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Several technical issues that must be paid attention to when selecting elevators

Update:2020-12-02
Abstract:

As more and more buildings are equipped with elevators, […]

As more and more buildings are equipped with elevators, more and more investors and design units will encounter such a problem-how to choose elevators for their projects? This article discusses some key points that should be paid attention to when selecting and configuring elevators in combination with some technical issues.

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

The elevator should have an appropriate conveying capacity. If the conveying capacity can meet the elevator requirements during the 5-minute peak period, it can be considered that the elevator selection is reasonable.
The time interval for the elevator to reach the lobby should not be too long. Generally, it should not exceed 2-3 minutes. Simple estimation method: it should not exceed 45~60s from the bottom to the top of the elevator.
The waiting time and boarding time should be shortened as much as possible. This is to meet the psychological requirements of passengers. The more acceptable limits are: the waiting time does not exceed 30s, and the riding time does not exceed 90s.
At present, it is worth noting the tendency to blindly pursue elevator speed. High-speed elevators will not necessarily shorten the time of taking the elevator and improve the efficiency of transportation. In fact, the height of the building, the number of stops and the dispatching technology must be considered. For buildings that are not too high and have a large number of stops, high-speed elevators generally can only run at medium and low speeds, while high-speed and medium-speed elevators stop at floors. There is no significant difference between the opening and closing time and the time of passengers entering and leaving. In order to improve the efficiency of elevator operation and reduce the time for passengers to take the elevator, in recent years, new technologies such as direct parking, early door opening, and fast door closing have emerged. Direct parking means that the low-speed leveling section is cancelled in the running curve, and the elevator decelerates from the rated speed to zero speed, which is exactly the leveling position. If there is a slight deviation, it can be adjusted by "re-leveling" technology; opening the door in advance means that the door opener starts to move within a small safe distance before the car has reached zero speed, that is, the car is not completely leveled. The door has been basically opened at the time of the first floor; fast closing means that the average door closing speed is increased under the premise of meeting the maximum blocking force and the maximum kinetic energy of the door, thereby shortening the closing time. These measures do not seem to save much time during the leveling of each stop and the door opening and closing process, but the cumulative effect of many floors is much better than simply increasing the elevator speed.

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 the specified functions within a specified period of time. It is a probability concept based on a large amount of statistical data. Our reliability requirements for elevators mean that there should be as few failures as possible during the running time, and that failures can be easily eliminated once they occur. The links that affect personal safety, such as safety gear, speed limiter, safety touch panel, and grating door zone protection system, must never fail. To
The advancement of elevators is currently mainly reflected in the driving and control technology. With the development of power electronics and computer technology, fundamental progress has been made. The vector control frequency and voltage regulation technology (VVVF) makes the AC asynchronous motor adjustable The speed performance has reached the level of DC motors. Computer-based logic control systems are replacing relays and increasing the control functions of elevators. The application of network control and fuzzy control theory has made elevator dispatching control intelligent.
Sense of comfort mainly refers to the elevator's acceleration, vibration, noise, decoration, lighting and other indicators. Its purpose is to provide passengers with a comfortable riding environment as much as possible. Early comfort requirements were mainly to control overweight and weightlessness, annoyance and anxiety, etc. within the range that passengers can tolerate; modern comfort seeks to make passengers treat elevators not only physically but also psychologically. Enjoy up and down".
Obviously reliability is the most important indicator when selecting elevators. The national standard GB10058 stipulates that: the elevator runs 60,000 times with less than 5 failures as qualified products, less than 2 times as first-class products, and less than 1 time as excellent products, and the failure is defined in Appendix B. At present, in addition to the tendency to ignore reliability, there is also a tendency to pay attention to excessive pursuit of comfort. In some projects, the elevator's slight vibration, noise, and the "aesthetic effect" of the decoration were noticed at the time of elevator model selection, but they were not so much about other technical problems, and eventually caused model selection errors. Such cases can be said to be common.

