I. Introduction With the rapid development of China's economy, the elevator market is booming, with an annual demand of over 40,000 units, making it one of the most active markets in the world. Due to the significant influence of Japanese products on China's elevator industry, people's demands for elevator comfort are increasing. How to improve the comfort of elevator operation has become a crucial issue for elevator manufacturers. II. Selecting High-Quality and Stable Traction Machines The elevator control system is primarily a mechanical system. Elevator operation involves the reciprocating mechanical motion of the car on the guide rails. Due to its passenger-carrying function, it places stringent requirements on 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 entirely dependent on the installation of the guide rails 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 drive motor, and the variable frequency drive. The traction machine is the driving device for elevator operation, and its performance directly affects the comfort of elevator operation. The mechanical backlash of the traction machine primarily affects elevators during acceleration and deceleration. When the motor speed changes, the switching between electric and generator operation modes causes vibration, significantly impacting comfort. During S-curve acceleration and deceleration, there are typically one or two instances of noticeable weightlessness or overload, accompanied by abnormal noises from the traction machine. Additionally, in some retrofitted dual-speed elevators, the repeated high-speed/low-speed switching causes severe wear on the rubber gaskets in the connecting shaft, also leading to the aforementioned phenomenon. Therefore, elevator manufacturers must specify clear requirements for the backlash of newly selected traction machines and regularly inspect the wear of the connecting shaft during maintenance. Furthermore, poor machining and installation precision, or inadequate dynamic balance adjustment of the internal gears or worm gears of the traction machine can also cause vibration and noise at high speeds. In one instance, at a manufacturer, I discovered an elevator with exceptionally high vertical vibration. After trying everything to no avail, I suspected a problem with the traction machine. The manufacturer didn't believe me and replaced all brands of inverters available on the market without improvement. Replacing the traction machine resolved the issue. The problem was that the traction machine manufacturer was small-scale, with outdated testing methods, resulting in inconsistent traction machines and causing significant direct and indirect losses to the elevator manufacturer. Therefore, when choosing a traction machine, one should not prioritize price; it is essential to select a manufacturer with strong technical capabilities, comprehensive testing methods, and a sound quality assurance system. Another point to emphasize is that, at the same elevator speed, it is better to choose a traction machine with a larger reduction ratio. A larger reduction ratio results in less backslip, making it easier to adjust the starting comfort. Practice has shown that, at the same elevator speed, a traction machine using a 6-pole motor has a worse starting comfort than one using a 4-pole motor. The fundamental reason is that the starting torque of a 6-pole motor is not more than 1.5 times greater than that of a 4-pole motor. III. Selecting a High-Quality Drive Motor While ensuring the quality of the traction machine, the performance of the motor配套 with it directly affects the performance of the elevator's starting and braking processes, primarily manifesting as a difference in starting comfort. If the motor has a large starting torque, the backslip at the moment the elevator releases the brake will be minimal. Currently, many inverter manuals contain seriously misleading statements. While frequency converters can achieve starting torque increases of 200% or even 300%, this is practically meaningless. If a motor's designed starting torque and maximum torque are low, even the best frequency converter will not produce a large output torque and is prone to speed fluctuations, causing oscillations. Based on the basic knowledge of asynchronous motors, the MN curve of the motor is shown in Figure 1(a), where point A 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 motor's slip s. A larger slip results in a larger initial starting torque. To increase slip, a larger rotor resistance and a smaller rotor inductance are required. Figure 1(b) shows the mechanical characteristic curves under different rotor resistance conditions. It can also be seen from the figure that as the rotor resistance increases, the maximum torque remains unchanged, but the corresponding maximum slip increases. Under the same load, the slip also increases. This is why imported brand elevators use high-slip motors. However, many imported brand traction machines are currently equipped with domestically produced low-slip motors to reduce costs, with slip frequencies generally less than 2.5Hz, significantly reducing their starting performance. Therefore, when choosing a traction machine brand, the brand and performance of its matching motor are equally important. [align=center][IMG= Asynchronous Motor Mechanical Characteristics]/uploadpic/THESIS/2008/1/2008012512061188668P.jpg[/IMG] (a) Mechanical characteristics (b) Mechanical characteristics under different rotor resistances Figure 1 Asynchronous Motor Mechanical Characteristics[/align] IV. Selecting a High-Performance Inverter Asynchronous motor vector control is based entirely on motor parameter vector control, therefore the motor parameters must be able to learn automatically. Otherwise, superior performance cannot be achieved. Therefore, firstly, an inverter capable of self-learning motor parameters must be selected. Secondly, the inverter must have a torque output of more than 150% at zero speed to ensure good starting and stopping comfort. In addition, it needs very good overload capacity, 110% of the rated load, and must run continuously, especially for high-rise elevators that need to run at full load for more than 30 seconds, this point must be considered even more. Some foreign manufacturers' frequency converters cannot operate continuously for 60 seconds at 100% rated load. Therefore, when used for high-rise elevator control, it is generally recommended to use them at a higher speed, causing unnecessary economic losses for users. After selecting a frequency converter, to achieve a better user experience, it is crucial to properly adjust the converter's performance and operating curves. During elevator startup, the mechanical guide shoes have significant static friction, which can be