Theatre automation company Trekwerk has specified around 100 AC drives and servo motors from Control Techniques to automate the movement of back-drops and scenery, and the complex system of lighting arrays, at the Royal Shakespeare Theatre in Stratford-upon-Avon.  Following a four-year £112 million transformation the renovated theatre now has a 1040 seat thrust stage auditorium, with the distance of the furthest seat from the stage being reduced from 27m to just 15m. 

The winch system at the theatre is very advanced for greater flexibility in set design and operation, and safety and reliability is essential. All the winches are fitted with Control Techniques 15kW Unidrive SP AC drives operating in servo mode and twinned with Unimotor 190 fm servo motors fitted with double encoders for precise positioning and speed control.

A total of 46 drives are fitted to 60 winches with at least half of these being positioned above the thrust stage. Any of these can be configured for different duties from lifting of scenery to controlling the ‘flying’ of actors. Sixteen of these winches are positioned in the ‘slot area’ for stage reconfiguring and 14 compact Trekwerk SynchroDisc winches give silent five-line lifting of ‘flybars’ for rapid changeover of scenery during productions. 

Each winch drive is fitted with an SM-Applications Plus module that is programmed to control all of the winch motions, with the load being calculated internally, based on the current being drawn by the motor and checked against a load cell signal for additional safety. Each motor is fitted with both an incremental encoder for speed control and a Sin/Cos absolute encoder for position feedback. All winches are capable of lifting at 2m/s. Sixty of the winches are of a SynchroTwin design which allows one drive to control two 2m circumference winch cable drums either independently or synchronised together. The SynchroDisc theatre winch can be fitted with two identical drums with 6mm steel wire rope, SWR (ie 200kg lift per rope), or one drum with 8mm SWR for lifting up to 24m. With permanent magnet servo motors and high frequency 18kHz switching, no braking noise and damped magnetic braking, the devices are virtually silent.

Thirty light clusters are controlled by 1.5kW Unidrive SP drives and size 115 Unimotor fm servo motors with double-brakes. This facilitates the flying of lights in and out at a speed of 1m/s, using the ‘Light-Lock’ anti-swing device, patented by RSC’s head of lighting, Vince Herbert. The movement of individual lights can be synchronised with the movement of the cluster, each of which has four-cable lifting on two drums.  

All drives that communicate with each other using Control Techniques’ own high-speed network, CT Net, also communicate via CT Net with the Trekwerk control system. Three TNM control desks are pre-programmed with all critical movements for each performance and an over-ride joy-stick control can be used to provide manual speed up/slow down. The TNM control system executes instructions to the drives, with the detailed motor movements being programmed within the SM-Applications Plus module in each drive. All programmed movements can be reviewed in the 3D graphics within the control system.

Control Techniques