Chitty Chitty Bang Bang

Stages of automation

The next time you visit the theatre, the scenery and performers you see flying from wing to wing may be under the control of a technology that started life a few years ago in the manufacturing and process industries. E&T raises the curtain on theatrical automation.

Peter Pan is propelled by Profinet. This technology, which wows the crowds by making theatre performers soar across the stage, is the open Industrial Ethernet standard for distributed automation systems, developed by Siemens and the Profibus User Organisation.

Using existing IT standards such as TCP/IP, XML and OPC, and built on the IEEE 802.3 collection of wired Ethernet standards, it enables the integration (via a proxy) of existing fieldbus systems such as Profibus, DeviceNet, and Interbus, without the need to change existing devices.

It is also scalable and offers three performance protocols - TCP/IP, for non real-time applications; Real Time (RT), for real-time transfer of time-critical process data; and Isochronous Real Time (IRT), for motion control applications. It is this last one that is now being adopted in the world of entertainment, whether it be big West End productions, opera houses, touring plays, concerts, or even TV and film.

Profinet IRT was developed principally for high-performance motion control systems requiring sub-microsecond synchronisation, a 1ms cycle time, 1µs jitter accuracy and guaranteed determinism. Since software introduces jitter above 1µs, Profinet IRT is a hardware solution with highly synchronised Ethernet nodes. Each Profinet IRT device has an ASIC chip for handling node synchronisation and cycle subdivision, and incorporates an intelligent two- or four-port switch, so extra switches are not needed.

Using full-duplex switched Fast Ethernet, Profinet IRT divides the communication cycle into a standard TCP/IP open channel and a deterministic RT channel. The channel ratio is system-dependent but is typically 50:50. In addition, there is a 'lane' reserved for IRT to guarantee a real-time response regardless of level of network traffic and to give unlimited access to TCP/IP, IT and other services.

All this may seem a world away from greasepaint and grand opera, but as performance innovators such as impresario Cameron Mackintosh and the Cirque du Soleil company continue to push the limits of what can be achieved on stage, the technology has been developed to meet it.

Profinet: theatre of accuracy

Profinet, and its IRT variant, represent the latest stages in evolution in theatre automation, providing capabilities beyond those of Profibus and Simolink (see table), a proprietary network for motion control developed by Siemens.

As Dr James Pearce, technical manager at equipment supplier HMK Technical Services, explains: "Profinet gives a more consistent response and better synchronisation. For example, you could have a piece of scenery operated by two winches but if, when you want to lift it, the winches were slightly out of step, you'd notice it and that would spoil the effect - rather like in printing, when the colours on a page are out of registration.

"Another important factor is responsiveness. The guy at the control desk could have personal control of 200 axes or more, which in a factory would be spread over different machines, so when he needs something like a piece of scenery to stop, it has to stop. Or he might be controlling the speed override of a move so that a piece of scenery works in time with the actors.

"These are examples of what we can do better now than before," he says, "although we're at a phase now where Profinet gives us a platform to do new things. Profinet allows high bandwidth, 100Mbit/s, while maintaining synchronisation, and is the next level of integration of what were formerly dual networks - Ethernet and Profibus. We could never have used Profibus for a complete network, as the bandwidth is just not high enough."

Nor would Profibus have allowed the kind of wire-based acrobatics from performers with the likes of Cirque du Soleil, whose automated 2D and 3D flights across stage would not have been as easy to execute - and, more important, using the same network - without Profinet, which allows the control desk to calculate the path of motion in proprietary software then send it as a 'map' to the motion controllers, to be processed as a content addressable memory table.

Greater flexibility

Profinet also offers greater flexibility in the theatre than Profibus, Dr Pearce says: "In the theatre, you don't necessarily know which axes follow which. For example, on one day control axis 1 could be coupled with axis 80; the next day it could be coupled with axis 20. Perform-ances change, especially in touring productions, and even within a single show you may have to synchronise different axes.

"Industrial process are usually fixed, but that's not the case in theatres, and Profibus has never really had the required flexibility.

