The actors below
When the owners of the historic Kursaal complex in Bern, Switzerland, decided to undertake an ambitious modernization project in 2012, they put a great deal of thought into every detail. Among the upgrades to the Arena conference hall, for example, was a modular stage, adaptable in both shape and size. It features a state-of-the-art technical infrastructure that gives event organizers an enormous amount of design freedom.
The new Arena hall accommodates 1,500 guests and abounds in technological finesse. Although the stage's 76 square meters don't rank it among Switzerland's largest, it stands out – quite literally – with its two 26-square-meter elevating platforms and three smaller ones, each with independent control. "The platforms are powered by hydraulics," says Biko owner Rudolf Kobel. "In locations with limited space – and particularly for understage technology – the combination of compact dimensions and enormous force density makes hydraulics the clear choice." When it comes to elevating platforms for theaters, hydraulics provide additional system-specific advantages as well. Since a stage is only moved intermittently, the system is able to store energy very efficiently. "Investment costs are also a significant factor," adds Kobel.
Key topic: Safety
The understage equipment reaches deep into the Kursaal's foundations. The auto-lift alone, with five tons of lifting force, is able to raise props and artists nearly seven meters – from the depths of the hall up into the spotlight. To avoid impinging on the storage area in the basement, it was necessary to switch to a scissor lift platform. "Telescopic cylinders would also have been an option, but the scissor lift is much more elastic," explains Kobel. The auto-lift is more than simply a scissor lift platform, however, with safety requirements more equivalent to those of an elevator. "Safety is an essential consideration when it comes to retractable theater stages," says Kobel. "The machinery directives have very clear specifications on this topic." The individual podiums must be free of pinch points and prevent falls from higher than 1.6 meters as well as unintentional platform retraction. The control system required to ensure these measures is more involved than that of a typical platform lift. "A two-channel design, for example, prevents hazards such as the stage being lowered while a door is open," says Kobel.
Biko has planned and built more than 500 such stages. "These are all special-purpose applications," says Kobel. "We can't compete with the prices foreign competitors offer for standard platform lifts." For previous lifts – including an 80-ton platform used to lift a tank – the performance offered by small controllers has been sufficient. In Bern's Kursaal, Biko opted for a controller from B&R. "The application isn't that complex, but there are a lot of inputs and outputs," explains Christoph Hofer, who is responsible for controllers at Biko. Biko is no newcomer to B&R products, however. The company has been using B&R controllers in laundry applications such as folding equipment for clothing and textiles for over 20 years. "I still remember the black series," says Kobel, referring to B&R's now retired family of Multicontrol, Midicontrol and Minicontrol devices – visionary technology in its day. "We were the first in the laundry industry to use B&R controllers – and now 95 percent of the global market has caught on. B&R was also the first to bring a real-time controller to the market. When we were first looking at B&R, the only competitor even close in terms of speed was Mitsubishi, but B&R was stronger in HMI. I think, overall, B&R is simply the most consistent supplier of the most innovative control technology around," praises Kobel.
The control unit
Software developer Christoph Hofer shares Kobel's enthusiasm based on his positive experience using B&R's Automation Studio development environment. The control unit consists of compact X20 I/O modules and a Power Panel 45 with integrated logic and drive control as well as a 5.7" QVGA touch screen. As far as Biko and Rico Wagner, the head technician at Bern's Kursaal, are concerned, this is the optimal control and HMI solution. Using the optional interface cards, it is also possible to connect other B&R products or even to integrate the Power Panel 45 into control systems from other manufacturers. Ethernet and X2X Link are used for the communication system. Full integration of the HMI application into B&R's Automation Studio programming and diagnostics tool goes without saying. The same is true for programming in all of the IEC languages offered by B&R as well as Automation Basic and ANSI C.
Dynamic choreography with forceful precision
"As I mentioned, the control application isn't especially complex, but the system requires a large number of inputs and outputs," says Hofer. "There's an analog input for the auto-lift's height sensor, 10 analog outputs for speed control, more than 40 digital inputs for monitoring the various locking mechanisms, railings and doors and providing external lift control, as well as more than 60 outputs – mainly for controlling the motors and valves responsible for raising, lowering and locking the platform." All in all, the system has more than 70 valves, with each of the elevator platforms (except the auto-lift) featuring a 3-cylinder package at each corner. When all of the podiums are operated at once, 3.5 liters of oil flow through the lines per second. The hydraulic supply lines add up to a total of 1.6 kilometers. The hydraulic station has a 650-liter oil tank and supplies a maximum operating pressure of 250 bar. When the lights come on and an artist or prop emerges theatrically from the depths, only the operator in the control room is fully aware of the dynamically choreographed show being performed with forceful precision in the machine room three stories below. Of the wave of applause that invariably floods through the audience, it is only fitting that a portion always trickles down to the hydraulic actors below.