Delivery of the drive systems for new “state of the art” stage wagons as part of the recent renovation of the stage machinery at the Stuttgart State Theater.
The installation includes a 12 x 12 meter revolving stage wagon in two parts and two side stage wagons each 4 x 12 meters. Each wagon contains 4 or 8 Visual act drive units, each drive unit capable of moving up to 6000 kg in any direction. The drive units are powered by on board servo amplifiers, controlled by a Visual act wagon controller over an Ethercat network. The system includes a total of 40 motion axes.
Each wagon contains an inductive navigation system capable of following steel guides embedded in the stage floor. The inductive tracks are passive; there are no high frequency cables in the floor as is customary for inductive guided systems. Aside from a friction wheel fitted with an encoder, there is no mechanical interface between the wagon and the floor. The control and navigation systems allow the wagons to move to programmed positions in both x and y directions with an accuracy to better then 2 mm. The accuracy is independent of the load, which can be up to 7 000 kg for the side stage wagons and 15 000 kg for the revolving stage wagon system.
The drive wheels are pressed against floor with the help of pneumatic cylinders. This allows for constant pressure and therefore consistent traction, even when the floor is uneven or when moving over the edges of elevators. The pneumatic system can also be used to raise the drive units from the floor to provide for redundancy in the event of a component failure.
The Visual act wagon controllers operate as slaves to the BoschRexroth axis controllers. The wagons can therefore be controlled from the theaters main control panel and synchronized with other stage equipment.
Safety is an important issue, especially when operating stage elevators supporting the stage wagons. To guarantee that the wagons are properly positioned before elevators move; the inductive sensors are read by both the Visual act and BoschRexroth controllers. In addition, RFID tags embedded in the floor are used to confirm which wagon rests on which elevator.