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several technical problems to be paid attention to in elevator selection
Sep 26, 2018

With more and more buildings equipped with elevators, more and more investors and design units will encounter such problems - how to choose elevators for their projects? This article combines some technical problems of the elevator to talk about some points that should be paid attention to when selecting the configuration.

1. The main parameters determining the conveying capacity - the number of elevators, the carrying capacity and the rated speed

The elevator should have appropriate transport capacity. The conveying capacity can meet the laddering requirement of the peak period of 5 minutes, and the selection of the elevator can be considered reasonable. The time interval between the elevators reaching the foyer should not be too long. General requirements should not exceed 2-3 minutes. Simple estimation method: the elevator should not reach 45~60s from the bottom to the top. Waiting time and boarding time should be as short as possible. This is to meet the psychological requirements of passengers. The more acceptable limits are: the waiting time is no more than 30s, and the boarding time is no more than 90s. What is worth noting at the moment is the tendency to blindly pursue the speed of the elevator. High-speed elevators do not necessarily shorten the boarding time and improve the transportation efficiency. In fact, we must also consider the height of the building, the number of stops and the scheduling technology. For buildings that are not too high and have a large number of stops, high-speed elevators can only operate at medium and low speeds, while high-speed elevators and medium-speed ladders stop. There is no difference between the opening and closing time of the door and the passenger's access time. In order to improve the efficiency of elevator operation and reduce passengers' boarding time, new technologies such as direct stop, early door opening and quick closing are emerged in recent years. The direct stop is to cancel the low-speed leveling section in the running curve, and the elevator is reduced from the rated speed to a zero speed at a certain deceleration, which is exactly the leveling position. If there is a slight deviation, it can be adjusted by the technique of “re-leveling”; opening the door in advance means that the car has not reached the zero speed, that is, the door opening machine starts to operate within a small safety distance that is not completely leveled, and the car is completely accurate. The door is basically opened; the quick closing means that the average closing speed is increased under the premise of satisfying the maximum blocking closing force and the maximum kinetic energy limit of the door, thereby shortening the closing time. These measures seem to save a lot of time in the leveling and opening and closing process of each stop, but the cumulative effect of many landings is much better than simply increasing the speed of the elevator.

2. Technical performance that needs to be considered - reliability, advancement and comfort

The so-called reliability refers to the ability of the elevator system to maintain a prescribed function within a prescribed time, and is a probability concept based on a large amount of statistical data. Our reliability requirements for elevators mean that there are as few faults as possible during the run time and can be easily eliminated in the event of a fault. The links that affect personal safety, such as speed limiters, safety touch panels, and grating door zone protection systems, must not fail. The advanced nature of elevators is mainly reflected in the technology of drag and control. With the development of power electronics technology and computer technology, fundamental progress has been made. The vector-controlled frequency modulation and voltage regulation technology (VVVF) makes the adjustment of AC asynchronous motor. The speed performance reaches the level of the DC motor. The logic control system using the computer is replacing the relay and the control function of the elevator is continuously increased. The application of the network control and fuzzy control theory makes the elevator dispatch control develop toward the intelligent direction.

Comfort mainly refers to the acceleration, vibration, noise, decoration, lighting and other indicators of the elevator. Its purpose is to provide passengers with a comfortable environment for riding. The early comfort requirements are mainly to control the overweight and weightlessness, the noise and anxiety, and the range that passengers can tolerate; the modern comfort is to make the passengers not only physically and psychologically take the elevator as " Enjoy up and down." Obvious reliability is the most important indicator when selecting an elevator. The national standard GB10058 stipulates that: the elevator operates 60,000 times and the failure is less than 5 times is a qualified product, less than 2 times is a first-class product, less than 1 time is a superior product, and the fault is defined in Appendix B. In addition to the tendency to ignore reliability, there is a tendency to pay attention to the current pursuit of comfort. Some projects in the elevator selection time to observe the slight vibration, noise and the "beauty effect" of the installation, which is not very good for other technical problems, and ultimately caused the selection mistakes. This kind of case can be said to be common.

