Question of Speed

A number of factors have a role in how fast elevators go — and how fast they need to.

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

Before we can answer that, we need to address the question, “What is the speed of a high-speed elevator?” Fundamentally, according to standards and regulations, there is no such concept as “high-speed elevator.” Having said that, in the article 5.5.6.1 of the TS EN 81-20 standard, the indication is 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 greater are considered high-speed, and they require the application of a different model.

There is no difference between 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. A compensation rope winds 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.

Minimizing Vibration

In order to minimize the vibration, several components and methods are employed. One of these is hanging weights on the bottom of the car, which will help it to remain at the center. The concrete weight of varying kilograms placed after the car’s installation is completed puts extra stress on the motor; however, the weights also reduce the sway of the car. In addition, car guide rails become more complicated components. The slide-type guide rails quickly become worn, due to the increasing friction as the speed rises and the differentiation of the friction surface area. This causes more vibrations, both in the vertical and horizontal axis.

Fundamentally, according to standards and regulations, there is no such concept as “high-speed elevator.”

Therefore, roller guide rails are preferred. This type of skate, which grasps the main rail with three or six wheels, depending on the design, is equipped with springs that have suitable rigidity to absorb the sway. As the speed increases — for example, as the speed goes up to 7 m/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 goes up to US$20,000 from US$9,000. With speeds over 10 m/s, which 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, to allow the car to slice through the air mass within the shaft. Increasing the amount and speed of air movement also increases the risk of failure due to 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.

Speed/Safety Connection

Increasing speeds cause the safety requirements to be increased and the connected safety components to be larger, both in terms of dimensions and features. Buffer strokes increasing considerably along with the speed create the need for deeper shaft bottoms. In this instance, elevator producers will use deceleration devices to decrease the impact speed of the elevators and thus prevent excessive stroke increase. These deceleration devices signal an electronic mechanism by detecting the position of the elevator while it is near the terminal floors by means of 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.

Other safety installations affected by speed are 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 using centrifugal force of a spring and thus tensing the mechanism. Motor brakes are larger in dimension and number.

In the same way, the number and quality of shaft information system components increase. Flag scanners having more scanning members and magnetic or barcode strips scanned by a speedometer across the shaft — plus improved encoder systems — are added to the hardware. The leveling differences caused by excessive stretching in the rope length, and 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 to prevent increasing the speed of the motor at ultra-high speeds. Several companies are experimenting with composite materials, which are lighter but have the same resistance as steel ropes.

Complicating Components

The control, software and the electric components 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 extra menus to provide for intervention to the increasing hardware members. Because the adjustment of 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 that were previously performed mechanically but are now enabled with less material and more electronic oversight. Systems such as PESSRAL and newly discovered materials will surely present new hardware in the future.