High-Speed Elevators

DateMarch-February 2019 by Erol Akçay Liftinstituut Solutions B.V Technical Maneger - Eurasia Print

Today, the number of buildings is increasing depending on the increase in the population and thus, the need for vertical transportation also rises. Higher and higher buildings create the need for meeting the demand for vertical transportation more rapidly. In parallel, the speed of the elevators also becomes higher. Then, what is the difference between high-speed elevators and low-speed lifts?

Before we can answer that, we need to address the question of how much is the speed of the high-speed elevator? Fundamentally, according to standards and regulations, there is no concept such as a high-speed elevator. Having said that, in the article of the TS EN 81-20 standard, it is indicated that when the speed of an elevator exceeds 3.5 m/s, ropes should be used in the compensation device and they need to include a tension gear. Therefore, elevators over 4 m/s speed are considered high-speed. For the global elevator companies, 4 m/s speeds and above are considered high-speed elevators and they require the application of a different model.

There is no difference between the high-speed and low-speed elevators in terms of the working principle. However, in terms of hardware, the high-speed elevators comprise a larger number of components and, naturally, are heavier. In general, compensation ropes are employed between the counterweight and the car in this type of elevator, as mentioned above. The compensation ropes wind around a group of pulleys at the bottom of the shaft. This device has an important role in the stable travel of the elevator. The compensation device taking place at the bottom of the shaft naturally increases the required depth of the shaft. Therefore, especially when the speed exceeds 2.5 m/s, the shaft bottom requires higher dimension depths. Accordingly, as the speed of the elevator rises, providing the elevator comfort increasingly becomes harder. The air mass that is pushed and drawn within the shaft on the top and the bottom of the elevator disrupts the stable movement of the car and causes higher vibrations, especially horizontally. In order to minimize the vibration, several equipment and methods are employed. One of these is hanging weights on the bottom of the car that help it to remain at the center. The concrete weight of varying kilograms placed after the installation of the cars is completed puts extra stress on the motor; however, they reduce the sway of the car. In addition, car guide rails become more complicated components. The slide-type guid rails quickly become worn, due to the increasing friction as the speed rises and the differentiation of the friction surface area, causing more vibrations both in the vertical and horizontal axis. Therefore, roller guide rails are preferred. This type of skate, which grasps the main rail with 3 or 6 wheels, depending on the design, is equipped with springs that have suitable rigidity in order to absorb the sway. As the speed increases — for example, as the speed goes up to 7m/s — the features of the wheel and the absorbing pieces are improved. The diameters of the wheels go up to 20-30 cm from 10-15 cm and the springs are replaced by rubber-based dampeners customized according to the load and speed of the elevator. The price of these skate sets only goes up to 20,000 USD from 9,000 USD. With the speeds over 10 m/s that we can refer to as ultra-high speed, the producers can even use electric skates equipped with frequency damping electronic components. The air mass moving along with the car also poses an important problem in terms of aerodynamics. Therefore, another design feature is the aerodynamic casing. These casings are basically composed of metal plating mounted to the car, with the purpose of creating a pointed dome on the top and bottom of the car. They are used by the producers, especially for speeds over 6 m/s, in order for the car to slice through the air mass within the shaft. The amount and speed of the moving air also causes an increase in the risk of failure resulting in excessive vibration of the doors and locking mechanisms. For this reason, building air-escape openings with single-direction casings at the top, middle and bottom of the shaft might be necessary. The increasing speeds cause the safety requirements to be increased and the connected safety components to be larger both in terms of dimensions and features. The buffer strokes considerably increasing along with the speed create the need for building deeper shaft bottoms. The elevator producers use deceleration devices to decrease the impact speed of the elevators to prevent excessive stroke increase. These devices signal an electronic mechanism by detecting the position of the elevator while it is near the terminal floors by means of the mechanical contacts generally placed on the rails. The electronic mechanism on the control provides for decreasing the speed of the elevator automatically in any dangerous situation. Another safety installation affected is the car brake and the overspeed regulator. As the car brakes become larger in dimension, the use of tandem (dual) brakes is another application. The speed regulators increase in size and their working principle also changes. Components that provide induction with mechanisms composed of encoder and bobbins are added to the regulators, most of which operate on the principle of inducing a mechanism by being tensed by the centrifugal force of a spring. Motor brakes are larger in dimension and number.

In the same way, the number and quality of the shaft information system components increase. Flag scanners having more scanning members, magnetic or barcode strips scanned by a speedometer across the shaft, improved encoder systems are added to the hardware, and the leveling differences, due to excessive stretching in the rope length and the gaps in the detection of the car position, need to be prevented.

The changes to the motor and the suspension system are lesser, but they require improvements on the hardware. While the motors are strengthened through the application of bigger and more efficient permanent magnet stators, the suspension system goes back to 1:1 type in order to prevent increasing the speed of the motor at ultra-high speeds. Several companies are already experimenting with composite materials, which are lighter but have the same resistance as steel ropes, in order to reduce the weight of the rope.

The control, software and the electric component become more complicated as the speed increases. Inverters adjusting the speed of the elevator by constantly changing the voltage and frequency of the electrical current are equipped with much larger electronic on/off elements, capacities, and other power electronic devices, in order to handle higher currents. The control parameters require a number of extra menus to provide for intervention to the increasing hardware members. Especially because the adjustment of the torque according to the load within the car is very important, the controls require more sensitive load-measuring equipment at ultra-high speeds. When these elevators are used in towers in which complex traffic is present, they need to be smart and able to learn. Therefore, they generally need to operate with traffic redirection and monitoring devices, or possess equipment that provides remote intervention.

As the speed of the elevator increases, contemporary technology continues to allow for carrying out many operations, which were previously performed mechanically, with less material and more electronically. Systems such as PESSRAL and newly discovered materials will surely present new hardware in the future.