Mitsubishi Electric's speedy elevator gives Shanghai Tower a lift

Mitsubishi Electric's Masaji Iida, far left, Satoru Kato, center, and Yoichi Sakuma

INAZAWA, Japan -- Three ultrahigh-speed elevators are ready for liftoff in the Shanghai Tower, China's tallest building. The state-of-the-art elevators, which travel at 1,080 meters per minute, are a product of the uncompromising Japanese engineers at Mitsubishi Electric's Inazawa Works in central Japan.

     As of last year, the elevators were the world's fastest, 50% faster than those in the Landmark Tower in Yokohama, south of Tokyo. Those elevators, also built by Mitsubishi Electric, were installed in 1993 and were the fastest in their day.

     After it got the order for the Shanghai Tower elevators in June 2011, Mitsubishi Electric set up a project team comprising some 40 engineers to develop the world's fastest lift. The team is led by Satoru Kato, who has been developing high-speed elevators since he joined the company in 1992. He participated in the Landmark Tower project.

     Around 2008, when talks got underway for the Shanghai project, Kato was working on an actuator system that would make elevators faster. He worked day and night, and achieved higher speeds by combining a large-capacity motor and two large-capacity control systems.

Smooth ride

But problems remained. The faster the elevator moved, the greater the vibration. An elevator is made up of the car, a surrounding frame, and vibration-dampening rubber between the two. When two adjacent cars' counterweights passed each other in opposite directions at the maximum speed of 1,080 meters per minute, or a relative velocity of 2,160 meters per minute, the resulting wind pressure caused the rubber to warp, rattling the car.

     To smooth out the ride, Yoichi Sakuma, who was in charge of the team's mechanical development, began trying to improve the elevator's vibration-control system, called the active roller guide. Sakuma attached additional accelerometers at the top and bottom of the car, as well as on the top of the car frame, in addition to the one already placed under the car frame. This made it possible to detect vibration more precisely -- and counter it more effectively -- by generating damping movements in the opposite direction using actuators mounted on rollers running along rails in the shaft.

     Another problem was noise. If the same cars used in the Landmark Tower were used in the Shanghai Tower, they would be as loud inside as a vacuum cleaner. Making the car's walls thicker was not an option because that would add too much weight.

     Instead, Masaji Iida, the design chief, focused on determining where the noise was coming from. By streamlining the air rectification covers above and below the car like the nose of a Shinkansen bullet train, Iida's design deflected the airflow around the car, reducing wind noise. But an experiment showed the culprit was not the air hitting the car itself, but rather the devices outside the cover, such as the roller guides. By tweaking the design to bring these devices under the cover, the noise was cut by 60%.

     Yet another problem was the misalignment between the floor of the car and the floors of the building. The team solved this problem by repeatedly adjusting the controller.