With the rapid development of my country’s economy, the elevator market is extremely prosperous, with an annual demand of more than 40,000 units, making it the most active market in the world. Because the elevators in our country are greatly influenced by Japanese products, people have higher and higher requirements for the comfort of elevators. How to improve the comfort of elevator operation has become an important issue that various elevator manufacturers pay attention to.
Second, choose a high-quality and stable traction machine
The elevator control system should first be said to be a mechanical system. The operation of the elevator is the reciprocating mechanical movement of the car on the guide rail. Due to its function of carrying people, strict requirements are put forward for its reliability, vibration, noise and comfort. The reliability of elevator machinery can be fully guaranteed by mechanical design and material selection. The mechanical vibration of the car in the X and Y directions is completely guaranteed by the installation of the guide rail and the machining accuracy and quality of the guide shoes, while the mechanical vibration in the Z direction is closely related to the traction machine, its driving motor, and the frequency converter.
The traction machine is the driving device for elevator operation, and its performance is directly related to the comfort of elevator operation. The impact of the mechanical clearance of the traction machine on the elevator is mainly reflected in the acceleration and deceleration process of the elevator. When the motor speed changes, the electric operation and power generation operation state will switch, causing the vibration of the elevator, which greatly affects the comfort of the elevator. . During the S-curve acceleration and deceleration process of the elevator, there are usually one or two obvious weightlessness or overweight sensations, accompanied by abnormal noises from the traction machine. In addition, for some modified two-speed old elevator traction machines, due to the huge impact of multiple high and low speed switching, the rubber gasket in the connecting sleeve shaft is severely worn, which will also cause the above phenomenon. Therefore, elevator manufacturers must set clear requirements for the clearance of the newly selected traction machine, and regularly check the wear of the connecting shaft during maintenance.
In addition, poor processing and installation accuracy of the internal gear or worm gear of the traction machine, poor dynamic balance adjustment will also cause vibration and noise when the elevator is running at high speed. The author once worked in a certain manufacturer and found that the vertical vibration of the elevator was particularly large. When all methods were ineffective, it was suspected to be a problem with the traction machine. traction machine, the problem is solved. As a result, the problem is that the traction machine manufacturer is small in scale, and its testing methods are outdated. It is difficult to guarantee the consistency of the traction machines produced, which has caused significant direct and indirect losses to the elevator factory. Therefore, the choice of traction machine should not be greedy for cheap, but must choose a manufacturer with strong technical strength, complete testing methods, and a sound quality assurance system. Another point to be emphasized is that in the case of the same elevator speed, it is better to choose a traction machine with a large reduction ratio of the traction machine. Because the deceleration ratio is large, the backsliding phenomenon caused is small, and the starting comfort is easy to adjust. Practice has proved that at the same elevator speed, the starting comfort of the traction machine with 6-pole motor is worse than that with 4-pole motor. The essential reason is that the starting torque of a 6-pole motor is not greater than that of a 4-pole motor by 1.More than 5 times.
Third, select high-quality driving motor
Under the premise of ensuring the quality of the traction machine, the performance of the motor matching the traction machine is also directly related to the starting and braking process of the elevator The performance of the car, the problem is mainly manifested in the quality of the starting comfort. If the starting torque of the motor is large, the reverse slip will be very small when the elevator releases the brake. At present, in many frequency converter manuals, there are statements that seriously mislead users. The frequency converter can achieve a starting torque of 200% or even 300%, which is actually meaningless. If the designed starting torque and maximum torque of a motor are small, no matter how good the frequency converter is, it will not produce large output torque, and it is also prone to speed fluctuations, resulting in oscillation.
According to the basic knowledge of asynchronous motors, the M-N curve of the motor is shown in Figure 1(a). Point A in the figure is the initial starting torque point, point B is the maximum torque point, and point C is the rated operating point. The starting torque of the motor is related to the slip rate s of the motor. If the slip is large, the initial starting torque is large. To increase the slip, the rotor resistance is required to be large and the rotor inductance is small. Figure 1(b) shows that the rotor resistance is different The mechanical characteristic curve of the case. It can also be seen from the figure that as the rotor resistance increases, the maximum torque does not change, but the corresponding maximum slip increases, and the slip also increases under the same load. This is why imported brand elevators use high-slip motors. However, in order to reduce costs, many imported brand traction machines are equipped with domestic low-slip motors. The slip frequency is generally less than 2.5Hz, and their starting performance is greatly reduced. Therefore, when choosing a traction machine brand, the choice of the brand and performance of its matching motor is equally important.
