Machine Design

Who let the grass out?

The retractable roof of the National Football League's Arizona Cardinals new arena in Glendale, Ariz., can be closed to air condition the facility or opened in cooler weather.

The roof panels, made of a PTFE (polytetrafluoroethylene) coated fiberglass fabric, are much lighter than a traditional clad roof. But the roof isn't the only thing that comes and goes.

The natural-grass playing surface sits in a 16.9 million-lb tray that is 234 400 ft, the first of its kind in North America. The roll-out field should save an estimated $50 million as it is cheaper to move the field outside than retract the entire roof to let the sunshine in.

The stadium-mechanization designer Uni-Systems, Minneapolis, partnered with ABB Inc., New Berlin, Wis., using ABB ACS800 Direct Torque Control drives to open and close the giant stadiumroof panels. Uni-Systems' resume also includes work on Minute Maid Park and Reliant Stadium, Houston, Tex.; Miller Park, Milwaukee; and RFK Stadium, Washington, D.C.

ABB Inc.,
(800) 752-0696,

(763) 536-1407,

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