Drives star at the refitted Royal Opera House

At the Royal Opera house, the majority of the motion, to move backdrops, light bridges, scenery wagons, and even the Proscenium Arch, is provided by 316 Unidrive and Dinverter AC drives

The Royal Opera house is a showcase of all that's best in classical and modern cultural entertainment.

Behind its glittering facade it is also a showcase for something else - automation.

Following the recent £214m refit, the backstage area of the ROH has become a panorama of movement to enable scene changing in as little as 21/2 hours.

The majority of the motion, to move backdrops, light bridges, scenery wagons, and even the Proscenium Arch, is provided by AC drives: 316 Unidrives and Dinverters, from Control Techniques, the preferred supplier for the project.

The Royal Opera House is known the world over for opera.

However, its name does tend to obscure the fact that the House is actually a repertory theatre.

At any one time as many as seven separate shows can be in various stages of production in the building.

With repertory the accent is very much on getting scenery changed quickly to allow the maximum time for rehearsals.

The tight schedules mean that it is imperative that everything must run smoothly and reliably.

Equipment failures in particular must be avoided; as these can lead to lost performances, which are costly, and a blow both to the prestige and reputation of the House.

The importance attached to the requirement to change stage sets quickly can be judged from the fact that, out of a total refurbishment budget of ?214m, over 10% was allocated to automation and motion systems, in the form of the overall Nomad 3d Control System, "quiet" AC drives and electric motors, hoists, a long travel gantry crane and associated mechanical equipment such as gearboxes and hydraulic systems.

With so many different areas to concentrate upon, and with many specialist theatre contracting companies involved in the project, one of the main objectives for the ROH engineers was to ensure conformity in the products employed in the automation systems.

This was important because once the contractors had "passed off" their various areas as complete the House engineers would assume authority, and the last situation that they wished to face was a profusion of equipment from different manufacturers.

Because of their potential for complexity, this was particularly true of the drive systems to be employed.

In fact AC drives quickly became one of the main focus areas for standardisation due to the large numbers called for in the project specification and their use in all areas of the theatre.

In any project there are certain factors that are instrumental in determining which supplier will be awarded a contract.

In the case of the drive systems for the ROH there were two: Control Techniques reputation for successful projects in the theatre industry, especially with its unique 3 in 1 Unidrive, product, and the up-to-the-minute advice the company were able to give to the ROH engineers on the subject of harmonics.

The ROH is right in the heart of London and there were concerns that, with up to 40 drives operating at one time, harmonic distortion could be a problem for surrounding enterprises.

Control Techniques development engineers have made an in-depth study of the problems of harmonics and were able to recommend active harmonic filtering on the mains supply to comply with the latest G5 legislation.

A number of major contractors were involved in refurbishment project.

Control Techniques worked in close conjunction with three in particular: KRUPP in conjunction with UK based STAGE TECHNOLOGIES (through Control Techniques German Drive Centre) on hoist systems, Telestage Associates on the Proscenium Arch, the Proscenium lighting bridge and various elevators, and Clarke Chapman on the movable scenery wagons which make up the stage area.

Viewing from the auditorium of the ROH towards the stage the first thing one notices is that the stage is framed with an arch.

This is known as the Proscenium Arch and is the portal through which the audience view the performance.

In the ROH the arch is movable to suit the demands of different productions: in effect a picture frame that goes up and down, in and out.

The precise movement of the arch is the work of Telestage Associates, one of Britain's leading manufacturers of stage rigging and machinery.

Telestage's participation in the ROH project offered the advantage that the company was already standardised on Control Techniques drives.

"The multi-functionality of the Unidrive, with its integrated PWM, Flux Vector and Servo operation enables us to use just one drive across most of our applications", explains Paul Clarke of Telestage.

To control the Proscenium Arch Telestage used Unidrives in flux vector mode in a system with four digitally locked motors to achieve the degree of synchronisation required.

A similar system, but with two motors digitally locked, is used on the Proscenium lighting bridge.

All of the Unidrives in both the Arch and lighting bridge systems are equipped with the UD70, 32-bit RISC applications module, and are hooked into Control Techniques high speed Fieldbus system, CT Net.

This provides an interface, at data rates up to 5Mbits/sec, to the main Nomad 3d Motion Control System.

The UD70 units used by Telestage in its areas of involvement are a minute cross section of the total used in the ROH project as a whole.

