"Shaft. The Sequel," Input/Output, ME Departments, May 2007

input/output

by Michael Abrams, Contributing Editor

Shaft. The Sequel

Imagine a world where only one car could use the highway at a time, where only a single train could run on a track, and where only a solitary person could stroll down the sidewalk. We'd either never get where we're going or every last piece of land would have to be devoted to roads, rails, and walkways.

Yet, somehow, 150 years after the first passenger elevator started hauling daring riders up and down 488 Broadway, today's lifts continue to operate in exactly this fashion. The current method of shuttling people about—huge banks of building-high shafts, each with a single car—is inefficient, to say the least.

The folks at ThyssenKrupp say they have found a way to fix that. Their new Twin elevator system puts two independently moving cabs in a single shaft—and a working example has already been built in the Main Triangle building in Frankfurt.

That's all well and good for the square-footage-conscious tower owner, the phobic elevator passenger might ruminate, but how on earth do they keep the things from smacking into each other? Such thoughts entered the mind of ThyssenKrupp's head engineer, Karl Schoellkopf, when the project was first introduced to him.

Two cars, one shaft: This simple twist on the old method of vertical transportation may change the guts of every new high-rise.

"At the beginning I did think, ÔOh my goodness, how would it work?' " he said. "But we came very fast to the idea that to make it safe is the only thing. Everything else is very conventional."

Schoellkopf and his team developed a four-level safety system that is new to the world of elevators.

The first innovation can be found at the point of departure: Rather than just push an up or down button, passengers select their destination floor before entering the car. An algorithm assigns the right car to the right floor.

The cars themselves continuously exchange information about speed, direction, and location. If a set minimum distance is not kept, the cars stop at their next landings.

ThyssenKrupp also purchased a separate control system. "Normally, it's used in nuclear power stations and things like that—very high safety level," Schoellkopf said. The system keeps track of the cars' positions by referring to two strips that run along the shaft. One is a magnetic tape and the other a barcode read by optical sensors. If the cars somehow come too close to each other, software is programmed to trigger a brake that will bring both to a halt, even if the building has lost power.

Finally, if some unforeseen calamity should cause even the brakes to malfunction, the same independent software will activate a set of safety gears "for the lower car in the up direction, and for the upper car in the down direction," said Schoellkopf. They push a set of brake pads against the guide rail to bring the car to a stop. "The gears are only activated if all the other things don't work," he added.

Mark Schroeder, ThyssenKrupp's director of new construction sales, pointed out, "Basically, the top car would serve every floor of the building except possibly the bottom floor, and the bottom car would serve every floor except the top floor."

Schoellkopf recommends a three-shaft arrangement with at least one of them being of the conventional sort. A transfer floor might help make the vertical journey as speedy as possible. And there should be two staggered entrance lobbies so that both cars can be boarded at the same time. "It makes no sense to use this system if you have only eight, 12, or 15 floors," he said.

Schoellkopf and his team are now working on an intelligent control system for all the cars in a mixed bank of conventional and Twin elevators. A passenger will push a single button to indicate a destination and will be assigned a specific elevator. If a change is necessary, an indicator in the elevator will identify the transfer floor.

Once you're sticking extra cars in a shaft, why should anyone stop at two? The old paternoster elevators were essentially a chain of cars that circled continuously. For independent cars, however, "there are limitations," Schoellkopf said. "You can use three or four cars, but as long as we talk about elevators that are moved by ropes, it gets more complicated."