"It's rather like treating the axes like actors - they have to be 'multi-talented' - so with scenery you want it to do different things at different times," says Dr Pearce. "And while the automation equipment is very predictable, the guy at the control desk needs to have dynamic control to fit in with the actors, who are not always predictable. "One thing you don't want scenery to do though is sway, and we're developing the ability to stop this." In essence, this feature, which is still under development, allows for compensation for the effects of gravity, using motion controllers running anti-sway software originally developed for large cranes."

Profinet-based systems also take less time to commission, says Dr Pearce, because there's only one network to configure. And Ethernet, unlike Simolink for example, tolerates breaks in the drives network - a rough comparison here is in the difference between old Christmas lights, where if one lightbulb wasn't working the whole set wouldn't work, and newer sets where it's possible to see at a glance which bulbs have blown.

This may seem a frivolous (albeit topical) comparison but it has valuable ramifications for these systems, in terms of remote diagnostics and reprogramming of drives. If, for example, a drive needs to be replaced - which can be carried out during a performance if necessary - it can be reprogrammed with the original drive's parameters directly from the control desk.

And because Profinet supports TCP/IP, diagnostics can be carried out from anywhere in the world over the Internet, using little more than a conventional Web browser such as Internet Explorer. At a local level, this TCP/IP support also confers automatic routing and re-routing, as happens when we log on to the Internet ourselves.

Real-time dynamic tracking for lights

For the future, the capabilities of these systems will only grow, and the effects become more sophisticated - in fact, they will have to. As Mark Ager, managing director of entertainment engineering company Stage Technologies, explains: "Increasingly, the theatre is competing with films and video games for that 'wow' factor, so the effects we're called on to help produce are becoming ever more complex.

"For example, until recently, most actions were simple up and down, from one point to another; now they're more complex and in 3D. We're also being called on to provide greater integration with lighting systems, to allow moving lights to track moving scenery or performers automatically."

In this application, real-time data feedback is used to follow something on stage, allowing tracking with pan and tilt as well as maintaining constant size of the light beam. Changes of speed or path, as well as preset dark regions, can also be handled dynamically, and tracking continues even if the lighting fixtures themselves are moving simultaneously.

"We're also developing greater interaction on stage," says Ager. "For example, we've been involved in a show in the US called 'Ka', by Cirque du Soleil, which has a vertical wall, down which the performers abseil to the bottom, and when they reach the ground they hit a touch-sensitive platform that sends out ripples of light."

But theatres, and theatre directors, are not interested in all this underlying technology - they simply want to tell the system to move this piece of scenery or create that lighting effect, and expect it to do it. So the control desks in such systems usually come with a standard Windows-based GUI, although incorporating theatrical terms such as 'Deads' and 'Flip' in the command menus - a Dead is a null point in the range of travel of a piece of scenery or lighting bar; a Flip is a matched pair of command sequences, usually for two sets of lighting, that work in opposition to each other.

Lighting design at Chapter, Cardiff

These are still sophisticated systems, however, with a range of features that can trap the unwary or impatient. Dan Young is the technical manager at the Chapter theatre in Cardiff, a 'black box' venue that specialises in experimental theatre and dance but which also puts on a wide range of performances from local amateur dramatics to opera and rock and pop concerts. He does a lot of lighting design work for incoming companies and uses one of the best known modern control consoles in the industry, Acrobat.

He recalls: "The first time I hired one of these desks, it was three days before I had to use it for a performance. I could have taken the tutorial for it but chose to learn for myself, and it took me the whole three days to get the hang of it - it was a very steep learning curve, and I'm still learning.

"I think it's changed my job in two ways. On the one hand it's made it easier; for children's shows, for example, where the sheer range of options allows me to use say only five lights instead of 25 to achieve a desired effect.

"But having these options, and the ability to change things more readily, can also make life harder and lead to a complexity in the lighting design that doesn't necessarily add anything to the show. For a 'proper' performance, so to speak, you need to avoid going overboard with the effects, otherwise it can end up looking gaudy, like a TV game show. Having all these options doesn't mean you have to use them, and you have to be careful not to create distractions from the dramatic impact," he says.

"You need to be sure about why you're using particular functions of the system, and justify your use of them."

It's not often one can use the terms 'process industry' and 'theatre production' in the same sentence, but as you enjoy the season's finest you might want to give your own round of applause, perhaps even an encore, to the people who took Profinet off the factory floor and put it on the stage.

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