Automation helps Opera Australia’s South Pacific wow audiences
By Harry Mulder, Engineering Manager, Omron Electronics
Monday, 03 September, 2012
South Pacific is undoubtedly one of Rodgers and Hammerstein’s greatest musicals. Set during the Second World War, it deals poignantly with the issue of racism; yet still contains memorable classics like Some Enchanted Evening and I’m Gonna Wash that Man Right outa My Hair.
New York’s Lincoln Center Theatre production of South Pacific premiered in 2008 and received seven Tony awards, including Best Musical Revival, after sell-out seasons on Broadway and London’s West End. This production is currently being performed by Opera Australia, which assembled an all-star cast. It opened at the Sydney Opera House on 8 August and is scheduled to run for four weeks before moving to Melbourne and possibly later onto Brisbane.
As with any stage production, props and decorations form a critical part of creating the overall effect of the show. This is especially true of moving props, like wind-up curtains. Set designer Michael Yeargan uses a series of 15 cleverly slatted screens that can be individually wound up or down as desired. This gives numerous creative effects throughout the show, including a highly effective shimmering effect to create wind. The stage is retractable to enlarge and reduce the size of the stage. It also helps accentuate highlights and diminish the lowlights as it traverses.
The movement of the curtains needs to be tightly controlled so as to work in seamlessly with the production. Servo drives were selected for this, primarily for their accuracy of movement, overall speed and quiet operation. There are fifteen 1.5 kW servos, powered by a single-phase supply. Each incorporates a 17-bit absolute encoder to maintain its homing reference, even when power is removed. A single proximity sensor is fed directly into each servo drive to detect overtravel. All movements are made by a single controller, using a series of absolute commands. The movement of the stage is controlled by a 3 kW variable speed drive.
The slatted curtains are constructed of double-sided, triple-decker plywood. They measure 30 x 12 mm and the width varies from about half a metre to two metres. The height of the stage is about 8. 5 m, but each winding spool is mounted well above the stage ceiling so as to remain unseen. This raises the overall length of the curtains towards 12 m. The larger curtains weigh over 120 kg and with faster movements needing complete wind-up within two seconds, high capacity 40:1 gearboxes are required to carry the load.
The 3-hour production contains some 50 scene changes, each requiring differing positions for all the curtains and the stage. Also, the rate of movement of the curtains varies between scenes, requiring a sophisticated control system to handle both the control aspect and the sequencing. One reason Omron Electronics’ NJ501 machine controller was selected was because of its in-built EtherCAT port that allowed the servos and VSD to be interconnected. Future expansion, although highly unlikely, can easily be accommodated for.
EtherCAT is not only extremely fast, but it also provides the convenience of a daisy chain connection between nodes, thereby shortening the cable run considerably and removing the need for a central switch. It also uses highly economical Cat 5 cable and allows parameters to be set over the network during real-time operation. This is important as serial connections to individual nodes once mounted on stage rigging some 12 m above the stage is impractical.
Considerable finetuning of both curtain and stage positions were carried out during rehearsals. Timing, too, was constantly altered by the production team to achieve the desired effect. This meant that data that could only be practically managed by Excel spreadsheet. Omron’s NS-Runtime allows a PC to act like a standard HMI, meaning the stage manager has a simplified interface for advancing scenes and making online adjustments. However, the in-built recipe handler still allowed tabulated data to be manipulated with each change of scene.
As Cliff Rosell, the Manager of Production, stated, “The system works really well and Opera Australia are very happy.” Even the set designer commented that it was the best system he’d seen in all his international experience. The integration company hopes this success will lead to more usage on additional projects.
The final result was a stunning spectacle, as the author can vouch, having been there on opening night!
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