Fourth, choose a frequency converter with excellent performance
The vector control of asynchronous motor is based on the vector control of the motor parameters, so the motor parameters must be able to learn automatically. Otherwise, superior performance cannot be obtained. Therefore, first of all, a frequency converter that can perform self-learning of motor parameters must be selected. Secondly, the frequency converter must have a torque output of more than 150% of zero speed, which can ensure good starting and parking comfort. In addition, it needs a very good overload capacity, 110% of the rated load, and must run continuously, especially for high-rise elevators, which need to run at full load for more than 30S, and this must be considered. Some inverters from foreign manufacturers, 100% rated load, can not run continuously for 60S, therefore, when it is used for high-rise elevator control, it is recommended to enlarge the first gear to use, causing unnecessary economic losses to users.
After selecting the inverter, to achieve a better sense of comfort, the key is to adjust the performance and operating curve of the inverter. When the elevator starts, due to the relatively large static friction of the mechanical guide shoe, it can be eliminated by adjusting the starting speed and the time to maintain the starting speed. In addition, general frequency converters have the function of speed loop PI parameter adjustment. By adjusting the speed loop PI parameters, the dynamic response speed and steady speed accuracy of the frequency converter can be effectively adjusted, which can improve the comfort of elevator start-up and steady-state operation. The starting performance is related to the low-frequency PI parameter. You can first set the low-frequency I to zero or a relatively large value, and adjust KP without considering the leveling accuracy. Increasing KP will speed up the low-frequency dynamic response and increase the starting torque, but KP is too high. Large, it is easy to cause oscillations, and the comfort of starting and parking crawls will be poor. Therefore, it is necessary to increase KP until the elevator does not oscillate under full-load and no-load conditions, and then gradually reduce the I parameter to achieve the satisfactory effect of starting and crawling. The principle of high-frequency PI parameter adjustment is to ensure the minimum overshoot in the process of starting acceleration and stopping deceleration, generally less than 2% of the rated speed, and to ensure the speed accuracy under the condition of steady speed, generally not exceeding 0.001m/s. First set the high-frequency I to zero or a relatively large value, adjust K so that the parameter is less than the critical parameter for the elevator to oscillate in the high-frequency steady state, and then gradually reduce I to make the overshoot reach the required index. For the occasions where the same traction machine and machinery are used, the copy can be realized by copying the keyboard parameters when one elevator is adjusted. In the above, the unit of the integral time constant I is the time unit S. It is especially reminded that the PI parameters of most inverters currently on the market are adjusted by two independent numbers, without the concept of actual physical quantities. The larger I is at this time, the smaller the time constant is.
For the comfort during acceleration and deceleration, it should be solved by S-curve adjustment. Generally, the acceleration and deceleration are between 0.5 and 1, the rapid acceleration at the beginning and the rapid deceleration at the end can be adjusted to 0.25~0.5, the rapid acceleration at the end and the rapid deceleration at the beginning can be between 0.5 and 0.9. The adjustment of the S-curve is also related to the location of the elevator. For hospitals, nursing homes and other occasions that require high comfort, the corresponding parameters need to be reduced. For office and office writing and other occasions that require high efficiency, the corresponding parameters can be appropriately increased. The increase of rapid acceleration at the end and rapid deceleration at the beginning is beneficial to overcome the jitter in the acceleration and deceleration process caused by the gap.
Fifth, adopt the optimal control sequence
The optimal control sequence is shown in Figure 2. After the inverter receives the operation command, it first enters the zero-speed operation process and delays T1. Ensure that the motor excitation reaches a steady state and then open the brake, and at the same time the inverter starts to run at the startup speed. After T2, it is high speed, low speed to zero speed.When the inertia effect is guaranteed to be zero, close the brake. Since it takes a certain time for the brake to hold tightly, it is necessary to cancel the operation command after a delay of T4. Following this sequence, ideal comfort is guaranteed both when starting and stopping. In the Emerson TD3100 inverter, T1 is set by F7.00, T2 is set by F3.01, T3 is set by F7.01, and T4 is determined by the control. If the delay time of the controller is not enough, the TD3100 inverter will automatically extend the command keep time.