3. Drag control mode - AC two-speed, voltage regulation and frequency modulation

The elevator speed is zero when the elevator stops. In normal operation, the linear motion is performed at a constant speed at a rated speed. The acceleration or deceleration transition is made between zero speed and rated speed. The control of the motor speed during this period is called speed regulation. When the car accelerates or decelerates, the passengers will be overweight and lose weight. Ordinary people's ability to withstand overweight and weightlessness is very limited. China's national standard GB10058 stipulates that the value of a should not exceed 1.5m/s2. In addition, if the acceleration is always tired, the passengers will have a bumpy feeling and even dizziness. This requires that the rate of change of acceleration be as small as possible. The DC motor has good speed regulation performance, but the DC motor is powered by the collector ring, and the maintenance workload is large. AC asynchronous motor has simple structure and reliable operation. With the development of computer and power electronics technology, different speed control methods are used to meet the needs of different elevators. Low-speed elevators often use the AC two-speed (AC-2) scheme, with fewer control links and lower failure probability. The main disadvantage is that leveling accuracy and ride comfort are difficult to achieve. Medium-speed elevators use voltage regulation (ACVV) technology. This speed regulation method changes the torque of the motor by changing the voltage. By adjusting the difference between the motor torque and the load torque, the positive and negative angular accelerations of the motor are controlled, and the elevator is controlled by the full closed loop control mode. It runs at speed and acceleration and has become the leading product of domestic elevators.

In the past decade, a new technology for frequency modulation and voltage regulation (VVVF) has emerged. This kind of speed regulation technology has developed rapidly, and its speed regulation performance is completely comparable with that of DC motors. In addition to good comfort, the leveling accuracy is greatly improved, and it has obvious energy saving effect.

4. Signal control methods - relays, PCs and microcomputers

When passengers take the elevator, they must first give the elevator a call signal on the floor where they are located. After entering the elevator car, they must register the floor signal they want to go. These numbers will appear randomly at random, and the elevator's signal controller will continuously record and arrange the execution order, which is the signal control or logic control technology of the elevator. In the early elevators, the driver usually processed the signals and issued commands. This control is called signal control. Later, the logic line is used to respond and execute according to the prescribed procedure. The elevator can be operated by the driver or without the driver. This control is called the collection control. When the elevator hall is equipped with 2-3 elevators, these elevators can be automatically scheduled in a prescribed order by a common call button. This control is called parallel control. When there are multiple elevators installed side by side, the number of signals is greatly increased. The controller shall automatically dispatch the elevators according to the scheduled dispatching technology to respond to the call requirements of each landing station according to the scheduled dispatching technology. This control is called Group control.

Signal control and simpler set control are implemented by relays for a longer period of time. Later, with the development of computer technology, the industrial general-purpose programmable controller - PC. In the case of a large number of landings and functional requirements, many elevator companies have developed dedicated microcomputer control systems using 8-bit, 16-bit or even 32-bit microcontrollers, as well as new technologies such as serial communication and microcomputer network control. The fuzzy control theory was introduced in the design, which made the elevator significantly improve the reliability and scheduling efficiency of many new functions.

5. A type of machine that should be paid attention to - hydraulic elevator

The uniform linear motion when the hydraulic elevator car rises is realized by injecting oil into the cylinder at a certain flow rate to increase the plunger at a constant speed. The uniform linear motion during the lowering is discharged by the oil in the cylinder at a certain flow rate. Into the fuel tank, the car's own weight makes the plunger drop at a constant speed, there is also a speed regulation problem. There are generally two ways when the car rises. One is volumetric speed regulation, or it is called pump-controlled cylinder speed regulation, and the other is throttling speed regulation, or valve-controlled speed regulation. Throttling speed regulation is generally used when the car is lowered. The advantages of the hydraulic elevator are that it has low requirements on the machine room, has a large carrying capacity, and has fewer safety problems. The disadvantage is that the lifting height is limited, generally no more than 6 floors; the speed of the elevator can not be very fast, generally should not exceed 1m / s. Freight elevators, especially those with large tonnage (above 2t), should be preferred for hydraulic elevators. When an elevator is added to an old building, it is difficult to find a suitable machine room and a hoistway. At this time, the hydraulic elevator shows obvious advantages. In addition, if the villa-style 2-3 storey house needs to be equipped with an elevator, the hydraulic elevator is undoubtedly the most ideal model.

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