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

The elevator speed is zero when the elevator stops. In normal operation, it makes a uniform linear motion at the rated speed. The acceleration or deceleration transition is made between zero speed and rated speed, and the control of the motor speed during this period of time is called speed regulation.
When the car is accelerating or decelerating, passengers will experience overweight and weightlessness. Ordinary people's ability to withstand overweight and weightlessness is very limited. my country's national standard GB10058 stipulates that a value should not be greater than 1.5m/s2. In addition, if the acceleration is always fatigued, the passengers will feel bumpy and even dizzy. This requires the acceleration rate of change to be as small as possible. The DC motor has good speed regulation performance, but the DC motor uses a slip ring to supply power, and the maintenance workload is relatively large. AC asynchronous motors are simple in structure and reliable in operation. With the development of computer and power electronic technology, different speed regulation methods are used to meet the needs of different elevators. Low-speed elevators often adopt AC two-speed (AC-2) scheme, with few control links and low failure probability. The main disadvantage is that it is difficult to balance the leveling accuracy and ride comfort. Medium-speed elevators mostly use 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 acceleration of the motor are controlled, and the elevator is controlled by a fully closed loop control method. It runs at high speed and acceleration and has now become the leading product of domestic elevators.
In the past decade, a new technology of frequency and voltage regulation (VVVF) has emerged. This kind of speed regulation technology has developed rapidly, and its speed regulation performance is completely comparable to that of DC motors. In addition to having a good sense of comfort, the leveling accuracy is also greatly improved, and it has obvious energy-saving effects.

4. Signal control method-relay, PC and microcomputer

When a passenger takes an elevator, he must first give the elevator a call signal on the floor where he is located, and register the floor signal he wants to go to after entering the elevator car. These numbers will appear randomly, and the signal controller of the elevator must continuously record and arrange the execution sequence. This is the signal control or logic control technology of the elevator. In the early elevators, the driver generally processed signals and issued instructions. This kind of control is called signal control. Later, logic lines are used to respond and execute according to the prescribed procedures. The elevator can be operated by a driver or without a driver. This kind of control is called collective control. When the elevator hall is equipped with 2-3 elevators, the common call button can make these elevators automatically dispatch in a prescribed order. This kind of control is called parallel control. When multiple elevators are installed in parallel, the number of signals increases greatly. The controller should quickly and quickly dispatch the elevators according to the established dispatching technology according to the operation of all elevators to answer the call requirements of each floor. This kind of control is called For group control.
Signal control and relatively simple collective control are implemented by relays for a long period of time. Later, with the development of computer technology, a general-purpose industrial programmable controller-PC appeared. In the case of high number of floors and functional requirements, many elevator companies have used 8-bit, 16-bit or even 32-bit single-chip microcomputers to develop special microcomputer control systems, and also adopt new technologies such as serial communication and microcomputer network control. Fuzzy control theory is introduced in the design, which increases the reliability of the elevator and significantly improves the dispatching efficiency.

5. A model that should be paid attention to-hydraulic elevator

The uniform linear motion of the hydraulic elevator car is realized by injecting oil into the cylinder at a certain flow rate by the oil pump to make the plunger rise at a constant speed. Into the fuel tank, the weight of the car makes the plunger drop at a constant speed. There is also a speed regulation problem. There are generally two ways when the car is ascending, one is volumetric speed regulation, or pump-controlled cylinder speed regulation, and the other is throttle speed regulation, or valve-cylinder speed regulation. Throttle speed regulation is generally adopted when the car is descending.
The advantages of hydraulic elevators are low requirements for the machine room, greater carrying capacity, and fewer safety issues. The disadvantage is that the lifting height is limited, generally no more than 6 floors of buildings; the speed of the elevator can not be very fast, generally should not exceed 1m/s. To
Freight elevators, especially those with large tonnage (above 2t), should be given priority to hydraulic elevators. When adding elevators to old buildings, it is difficult to find a suitable machine room and hoistway. At this time, hydraulic elevators show obvious advantages. In addition, hydraulic elevators are undoubtedly the most ideal model for villa-style 2-3 storey residential buildings.

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