by Tadashi Munakata, Hideya Kohara, Kazuhiko Takai,
Youichi Sekimoto, Ryo Ootsubo and Shigeo Nakagaki
An elevator with the world's highest speed of 1,010mpm has been developed. As a result, various high-tech items have been newly created and applied to this elevator. The twin drive control technique for driving a powerful traction machine has been developed, and a safety device bearing with a temperature exceeding 1000°C under a high-speed run of 1,010mpm has been produced. An atmospheric pressure control system for riding comfort under a high-speed run has also been developed. Furthermore, we have analyzed mode shapes of rope by simulation and have designed the vibration-suppression system. These high-tech items have led to the successful construction of the elevator in the Taipei Financial Center, which is 508 meters high.
Introduction
The construction of the world's tallest building, the Taipei Financial Center, is fast underway (Figure 1). This building will have two elevators that can carry passengers from the ground floor to the highest floor in less than one minute at 1,010mpm, the fastest elevator in the world.
Table 1 shows the main specifications of these elevators. Toshiba Corp. has been pressing ahead with many research works and development projects to realize the world's fastest elevator with substantially surpassing speeds achievable now. The main development items are shown in Figure 2.
Currently, these developments are completed through evaluation using a prototype in our testing tower, and we are now waiting for an actual model reflecting all the acquired results.
Driving System
The driving system of the world's fastest elevator consists of a large two-winding permanent magnet synchronous motor (PMSM), a large-capacity converter/inverter system and a control system containing a vibration-suppressing controller.
Traction Machine
The traction machine is a newly developed two-winding PMSM as shown in Figure 3, a 650kW class maximum output, which can withstand up to 77 tons of sheave shaft load. The traction machine has a special frame structure to help avoid electromagnetic vibration. By optimizing the shape of the magnet, it avoids causing resonance during operation. These techniques greatly contribute to quiet operation at a rated speed of 1,010mpm, the accelerating and decelerating region.
In addition, to support the traction machine, Toshiba Corp. developed a dual, multi-stage vibration-isolating structure. As a result of simulation and experimentation, we found that it is almost twice the ratio of the vibration suppression of a conventional unit.
Control System
The control system consists of a twin drive system controlling two independent converters/inverters, which drive a large-capacity two-winding traction machine. The control circuit uses two high-performance MPU developed only for power electronics but succeeds in driving two independent converter/inverter driving systems, all under digital control. The converter/inverter contains six 1200V-600A class IGBT elements connected in parallel to drive the PMSM traction machine with maximum 650kW class output.
Vibration Suppressing Control
An elevator car travels a long hoistway at high speed. It is expected that a large elastic motion may occur on the ropes when the acceleration changes. Normally, the motor is driven with the PI feedback controller on the basis of
the error between the actual rotational speed of the main sheave and the speed reference. Since the main sheave rotation goes behind control reference, the motor torque that the controller calculates is generally compensated with a feed-forward controller. However, in the elevator system with a long hoistway, the influence of the rope elasticity should also be compensated. A two-degrees-of-freedom servo system was introduced to compensate the delay of sheave rotation and the rope elasticity. The more comfortable ride can be realized by the motor control techniques.
A newly developed ripple canceller is also equipped in this system. The angular velocity signal from a rotation detector contains harmonic waves. The ripple canceller cancels these harmonic waves by generating counter sine waves, which frequency varies with angular velocity automatically. Every ripple components of the motor torque, which is caused by the harmonic waves of a rotation detector, can be reduced, regardless of the main sheave rotation speed. Figure 4 shows the operation waveform of the driving system. This technique significantly enhances the riding comfort of elevators at high speed.
Car System
Atmospheric Pressure Control
In the Taipei Financial Center, the elevator has a hoistway of 388 meters high. So, it goes up at a maximum speed of 1,010mpm taking about 38 seconds. It goes down at a maximum speed of 600mpm taking about 48 seconds. The difference in atmospheric pressure between the starting floor, and the destination floor is about 48 hPa and a sudden change in pressure in the elevator may cause discomfort. Therefore, a pressure control system was introduced for the first time in the world to an elevator system for improving riding comfort.
