The Bregenz Festival on Lake Constance in Germany provided an enthralling stage spectacle of Verdi’s Rigoletto in 2019, proving that audiences still love great opera, even in the 21st century; and the upcoming season is almost completely sold out, exceeding all past performances in terms of aesthetics as well as technical feasibility. An oversized clown figure functions as the stage. To handle its complex movements, the Bregenz Festival depends on control technology from Beckhoff.
In the production, the court jester Rigoletto becomes a clown. Only the head, encircled by a wide collar, and the hands of the gigantic clown protrude from the lake. Eventually the clown becomes the victim of intrigues. The stage comes apart, the collar sections drift apart and the eyes and nose fall out of the head. Instead of the smiling clown face, a gruesome skull now dominates the scenery.
Demanding motion control
With a diameter of 22 m and a total area of 338 m2, the collar forms the central stage area. It consists of one fixed and three movable parts, which run on a system of rails driven by electric cable winches when the stage breaks apart.
Five hydraulic cylinders and 14 electric motors alone handle the various movements of the head, which is 13,5 m tall and weighs 35 tons. Mounted on a rotating see-saw that is 35 m long, the head can be moved across the stage with a 94° angle. Driven by a central hydraulic cylinder, the see-saw also makes it possible to raise the head or submerge it in Lake Constance until the water reaches its upper lip. “This is no easy feat,” says the stage technology manager. “Moving the head in only 27 seconds from 14,5° degrees above the horizon to 28° below the horizon requires an hydraulic pressure of up to 160 bar.” Nodding motions are executed with two hydraulic cylinders moving at 4.4° per second. And opening the lower jaw takes another two hydraulic cylinders moving at a speed of 10° per second. Four electric motors shake the head and eight more roll its eyes and open and close its eyelids. That means 19 axes for the head alone must be controlled. The power ratings range from 2 to 22 kilowatts for the electric drives and from 75 to 90 kilowatts for the hydraulic pumps.”
The left hand, which reaches 11,5 m out of the water and takes on various functions in the production, has a total of eight hydraulically driven axes. The biggest drive rotates the hand, while smaller drives connected in parallel tilt the hand. Small motors control the movements of the individual finger joints.
“In terms of control technology, the challenge involved making the stage manageable because it was divided into so many individual moving parts. Each individual machine is equipped by its manufacturer with a simple commissioning controller. To communicate seamlessly with the higher level Unican controller, a CAN-bus interface had been specified,” says Wolfgang Urstadt, technical director of the Bregenz Festival.
Redundant axis computers control a total of 29 axes. Two control consoles are used to program and trigger the motion commands. From here, the axis movements are calculated and the commands issued to the underlying Beckhoff controller.
Decentralised control architecture
The great advantage of the Beckhoff control system lies in its diversity of interfaces and its ability to operate with a decentralised control architecture. The cramped space on the floating stage does not have room for a large control cabinet of the type usually found in opera houses. The main cabinet is linked to one cabinet for controlling the collar and a second one for controlling the head.
The control platform in the main cabinet is a CX5120 Embedded PC in combination with a 38 cm CP6602 built-in Panel PC. The control functions are executed with TwinCAT 3 automation software. The algorithms for the precise control and positioning of the hydraulic axes come from the TwinCAT Hydraulic Positioning software library. The fast communication system is EtherCAT, which stands out with its excellent diagnostic capabilities and easy configurability.
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