Located in the heart of Copenhagen, the beautiful ‘Gamle Scene’ – the old stage of The Royal Danish Theatre – was built in 1874 near the site of the original theatre. Last summer, the old stage’s machinery was upgraded and a new control system was installed by Visual Act, an award-winning Swedish stage design and technology specialist. One of the advantages of Visual Act's offer was their ability to extend the lives of the existing dc motors by supplying modern intelligent drives from Sprint Electric. Utilising nearly all of the original motors and maintaining most of the original mechanics, the much needed upgrade could be carried out at a far reduced cost.
In addition to the new control electronics for 36 fly bar hoists driven by the dc motors, the scope of work included the installation of a stage control system with four portable control desks and redundant servers; upgrading six lighting bridges for increased lifting capacity; installation of four new manually moveable point hoists, and a complete upgrade of the old revolving stage – again, driven by dc motors. Visual Act’s design engineer Niklas Philipson takes up the story:
“The refurbishing process at The Royal Danish Theatre in Copenhagen was in many ways special and in some ways unique. We could build on the experience gained in upgrading the flying system at the Norwegian Theatre in Oslo [where Sprint dc drives are also installed]. Often the old dc motors are exchanged for ac motors, but we have good experience in keeping them. It is a cost efficient way, as the dc motor drives have very good capacity and durability.”
To monitor the position of the fly bars, a new arrangement, comprising an angular-geared absolute encoder and limit switch, was mounted on each fly bar winch. Two Profibus communication channels were provided, one for the drives and one for the absolute encoders and safety I/O. The integral software modules of Sprint Electric’s PLX drives were used extensively to facilitate this complex system and a positioning control loop was configured specifically for Visual Act.
The six existing lighting bridges were upgraded to increase their load capacity to 800kg. This involved replacing motors, gearboxes and brakes. New electrical cabinets with servo amplifiers and electronics were also installed. In order to increase safety, slack wire detection was added. Angular gear arrangements similar to those used on the fly bars were also installed for the light bridge encoders.
The revolving stage was inspected and fitted with new encoders and a very old motor was removed in order to improve the efficiency of the installation and to reduce fire risk. The delivery also included four completely new movable point hoists; these have individual control cabinets that are electrically similar to the light bridge control cabinets and are also connected to the control system via the Profibus fieldbus network.
Theatre motion control
The Visual Act control system is being installed in more and more theatres throughout Scandinavia and is fast becoming the new standard in theatre motion control. It is provided with two types of control desk: the Visual Act Advanced Desk, which includes a full keyboard and is ergonomically designed for work over longer periods, and the Touring Desk, which uses a touch screen and is more compact and suitable for operation from a variety of locations. At the Royal Danish Theatre two Touring Desks are rail mounted to one of the galleries.
The control system operates all movements in the theatre through a combined Profibus and Ethernet network, providing communication links to all connected devices. The Ethernet network configuration is a dual-redundant ring, and a number of hot-swap terminal boxes for the control desks are placed at various points within the stage area. To meet the safety standards demanded of modern theatre automation systems, a double emergency stop circuit is connected in series through all the e-stop switches in the system, ensuring the halting of all motion functions on activation.
Sprint Electric’s PLX 4 Q regenerative drives used for the fly bar hoists and the revolving stage are sized between 5kW (12 amps) and 30kW (72 amps). They are all fitted with a Profibus communications module and their compact size ensured easy installation into the specified enclosure system.
PLX is a powerful, flexible and easy-to-programme digital dc drive, offering a broad range of application software functions that enable difficult tasks to be completed easily and efficiently without costly external hardware. Forming part of an integrated range of two- and four-quadrant dc drives, the PLX is highly suitable for retrofitting ageing dc motor control installations with a more cost effective, modern drive system.