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Motion control, theme park style

The game and ride controls also mount a coordinated response to back-ups or delays, which could be caused by someone triggering one of the attraction’s many pressure-based safety devices or even a slowdown in the vehicle loading process. “We know back-ups happen,” Gerstner says, “but system does the right things even when everything isn’t perfect.” Those right things include launching game sequences, such as an extra practice round if users get stuck in front of one screen for too long. They also include more theatrical responses, such as an announcement voiced by “Toy Story” characters.

Many of these coordinated efforts require the ride and game controls to use position data gathered by two complementary tracking methods. The first uses Pepperl+ Fuchs binary proximity sensors, four of which are mounted beneath each ride vehicle, to pick up a set of absolute position markers scattered at strategic locations along the track. “These give us an indication of where each vehicle is in the building,” Gerstner says.

While crucial for generating the go-no go signals and controlling the flow of multiple vehicles, proximity sensor tracking lacked the resolution needed to register the vehicle to the game screen. So the Imagineers added a second tracking system that can determine vehicle position within an inch. It uses a Banner laser sensor, again under-mounted on the vehicle, to read graduated strips placed in the floor near the parking locations for each game. This fine-positioning system helps compensates for all the variation inherent in the mechanical system. “The game doesn’t care if the car parks in the same spot every time. It just needs to know where each car has actually parked, and it can compensate.” Gerstner says.

Positioning data also plays a key role in determining the position of the shooter relative to the game. An algorithm in the game software determines position using data from the three encoders on the shooter itself along with another encoder that measures the amount of swivel on the ride vehicle turrets. “Turret swivel is superimposed on the rotational axis of the shooter,” Gerstner says. The shooter-position algorithm also takes the vehicle’s actual parking position into account. Gerstner describes this positioning algorithm “very complex,” but adds that it still made more sense than trying to come up with a separate sensing system. “We had enough accuracy to mathematically determine the position of the shooter tip with data we already had,” he says.

A new approach

Midway Mania’s controls embody a couple of important departures from Disney’s traditional way of engineering large control systems. Gerstner points out that the company’s larger attractions tended to have point-to-point I/O in the past. That design approach can be clearly seen in square footage set aside for I/O cabinets in a room adjacent to Midway Mania’s massive computer farm.

Much of that control room remains empty, however, since the ride controls take up just two cabinets. Gerstner attributes much of the control system’s physical economy to the Siemens’ distributed I/O and to the Ethernet backbone that ties all the control systems together. “Ethernet simplified the wiring and all the associated touch labour,” he says. “To be honest, I don’t know if we could have done this project using our traditional architecture. It would have taken a lot of copper.”

Another departure for Disney is in its use of a centralised controller in an attraction of this scale. In previous rides with a similar zoned busbars — such as its Rocket Rod ride — Disney had to distribute the controllers around the rides. “We couldn’t go centralised because of the challenge of processing and send permissible signal out to all the zones,” Gerstner says. The 319 had speed and power to overcome that problem. “It’s a screamer,” Gerstner says.

In fact, central PLC and the ProfiNet RT had more than enough processing muscle and speed for this application. Scheel notes that the central PLC scans and execute the code for all 397 busbar zones in 32 milliseconds. “We could go faster if we had to, but there was no need,” he says, noting that ProfiNet RT can update every millisecond if necessary.

Same goes for PCs and Ethernet used in the gaming systems. Gerstner says it has bandwidth to spare, and its switches only utilise about 10 percent of their capacity at any given time. “That’s the thing about bandwidth, you never know how much you’ll need when you start a project. So it’s always better to have more than less,” he says.

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