With a height of 442 m (527 m total height including antenna), Willis Tower in Chicago, also known as Sears Tower, used to be the highest building in the world. Since it lost this status to the Petronas Towers in Kuala Lumpur in 1998, the Willis Tower has raised attention with a new attraction: Modeled after The Grand Canyon Skywalk, the Sky Deck was created on the 103rd floor. These three glass balconies are mounted to the facade on one side only. They allow visitors to stand on an almost free floating glass floor 412 m above the ground. The observation deck of the World Trade Centre's south tower was located at 420 m. Since it's collapse in 2001, the Willis Tower offer the highest lookout point in the USA.
Each of the glass encased platforms can be moved in and out of the building's front like a box for cleaning and maintenance purposes. In the outer-most position, RACO electric cylinders operate the locking bolts and thus guarantee safety. In order to ensure a safe operation, the actuators have an integrated position control and automatic overload switch-off. These features as well as the signaling of the end position and the submission of the general operating status are realized by RACO sensor technology type EPS06. In case of disturbances like power failure, the lock can be released manually with a handwheel at the motor.
It is possible to control the three-phase motor according to its speed with a frequency converter that was integrated into the building's automation technology. Because the electric cylinder is controlled in intermittent duty and therefore does not need energy in stand by mode, the system is very energy efficient and environmentally friendly.