Magic moments achieved with safety

An 88 axis machine, accurate to 1mm and resolving to 1 micron, achieves maximum safety in a theatre in Sweden. Developed by the same company that flew dancers around in the acrobatic show in the Millennium Dome, it fulfils the requirements of IEC 61508 Category 4, the highest possible in a programmed environment. Stage Technologies, based in London, is world leader when it comes to moving mechanical contrivances and flying actors on stage. The installation in the City Theatre in Gothenberg, Sweden, uses their portable 'Nomad' PC based terminals to control a system that includes a revolving stage, lifts, bars, curtains, and when required, flying actors. Flying and lifting is achieved through 67 servo driven hoists in the loft. The terminals are called Nomads because they can be plugged in anywhere on an Ethernet network that connects to five S7-300 Siemens plcs that interface with Siemens Simovert Masterdrives via Profibus. The drives, supplied by HMK Technical Services, are suitable for both AC and permanent magnet servo motors, and are connected to each other by a Simolink fibre optic link to ensure synchronisation. Category 3 safety can be achieved by suitable measures inside the drive, but category 4 requires dual redundancy throughout, and contactors on the outside of the drive. In the event of an emergency stop, power is used to decelerate the hoist motors as quickly as possible, after which the pneumatic brakes are applied. At zero speed, contactors then open both inside and outside the drive. In the event of system failure, a single S7-200 plc can be used for manual control of all axes. The Nomad consoles have a simple to understand graphics interface and dead man's handle type bars at wrist positions. Release brings everything to a stop. All programmed sequences can be over ridden using slider bars to stop them, speed them up or slow them down. Safety is paramount in an industry where many of its participants are creative rather than highly technical, and audiences expect thrills without risk. The Millennium Dome show was the first to fly acrobats around in 2D, but the current Chitty Chitty Bang Bang show at the London Palladium requires the car to be flown in 3D. Mishaps in the early stages of the show demonstrated that if anything goes wrong, the system always fails safe, and will in no way permit, 'The show must go on' if there is the slightest element of possible risk. Remembering how factory hoists were at one time regarded as machines to keep well away from when they were working, the ability to work safely in close conjunction with large numbers of them shows how far this kind of automation has come. More than satisfied with its present purchase, the City Theatre in Gothenberg is planning to install another 32 hoists to allow them to achieve even more spectacular effects. Stage Technologies was one of the winners of this year's Queen's Awards for Enterprise in International Trade. Siemens Energy and Automation Stage Technologies HMK Technical Services Pointers System is able to control and co-ordinate 120 motor driven axes to an accuracy of 1mm and a resolution of 1 micron. It is controlled from mobile terminals with graphical user interfaces placed anywhere on an Ethernet network Safety is to IEC 61508 Category 4, the highest possible