as visitors dive into the exhibit and wade through the waves.
The PC-based control architecture responsible for generating this motion relies on primary components at three main levels: sensors and EtherCAT terminals at the sensor and actuator level, four C5102 industrial PCs at the PLC level, and software at the superordinate application level.
Beckhoff's EtherCAT-based fieldbus has the speed to process the 10,200 connection points in the system. TwinCAT NC point-to-point axis-positioning software performs the interpolation necessary to create the undulations, calculating the position of each tube within 1 ms. The set values for the designers’ 3D motion profile were imported through an ADS interface from C++ into the automation software.
The modular I/O, industrial Ethernet, and flexible PC-based control architecture is a good fit for the entertainment industry, Matuschke says. The combination accommodates diverse forms of automation and their protocols, including those that this industry relies on for lighting, audiovisual multimedia, and building automation. Beckhoff can mix and match many fieldbuses because its system has incorporated more than 30 standard buses, including those used in manufacturing, building automation and entertainment.
Beckhoff credits EtherCAT technology for providing the necessary backbone. Take a fieldbus like DMX that is an industry standard in entertainment. “DMX requires 512 bytes per master,” Matuschke explains. “By using EtherCAT as a higher-level bus, we can easily implement slaves into the EtherCAT system, with each corresponding to the correct size for the application.” The communication is fast enough to transport the data effectively.
The same goes for SMPTE Timecode, another fieldbus that is standard in the entertainment industry. “We use our eXtreme Fast Control (XFC) technology to oversample this analog signal and analyze it with our PC-based control platform,” Matuschke says.
Producing a science project
Manufacturing technology is usually relatively straightforward, well established over generations. “Processing chemicals or building conveyor-based production lines has been done many times,” Freeman says. “You’re often just optimizing, not trying something revolutionary on each project.”
Amusement parks, on the other hand, have moved beyond simple rollercoasters and rotating rides—today’s attractions incorporate creative content to add to the experience, like fire, gas explosions, or a combination of heat, humidity and rain. “So new attractions are often more like science projects,” Freeman observes.
Another range of unknowns that engineers must deal with in entertainment is the human cargo itself. “In a manufacturing plant, operators of different heights and weights don’t affect the control system,” Freeman notes. “On an amusement-park attraction, however, the control system has to be able to accommodate the varying weights of people on the vehicle.” And how the riders will interact with the vehicle is also unpredictable.
The engineers tasked with making the creative idea a reality need a thorough understanding of the physics behind both the motion itself and the control mechanisms. They also need access to the appropriate simulation tools, the use of which has increasingly become a best practice over the past few years for these kinds of projects.
For example, a user can import a SolidWorks 3D model and an Excel file of motion-profile data into Motion Analyzer and simulate a motion application. “If you can model the forces and heat in a mechanical system over time, then you can properly size the motors and the control system,” Freeman says. Simulation also makes it easier to perform what-if scenarios to ensure that the motion control system can deliver the desired creative content.
Wireless tracks a dark ride
In one case, Freeman and her colleagues at Rockwell Automation used their Motion Analyzer simulation tool to improve the economics of a new ride that was going to run at high speeds in the dark. The simulation helped the design team deal with many of the unknowns so it could right-size the automation. “We were able to take much of the guesswork out of the project on the front end through simulation,” Freeman says.
Another tactic for eliminating guesswork is to conduct a proof of concept. In one example, the goal was to minimize the amount of wiring for the sensors without compromising safety and reliability. Because the vehicles traverse a substantial distance within a very big building, connecting the sensors with wires would have been costly.
To avoid this expense, the park’s technical staff decided to try wireless technology. “No one had done this before,” Freeman says. “So the challenge was maintaining safety and tracking position in a very high-speed environment.”
Rockwell worked with the ride’s design engineers to simulate the control system and then conduct a live test on an existing attraction. After the simulation and proof of concept, more of the unknowns became known, and the final design could be created. The Rockwell engineers also assisted during installation to adjust the configuration for the operating environment and to conduct tests to make sure that it performed to specification.
Even then, there is still guesswork involved for predicting the longevity of components. As a result, a new attraction will remain a science project for several years after being put into service. “Variations usually don’t become predictable until you have two or three years’ worth of operating data,” Freeman explains. “Sometimes, it’s not until a ride has been built and running for a while in the heat, vibration and other environmental conditions that you really start to learn what can cause a component to fail.”
When variable-frequency drives (VFDs) failed prematurely at one theme park, Rockwell brought in materials scientists to conduct tests onsite and in the lab to identify the root cause, which turned out to be brake dust. “Our solution was to put a special coating on the boards in the VFDs so the brake dust wouldn’t cause shorts,” Freeman recalls.
They were also able to apply the lessons learned to manufacturing. “We realized that this solution is probably good for other industries,” Freeman says. “So we made the coating a standard feature when our new product line came out.”