1. Start-up compensation
For medium and low-speed elevators below 1.75m/s, due to the low running speed, there is basically no need for start-up compensation to achieve satisfactory results. Degree. For medium and high-speed elevators above 1.75m/s, if the requirements for starting comfort are relatively high, a weighing device must be added to compensate the starting torque. Generally, there are two kinds of weighing devices, switch quantity detection and analog quantity detection. The switching value detection has low cost, but it can only be graded. Generally, 4 switches are installed, and any 4-point accurate compensation can be realized between no-load and full-load. However, due to the graded compensation, it cannot be achieved. Ideally. The analog sensor can achieve stepless compensation, but the problem is that the output of the analog sensor often shifts with the use of the elevator, resulting in compensation errors, and the effect is sometimes worse than no compensation, so it is necessary to regularly adjust the compensation gain Make adjustments. The starting torque compensation principle of Emerson TD3100 elevator special inverter is shown in the figure
2. Reasonable selection of shock absorbers and wire ropes
Many elevator manufacturers are very random in the selection of shock absorbers. In fact, the shock absorber plays a very important role in improving the comfort of the elevator. The shock absorber generally has a rubber shock absorber at the base of the traction machine, a shock absorber spring or rubber shock absorber at the bottom of the car, and a rubber shock absorber at the top of the car.There are three types of wire rope shock absorbers. The quality and damping effect of the vibration damping pads on the base of the traction machine vary widely, which directly affects the comfort of the elevator, especially when the elevator goes up to the top 2 to 4 floors to start and stop, the problem will be extremely prominent. The quality of the shock absorber at the bottom of the car will directly affect the stability of the elevator’s steady-state operation. If the elastic coefficient is large and the characteristics are too hard, it will not be able to reduce the vibration, and high-frequency vibration will occur, and the human body will feel numb. When it is serious, it will cause high-frequency vibration of the car and generate relatively loud noise. On the contrary, low-frequency oscillation will be generated, causing the human body to sink. Therefore, it must be chosen reasonably. The vibration damping effect of the steel wire rope is the same as that of the shock absorber at the bottom of the car. A steel wire rope with a reasonable elastic coefficient must be selected according to the height of the floor to achieve a good vibration damping effect when the amount of expansion and contraction meets the requirements under full load. In addition, on high-rise elevators, due to the long wire ropes, when the consistency of tightness is poor, it is easy to cause the swing of the wire ropes during high-speed operation, and the collision with each other causes the vibration of the car. An effective method is to add a wire rope shock absorber at the end of the wire rope, which can effectively absorb the vibration wave of the wire rope and prevent the reflection from forming a beat phenomenon.
3. Reasonable selection of encoder
Encoder is a necessary device for the closed-loop of the elevator frequency converter, and its reasonable selection has a great impact on the safe and reliable operation of the elevator. From the installation method, the sleeve type is more reliable, but the price is slightly more expensive than the coupling type. At present, many manufacturers who use coupling encoders, because the standard couplings are easy to break when the coaxiality is not good, and the reliability is very poor, they use a very simple connection method to bring safety to the operation of the elevator. Hidden danger. In terms of wiring mode, there are push-pull output and open-collector output. It is recommended to use an open-collector encoder when the encoder connection exceeds 5m to improve the anti-interference ability.
The pulses per revolution of the encoder is generally above 300 to ensure the normal operation of the inverter. It is recommended that if the cost permits, it is best to increase the pulses per revolution of the encoder to 1000 to 2000, which can greatly improve the elevator performance. start-up comfort. The reason is that the larger the number of pulses per revolution, the easier it is to quickly detect the start of the car, so as to achieve the rapid adjustment of the torque and reduce the car slip.
4. Reasonable grounding of the control system
In the elevator control system, grounding is a key issue affecting reliability. Due to the non-standard power supply in our country, most of the occasions are three-phase four-wire system instead of three-phase five-wire system, and the grounding problem becomes more prominent. During installation and commissioning, it is first necessary to ensure that the control cabinet, traction machine and car are reliably grounded or grounded, and then the encoder is grounded. However, it should be emphasized that the standardization of encoders on the market is poor, and some encoders have poor anti-interference ability. It is a very serious mistake for the designer to connect the shielding layer of the encoder lead wire to the encoder shell. If the user connects the shielding layer of the encoder to the ground of the frequency converter, since the two ends are grounded, there will be a potential difference between the frequency converter and the motor, which will easily cause interference.The low-frequency jitter and random over-current protection of the elevator. In severe cases, when the traction machine is not grounded or the grounding is poor at the commissioning site, the electric leakage of the motor will cause serious damage to the interface board of the inverter. Therefore, it is recommended to choose an encoder whose shielding layer is not connected to the shell, and implement a point grounding at the far end, which can greatly improve the reliability of the system.
5. Reasonable selection of braking resistor
Braking resistor is used to consume the feedback electric energy generated by the elevator during power generation. The selection of the resistance value refers to the relevant content of the inverter manual and is selected with 100% braking torque. , but the power of the resistor is directly related to the size and price. Many manufacturers don’t know how to choose it. The resistors of the inverter with the same power are all the same. This is a serious hidden danger. Because the power of the resistor is related to the height of the floor, a 6-story building and a 30-story building, the frequency converter used may be 15KW, but the continuous operation time of the frequency converter is 5 times different, and the power also needs to be 5 times different. Only in this way can the reliability be guaranteed and the life of the resistor extended. Therefore, the power of the resistor should be calculated according to continuous braking first, and then the power should be adjusted accordingly according to different floor heights.
This paper aims at the content of traction machine, motor, frequency converter and operation debugging, etc., from two aspects of electrical and mechanical The effective countermeasures for the comfort during deceleration and deceleration stop operation have certain reference value for elevator manufacturers, traction machine manufacturers, and elevator renovation and maintenance manufacturers.