The importance of the UD70 to achieving success in many sub-projects in all sectors of the House stemmed from its dual roles in simplifying the task of programming and of providing the key integrator element for the newly installed drive systems.

With its 96k of onboard memory and task-based architecture, the UD70 provided the House project engineers with a low cost, "on-drive" facility for writing application specific programs, and also with a means of for achieving real time control at high speed.

The writing of the software for the modules was considerably simplified by Control Techniques', Windows compatible, Drive Programming Language (DPL).

This is a higher level language, custom designed for developing, testing and debugging application specific programs.

The UD70's key integrator role resulted from its high-speed communication capabilities and from the flexibility in the way it can be used.

In the former case, the benefit is that the Unidrives are able to communicate directly with each other, and with the Nomad system, in real time, to ensure the maximum in system response and fast co-ordination of activities.

In the latter case, the fact that the UD70 is an "add-on" to the Unidrive means that it can be fitted at any time.

Consequently, linking the Unidrives from the various sectors of the theatre into the Nomad control system can be a progressive operation.

Telestage's involvement with the ROH project also included a Pallet Hoist, which transports props to a stage workshop.

Situated at the rear of the stage, the Pallet Hoist can carry as much as 9 tonnes when fully loaded.

It moves over a vertical distance of 22 metres and is required to stop within a tolerance band of just one millimetre.

Working to such a tight specification many companies would have plumped for servo control.

However, Telestage have achieved the desired result with a Unidrive operating in closed loop vector control mode.

This solution offers the advantage that it employs a standard AC induction motor, so the cost and complexity of a servomotor is avoided.

Moreover, the induction machine is more suited to the application in view of the power output required to raise and lower the lift.

Under the Proscenium Arch is the central key to the new flexibility that the ROH enjoys in moving scenery fast.

The stage floor is a multitude of 15m x 5m sections, or wagons, each capable of carrying up to 16 tonnes and of being transferred from stage to storage, and visa versa, within the theatre.

The mobile wagons sit on top of a compensating elevator system and carry the stage scenery and sets.

Each one runs on turtle castors and is driven via an extremely cost effective Control Techniques Dinverter, and geared motor combination, driving through a toothed belt system.

Thirty-seven metres above the stage floor are quantities of fixed and point hoists that are also crucial elements in the movable panorama that is the ROH.

The hoists are all linked into the Stage Technologies' Nomad control system via Unidrive LFT drives.

The designation LFT means that the drives are specifically designed for lift operation and to make the minimum of noise during their operation.

This is extremely important because they are called upon to operate actually during performances.

The LFT drives operate at a high motor switching frequency (12kHz) to ensure quiet motor operation.

In many applications the effectiveness of their operation means that motor noise is actually lowered out of the audible range.

The LFT is also fitted with a special low speed fan, which provides adequate cooling, but at the same time ensures a minimum audible noise level (less than 60dBA).

The two major uses for the fixed hoists are raising and lowering theatre backdrops, on what are known as flybars (these can be locked together via the Nomad system), and also to control the positioning of the many lighting towers in the theatre.

The varied nature of the ROH's productions means that there are a staggering number of backdrops to choose from.

They are all stored away conveniently in the roof of the ROH and are inched down when required onto a horizontal, long travel gantry crane that delivers them into the flytower.

The crane is controlled by a Unidrive with an on-board UD70 module.

It is equipped with a joystick control to provide a creep mode of operation.

The joystick also provides an "analogue" method of programming by allowing the crane to be advanced to set positions under manual control.

An encoder on the crane drive motor feeds back positional information to the UD70.

This is logged, or "learned", by the Unidrive, enabling the same positions to be achieved under fully automatic control.

In addition to the fixed hoists there is also a quantity of 30-point hoists, arranged in a mechanical matrix.

These provide added flexibility as they can be assigned, via a system of cables and pulleys to whatever operational functions are required.

The final words on the project belong to Jeff Phillips, Project Manager at the House.

"The reopening of the Royal Opera House, on December 1st 1999, after being closed for nearly 21/2 years, was the culmination of a project that moved the House into the first division of theatre automation in the 21st century.

The achievement of the ROH project engineers and contractors, with technical support from suppliers such as Control Techniques, in integrating so many aspects of theatre technology under the auspices of a single control system is a considerable one.

True, there are still some areas where we are using a mainly manual control, but it is only a matter of time before these are integrated into our Nomad control system, to provide us with even greater flexibility in our future productions".

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