To develop a pressure control system, it is necessary to get the pressure change pattern to enhance riding comfort for passengers. For this reason, a decompression test facility was introduced that can reproduce the pressure change in the elevator, and a monitor evaluated the riding comfort. Normally, a pressure change begins slowly at first, speeds up and slows again. To enhance riding comfort without changing the hoistway length and traveling time, it is necessary to control the pressure change from the start of the journey until it ends and generates the most comfortable pressure change pattern in the elevator car. The most favorable pattern of pressure change was the one that changes at a fixed rate from start to stop as the result of testing in Figure 5(a). This means that the maximum rate of change of pressure has to be reduced as the elevator goes up and down the hoistway. In the Taipei Financial Center, the maximum rate of change of pressure can be reduced from 2.0 hPa/s to 1.26 hPa/s and this is 37% down against a system without pressure control.
Using these results, Toshiba Corp. developed a pressure control system to control the pressure in the elevator car. As a mechanism to generate sufficient pressure difference, a high-pressure blower was adopted to make this system failsafe even if a control error occurs. The panels, constituting a car enclosure, are dual panel structured to increase air-tightness and to reduce deformation due to applied pressure load. In addition, the pressure control adopts a method of controlling the pressure difference between the inside and outside of the car enclosure. Figure 5(b) shows the pressure difference between the inside and the outside of the car enclosure when a pressure control is applied. The control was programmed to follow the control command to make the rate of change of pressure constant. The results were excellent.
Aerodynamic Capsule
The wind noise varies from the sixth to eighth the power of the traveling speed. Therefore, the wind noise which generates in conventional elevators, cannot be ignored when the elevator travels at 1,010mpm. As shown in Figure 6, this elevator has an aerodynamic capsule attached to the car with the airflow streamline to reduce noise. We analyzed airflow in the hoistway and the surface pressure of the aerodynamic capsule. Through such analysis, we optimized the shape of the aerodynamic capsule to reduce the wind noise and applied a damping material in noise-prone areas.
The walls of the car are dual-structured except for the car entrance section and have sufficient sound insulation. Moreover, the entrance section has relatively less sealing due to the opening and closing motion of the door panel and with noise from outside likely to enter the car. For this reason, we modified the wedge-shaped spoilers mounted at the top and bottom ends of the capsules so that most of the airflow generated flows toward the sides and back of the car when the car travels. In addition, we modified the spoiler mounted beneath the door for the airflow coming through the entrance section along the streamline and also widened the gap between the doorsill and the hoistway wall to reduce the wind noise. Analyzing these effects using the prototype unit, we predicted that the air resistance generated around the car when traveling at 1,010mpm might be reduced to the same level of conventional elevators traveling at 600mpm.
New Type Roller Guide
Shaking forces have influence on an elevator during high speed, running along the distorted or undulated guide rails, other than air resistance. We designed a new type roller guide with proper allocation of forcing spring and having the optimum balance weight. This roller guide isolates shaking force and leads to a comfortable ride. The advantages of the new type roller guide are:
(1) Force from rail is fully received by soft spring; and
(2) Impulsive force is absorbed by balance weight. The reduction ratio of the car-shaking force against the shaking frequency, in comparison with a conventional unit, is 25% at 10Hz and 65% at 30Hz.
Safety System
Governor
We changed the type of governor from a conventional gear type to a new type in which lightweight flyballs are mounted directly on the inside of the sheave so that the flyballs and the sheave rotate together to detect centrifugal force. Thus, we made an operating mechanism whose structure is simplified and the centrifugal force that varies as the speed increases is lowered, and thus can accurately transmit the speed change. Rope-gripping performance deteriorates due to reduced friction coefficient at high speed, so we lowered the contact angle used when the rope-gripping sequence starts. The longer the car runs, the more bearer the friction material is. So, we made 170% length of the friction material than ever. With this, the rope-gripping performance at high speed has the same stable performance as that of conventional models.
