Steel
Tuesday | 15 May, 2012 | 9:21 am

Great new heights

By Nick Wright

Mitsubishi Electric’s ultra-high-speed elevators are built for comfort and safety

May 2012 - As skyscrapers around the world are getting taller, the elevators inside them are ascending faster. For visitors and daily office workers making trips up and down, elevator technology needs to keep pace with rising stories—for speed, comfort and safety.

Among the trailblazers in elevator technology is Mitsubishi Electric Corp., Tokyo, which has designed lifts for the 632-meter (2,073 feet) Shanghai Tower currently under construction in China. Three of the tower’s ultra-high-speed elevators will be the world’s fastest when complete in 2014, according to the company. Tawain’s Taipei 101 currently claims the world’s fastest, at 1,010 meters per minute.

Designed to move passengers at more than 1,000 meters per minute, or 60 kph (approximately 37 mph), the three elevators will stop at the same floors. The other elevators, which will be installed in the same building, will stop at different floors, so the length of the shafts will differ, says Satoru Kato, manager of elevator electrical system development at Mitsubishi Electric.

Many basic yet crucial components of any elevator’s mechanics, such as the cables, rails and car frame, are made from steel. Not only is it strong and durable but also its inherent characteristics make steel an ideal vibration absorber.

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Mitsubishi’s sfleX-rope is the centerpiece of its high-rise rope mechanics. The core rope is comprised of bundles of high-intensity steel strands sheathed in plastic, which reduces rope weight.

Each steel wire has a higher density and wider stress area than conventional rope, which helps reduce cable stretch when passengers step onto the elevator. The cars are driven using these ropes by a traction motor, which incorporates a pair of three-phase winding coils and parallel drive systems. Each of the motors, located at the top of the elevator shaft, are integrated with converters to regenerate electricity, dropping power consumption by 30 percent, according to the company.

Finding the balance
For elevators traveling at such high speeds, good vibrations are no vibrations. Three material considerations go into elevator car construction, says Kato. First is the balance between weight reduction and strength, followed by reduction of noise and sound insulation, and improvements in vibration-resistance measures.

The elevator car is made of steel, and the aerodynamic covers on the top and bottom of the cars are constructed from aluminum and carbon fiber-reinforced plastic (CFRP), which is both lightweight and strong. The covers give the car its capsule-like shape and keep it quiet inside. The shape also minimizes fluctuations in air pressure, an imperative for rider comfort.

“We made the elevator ride more comfortable by adopting new streamlined aerodynamic car covers, which reduce wind noise and improve sound insulation,” he says.

Traction machines with low-torque fluctuations smooth out starts and stops, while the active roller guides reduce vibration as the car travels along the steel rails at higher speeds. The traction machine has a permanent magnetic motor for energy efficiency and low noise.

From a material standpoint, finding a balance at high speeds while guaranteeing safety and load resistance presented the biggest engineering obstacles, Kato says.

“We needed to make the ropes and cables lighter in weight but stronger in intensity at the same time,” he says.

Mitsubishi Electric’s two-tiered braking system uses a hydraulic-driven disk brake during regular operation. A governor monitors elevator speed under heavy loads, as well. However, the car will sense and react to an unsafe speed. At that point, a safety gear kicks in. The safety brake shoes are ceramic-coated to resist high heat generated against the steel rails from a quick stop. MM

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