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ThyssenKrupp, a German firm perhaps best known for its steelmaking, has developed the world’s first rope-less elevator system. Much like the famous glass elevator in Roald Dahl’s Charlie and the Chocolate Factory, it can not only travel up and down but horizontally too.
Without the need for restrictive and heavy cables, the elevator is able to travel higher and on more complex routes, with multiple cabins operating independently in a continual loop operation.
Just a year on from the conception of the Multi system, ThyssenKrupp has demonstrated it with a 1:3 scale model, which has two 10m shafts and four cabs.
Instead of ropes, the system uses linear motors, which enable the horizontal movement and transform traditional floor-to-floor elevators into what the company describes as a “vertical metro system”. The cabs run on rails to which they are held by the magnetic levitation technology that the company uses in its Maglev trains.
Seen as a much-needed solution for super-tall buildings, the technology increases transport capacity and efficiency while reducing the elevator footprint and peak loads from the power supply.
Andreas Schierenbeck, chairman and chief executive of ThyssenKrupp Elevator, explains that there has been a boom in super-high-rise buildings of 1,000m or more, but traditional elevators have not been developing quickly enough to meet the needs of the construction industry. “The elevator industry is actually limiting the construction of super-high-rise buildings,” he says. “This is because there is only one cabin per elevator shaft but you have to guarantee the capacity of the elevator to suit the need of the building.
“If you build too high you need a lot of shafts, which reduces the amount of floor space you can utilise later on. A traditional rope system can go up to anywhere between 600m and 650m and this sets the limit for a lot of construction projects.”
To overcome these limitations, ThyssenKrupp engineers were set the task of finding a solution. The “ultimate design” was an elevator without ropes that can go as high as it needs to using linear motors, with multiple cabins per shaft to increase the capacity as and when it is needed.
Technology challenges
Schierenbeck says: “We already have a system with two cabins per shaft which has been running for 12 years so we know how this works. The next step was to see if we could construct the Multi elevator system which would solve most of the problems that we have in the industry.”
Markus Jetter, head of development at ThyssenKrupp’s centre in Neuhausen, Germany, explains that to create such a system meant tackling four major “pillars” of technology. The first was the linear drive, a technology the company knows a lot about. Jetter says: “It is a very mature technology. We use it for our Transrapid Maglev system, our magnetic levitation train that runs in China.”
Using linear drives enables the cabins to move in shafts in the same way that trains move, with multiple cabins per shaft, and allows vertical as well as horizontal movements. A benefit is that this means that only the sections of the shaft where the cabs are located can be activated. The active part is on the shaft side and the passive on the cab side so that energy consumption is only active when cabs are accelerated and decelerated.
Cutting weight
The second pillar that the engineers had to consider was materials. Jetter explains that with linear technology there is the need for lightweight cab design, instead of the heavy steel that is traditionally used.
Schierenbeck says this was no easy task. He explains: “With a traditional elevator you have a central engine and motor and a cabin which can weigh as much as it wants, since you have a counterweight over a rope. Therefore more weight is better for the friction of the drive systems. With the Multi, our engineers had to think completely differently.
“They had no central engine, there is an engine over the whole scale of the shaft. The cabin must be lightweight because weight is not your friend any more – it makes it more difficult. We had to re-engineer everything and, really, re-engineer our knowledge.”
Jetter says the company’s technology centre develops carbon composites. He adds: “It is not only about new materials but also how to use them in a mixture.” Taking inspiration from the automotive industry and Formula One materials, the engineers settled on a combination of carbon composites and the latest in lightweight steels, such as hot-stamped steel, to reduce cabin weight by 50%, reaching 800kg, which Jetter says is ideal.
The third pillar to tackle was fail-safe operation. This has seen ThyssenKrupp develop a very high redundancy and diverse system to check positions, speed, direction and distances between cabs, as well as safe communication between the cabs. Engineers have also ensured a way to give safe commands to the linear drives to slow down or change traffic patterns.
Jetter says: “This is achieved through a whole network of sensors with safety computers checking and evaluating them all. Also safe actuators are there to detect a failure and ensure safe function.”
As the company has already operated an elevator with two cabins running independently in one shaft for 12 years, Jetter says he is confident in the fail-safe systems that will be applied to the Multi design.
The fourth and final pillar was to develop a new kind of elevator technology, dubbed the exchanger. Operating on the premise of a circular system, such as a paternoster, the Multi will use a single loop that can incorporate various cabins. To achieve this, the exchanger will turn the ‘backpack’ of the elevator 90°, allowing horizontal movement. With a targeted speed of 5m/s, the system will enable near-constant access to a cabin every 15 to 30 seconds, with a transfer stop every 50m. Jetter says: “That is what our customers want: to have small waiting times and shorter times to destination.”
The Multi system uses a similar amount of energy as a traditional elevator. Jetter says that elevators use just one digit of a percentage in the energy demand of a building. However, more and more building owners are looking for zero, or even minus, energy solutions such as generating renewable energy.
He adds: “This means that energy consumption is very important. Our conventional elevators are a high burden to so-called smart buildings with their high masses, which can easily be 10, 20 or even 30 tonnes, when they accelerate and decelerate. During those two phases there are very high peaks of energy demand or high currents when it feeds back. While feedback is a good thing, such a high peak is difficult to handle and it can be wasted.”
Saving energy
Jetter explains that ThyssenKrupp is looking for smart grid solutions and believes that Multi can be a great contributor as it will avoid those large peaks because it has a much lower moving mass.
The fact that the Multi can scale its capacity to demand means that people can be transported more efficiently, saving power for when it is truly needed. Schierenbeck explains: “Traditional elevators are defined by the capacity needed. If you need a cab to go from station A to B you will need a 60ft bus for the maximum amount of people it will need to carry. This bus may never be full in the day, perhaps just once in the morning. With the Multi you don’t have a bus any more, you have 40 or 50 cabs and you are only using the number you need. So if two people are there you take just one small cab.”
Installation of the system is also more efficient than with traditional methods. Typically, when installing an elevator for a 500m building the shaft must be ready and empty to build the machine on the top, which can only be done when the building is finished. Then you must install guide rails and 500m long or double-length 1,000m long cables. This is labour intensive and time consuming.
Schierenbeck says that with the Multi installation can start on sections during the construction of the building. The engineers hope to create a smart modular approach to installation and be able to “grow with the building”.
Without bulky cables, the Multi can also reduce maintenance issues. Typically, repairs would require taking an elevator out of service. However, with multiple cabins, you can simply take one out to do maintenance or replace it completely. Schierenbeck says: “Most of the time we don’t have to put an elevator out of service to carry out maintenance.”
This will all be proven when ThyssenKrupp tests its Multi system. Jetter says: “This will be quite a tough procedure but we now have the ideal test environment – our test tower in Rottweil, which has already topped out at 244m. This year we will start to install and test.”
He adds: “Although we will keep a conventional design for low-rise elevators, ropes are just limiting us in super-tall buildings. While we are aware that heavier and stiffer ropes can be used, if you look at buildings like the World Trade Centre they have a very low frequency of building sway and this is a problem for ropes. The only solution if we want to go higher is to avoid ropes and this is the best aspect of Multi.”