Safety Device
We developed a safety device with an operation speed of 1,275mpm and a maximum applicable mass of 22.7 tons. The maximum braking energy is 13.7 MJ, and this is about 3.1 times that of a conventional safety device. The braking distance from the safety device being applied to the car finally stopping, is approximately 40 meters. The surface temperature of the safety shoe exceeds 1,000°C. Therefore, we developed a special type of silicon nitride ceramic, which has excellent heat resistant and wear-resistant characteristics. We also applied grooves to the surface to obtain a high-friction coefficient. In addition, as the operation speed becomes high, the mechanical shock grows large, we adopted the highest strength material for the device's main body and analyzed by FEM that we obtained to ensure sufficient strength. Finally, at our testing tower, we performed a drop test as many as 60 times to optimize the alignment shape of the safety shoe and spring force to check sufficient braking characteristics and durability. The result of the drop test performed at our testing tower is shown in Figure 7.
Oil Buffer
If a conventional single-stage plunger structure is used, it reaches 17 meters, and a deep pit is needed. Therefore, we developed a telescopic type oil buffer, which extends in multiple stages and reduces the total length by 40%. This device is designed applying a terminal-speed limiting device. We developed this device with a maximum crash speed of 679mpm and a maximum applicable mass of 11.4 tons. A three-stage telescopic type plunger extends with each stage, interlocking at a stroke ratio of 2:2:1 by means of an internal hydraulic circuit. A total length of 10 meters, and a stroke of 6 meters were realized. We adopted a multi-pore type orifice and obtained optimal damping for use at high speed with large masses by evaluating damping through the analysis. In addition, we decided to use a gas spring as a re-extension mechanism for the plunger to make it small.
Vibration Suppression of Ropes
High-rise buildings have lower natural frequencies than conventional buildings. The natural frequency of the ropes varies with time due to the up or down travels of the car. Consequently, in high-rise buildings, the elevator rope may resonate with the building and may hit some hoistway equipment. Therefore, we analyzed lateral vibration of the elevator ropes for high-rise building induced by wind forces numerically. From these results, we have taken safety measures such as a vibration suppressor (installation of a suppressor against the rope deflection) and high-wind emergency operation (a reduced speed operation or a stop operation according to the building sway).
The calculated results of mode shapes when the elevator is ascending is shown in Figure 8, considering the time-varying length. The relation between the building sway and the rope deflection was obtained through numerical calculation. In addition, the mode shapes when the rope collides with vibration suppressor is shown in Figure 9. The vibration suppressor was designed by using the calculated results such as the load applies to the suppressor and the effective number of suppressor against the rope deflection.
Conclusion
We have developed various high-tech products by simulation or experiment. These techniques have applied to an elevator with the world's fastest speed of 1,010mpm. High-rise buildings are becoming increasingly common even in Asian countries to cope with dense concentrations of population and industry. It is expected that high-speed and high-rise elevators will be increasingly needed, the elevator being the only vertical transportation system in metropolitan space. Our new technique may be expected to contribute to these elevators for high-rise buildings. Toshiba Corp. is ready to provide elevators complete with safety, comfort and features of convenience using technology acquired from developing the world's fastest elevators for the Taipei Financial Center.
Reprinted from the International Association of Elevator Engineers (IAEE) in Elevator Technology 12, Proceedings of Elevcon 2002, the 12th International Congress on Vertical Transportation Technologies, held June 25-27, 2002 in Milan, Italy.
Tadashi Munakata joined Toshiba Corp. in 1975 and is presently a senior manager in the Engineering Division R&D Center, Toshiba Elevator and Building Systems Corp.
Hideya Kohara joined Toshiba Corp. in 1990 and is presently a deputy manager in the Mechanical Development Group, Engineering Division R&D Center, Toshiba Elevator and Building Systems Corp.
Kazuhiko Takai joined Toshiba Corp. in 1998 and is presently a mechanical engineer in the Mechanical Development Group, Engineering Division R&D Center, Toshiba Elevator and Building Systems Corp.
Youichi Sekimoto joined Toshiba Corp. in 1991 and is presently a deputy manager in the Electrical Development Group, Engineering Division R&D Center, Toshiba Elevator and Building Systems Corp.
Ryo Ootsubo joined Toshiba Corp. in 1995 and is presently an electrical engineer in the Electrical Development Group, Engineering Division R&D Center, Toshiba Elevator and Building Systems Corp.
Shigeo Nakagaki joined Toshiba Corp. in 1979 and is presently a manager in the Elevator Systems R&D Center, Electrical and Mechanical Systems R&D Department, Power and Industrial Systems R&D Center, Toshiba Corp.