The Safety Systems that Support the World’s Fastest Speed Without Worry
The elevators we delivered to Guangzhou CTF Finance Centre, a skyscraper complex in China, were certified by Guinness World Records as “the world’s fastest elevator”*. Running at a rated speed of 1,260 m/min, it takes them around 42 sec to climb 440 m from the ground floor to the hotel lobby on the 95th floor. Safety was the essential element in our achievement of the world’s fastest elevator. Let’s take a look at the safety systems Hitachi developed to help people use the world’s fastest elevator with peace of mind.
* Certified by Guinness World Records on September 10, 2019, as holding the official record title of “The fastest lift (elevator).”
Applying Leading-edge Electronic Safety Technologies to the World’s Fastest Elevator
Developing the world’s fastest elevator requires the technology for not only ultra-high speed movement, but also for stopping the elevator safely. The higher the maximum speed becomes, the more advanced the safety technology must be. So what Hitachi aspired to was the safety to reliably stop the elevator in an emergency situation, to keep users safe. We tackled the development of such safety systems both from the electronic and the mechanical sides.
Yuki Saito of the Control Systems Group, who was involved in the development of electronic safety systems, says “I developed the electronic Emergency Terminal Speed-limiting Device (electronic ETSD). It’s a system that watches the speed and position of the car at the top and bottom ends of the shaft, and makes it decelerate if it exceeds the predefined speed.” Changing from the conventional mechanical type to an electronic type allows more precise monitoring of car position and speed, so warning signs can be spotted before an abnormal situation occurs. Saito says “The advantage of an electronic type of system is that rather than worrying the users with an emergency stop of the elevator, it is possible to take action in advance, by replacing parts, or by stopping at a nearby floor to let people out.”
This electronic ETSD was very advanced technology at the time, and in Japan it had only just been adopted for standard elevators that operate at 105 m/min. Kazuto Naganuma, who worked on product assessment for the Quality Assurance Department, says “Taking what was new technology even within Hitachi and applying it to the speed of 1,260 m/min, more than 10 times faster than the previous speed of 105 m/min, was the most challenging experience of my life in the company.” We developed an encoder able to follow the elevator at ultra-high speeds, and a new microcomputer able to compute the position and speed of the elevator from moment to moment from the signal of that encoder. That established a system able to handle as much as 1,260 m/min.
Reviewing Everything, Starting from the Materials, to Stop Safely from the World’s Fastest Elevator Speeds
We also reviewed all mechanical safety systems for use at 1,260 m/min. First, there is the governor, which detects abnormal elevator acceleration and applies the brake. The descent speed for this elevator is set at 600 m/min for descent, half the ascent speed, out of consideration of the speed that humans can withstand. That required ingenuity to make the same unit detect different speeds for ascent and descent. We placed speed detectors at two locations, on the front and back of the governor. Yosuke Kubo of the Mechanical Device Development Group, who worked on governor development, says “The governor causes physical collision when it applies the brakes, but in this case, three or more times the conventional amount of collision energy is generated, so we researched materials that are strong against impact and abrasion, and tried a variety of patterns. Finding the ideal materials was the hardest part.”
Yushi Sakai of the Mechanical Device Development Group, who worked on developing the emergency stop system which stops the elevator if the rope breaks, says “Reliably stopping a car that goes 1,260 m/min generates around 4.8 times more braking energy than in conventional elevators. The wedge of the emergency stop system that comes into contact with the guide rail reaches 1,000°C, so conventional iron wedges would melt immediately. Therefore, we started from selecting the materials, and developed laminated ceramic braking material.” Also, for the oil buffer which softens the impact force on the elevator car while stopping it even if it hits the bottom of the shaft, we developed four-stage telescopic oil buffers, so we could successfully shorten the pit size by about 9 m. That helped to relieve the burden of the construction works.
The World’s Fastest Speed was Made Possible by Exhaustive Observation and Validation
Elevators must undergo various assessment tests in order to get certified by an official Chinese elevator authorization agency. Because the electronic ETSD incorporates software, the development process became subject to certification, not just the end product. Saito says “Everything was subject to certification, even how the software was tested and what kind of development environment it was coded in, and we struggled to comply with that.” The governor and the emergency stop system received on-site braking testing, in addition to the assessment testing at Hitachi’s G1TOWER, a 213m elevator research tower in Japan. Sakai says “Braking testing of the emergency stop system is a requirement in China. Testing is performed on the elevator that is actually delivered, so we had to make thorough preparations and ensure the safety of the workers while bringing the elevator to an emergency stop from ultra-high speed. After that, we made final adjustments and were able to deliver the elevators with no problems.”
Naganuma, who was involved in the project for over five years, says “The thing that took longest was assessment of the electronic ETSD. Failure is intolerable in safety systems above all, so we took great care over building and assessment at the development stage. Even after we moved to the site, there was a mountain of assessment work to be done on the safety systems, and we cleared the challenges one at a time. That’s why we were so excited when we reached the speed of 1,260 m/min.” “Going to the site over and over again during development is something that normally never happens, so I got a mysterious feeling, as if I was bringing up my own child.” says Kubo, describing his attachment to the project. Saito says “When I was first working on safety system development, I was feeling how tough it was to protect safety, but now I think it’s only natural for an elevator that is a Hitachi product that carries people. We imagine what would happen if each and every component failed, and confirm that the elevator would still be safe in that case, and only then we are ready to ship.” The world’s fastest elevator was made possible by exhaustive observation and validation.