eliminated by adjusting the starting speed and the starting speed holding time. Additionally, most frequency converters have a speed loop PI parameter adjustment function. By adjusting the speed loop PI parameter, the dynamic response speed and speed stability of the frequency converter can be effectively adjusted, improving the comfort of elevator startup and steady-state operation. Starting performance is related to the low-frequency PI parameter. You can initially set the low-frequency I to zero or a relatively large value, and adjust KP without considering leveling accuracy. Increasing KP speeds up the low-frequency dynamic response and increases the starting torque, but excessively large KP can easily cause oscillation, worsening the comfort of startup and stopping/creeping. Therefore, KP must be increased to the point where the elevator does not oscillate under full load and no load conditions, which is the critical threshold. Then, the I parameter can be gradually decreased to achieve satisfactory results in both starting and creeping. The principle of high-frequency PI parameter adjustment is to ensure that the overshoot during starting acceleration and stopping deceleration is minimized, generally less than 2% of the rated speed, while ensuring speed accuracy under steady-state conditions, generally not exceeding 0.001m/s. First, set the high-frequency I to zero or a relatively large value, adjust K to make the parameter less than the critical parameter for the elevator to oscillate in high-frequency steady state, and then gradually decrease I until the overshoot meets the required index. For situations using the same traction machine and machinery, the parameters can be copied via keyboard after adjusting one elevator. In the above, the unit of the integral time constant I is time unit s. It is particularly important to note that most frequency converters on the market currently use two independent numbers to adjust the PI parameters, without the concept of an actual physical quantity. In this case, the larger the I, the smaller the time constant. The comfort during acceleration and deceleration should be addressed through S-curve adjustment. Generally, acceleration and deceleration are between 0.5 and 1. For rapid acceleration at the beginning and rapid deceleration at the end, the values ​​can be adjusted to 0.25 to 0.5, and for rapid acceleration at the end and rapid deceleration at the beginning, they can be between 0.5 and 0.9. The adjustment of the S-curve also depends on the elevator's location. For places with high comfort requirements, such as hospitals and nursing homes, the corresponding parameters need to be reduced. For places with high efficiency requirements, such as office buildings, the corresponding parameters can be appropriately increased. Increasing the values ​​for rapid acceleration at the end and rapid deceleration at the beginning helps to overcome the jitter caused by gaps during acceleration and deceleration. V. Using the Optimal Control Sequence The optimal control sequence is shown in Figure 2. After receiving the run command, the inverter first enters the zero-speed running process, with a delay of T1 to ensure the motor excitation reaches a steady state before opening the alarm. Simultaneously, the inverter starts running at the starting speed. After a starting speed holding time T2, it runs from high speed to low speed to zero speed. After zero-speed running T3, the alarm is closed while ensuring zero inertial influence. Since the alarm requires a certain amount of time to engage, the run command must be cancelled after a delay of T4. Following this sequence ensures ideal comfort during both starting and stopping. In the TD3100 frequency converter, T1 is set by F7.00, T2 by F3.01, T3 by F7.01, and T4 is determined by the controller. If the controller delay time is insufficient, the TD3100 frequency converter will automatically extend the command hold time. [align=center][IMG=Ideal Control Timing Diagram for Elevator Control]/uploadpic/THESIS/2008/1/2008012512061657653O.jpg[/IMG] Figure 2 Ideal Control Timing Diagram for Elevator Control[/align] VI. Other 1. Starting Compensation For low- and medium-speed elevators below 1.75 m/s, due to the low operating speed, starting compensation is generally not required to achieve a satisfactory level. For medium- and high-speed elevators above 1.75 m/s, if a high level of starting comfort is required, a weighing device must be added to compensate for the starting torque. There are generally two types of weighing devices: switch detection and analog detection. Switching quantity detection is low-cost, but it only provides stepped compensation. Typically, four switches are installed, allowing accurate compensation at any four points between no-load and full-load conditions. However, because it's stepped compensation, it doesn't achieve ideal results. Analog sensors can achieve stepless compensation, but the problem is that their output often shifts with elevator use, causing compensation errors. Sometimes the effect is worse than no compensation, so the compensation gain needs to be adjusted periodically. The starting torque compensation principle of the TD3100 elevator-specific frequency converter is shown in Figure 3. [align=center][IMG=TD3100 elevator-specific frequency converter starting torque compensation principle]/uploadpic/THESIS/2008/1/2008012512062271579P.jpg[/IMG] Figure 3 TD3100 elevator-specific frequency converter starting torque compensation principle[/align] 2. Proper selection of vibration dampers and wire ropes: Many elevator manufacturers are very arbitrary in their selection of vibration dampers. In fact, vibration dampers play a very important role in improving elevator comfort. Vibration dampers generally come in three types: rubber damping pads on the traction machine base, damping springs or rubber damping pads at the bottom of the car, and wire rope vibration dampers at the top of the car. The quality and damping effect of the damping pads on the traction machine base vary greatly, directly affecting elevator comfort, especially when the elevator starts and stops at the top 2 to 4 floors. The quality of the vibration dampers at the bottom of the car directly affects the smoothness of the elevator's steady-state operation. If the elastic coefficient is too high and the characteristics are too stiff, it will not provide damping and will generate high-frequency vibrations, causing a numb feeling in the legs. In severe cases, it will cause high-frequency vibrations in the car, generating significant noise. Conversely, it will generate low-frequency oscillations, causing a sinking sensation. Therefore, proper selection is essential. The damping effect of the wire rope is the same as that of the vibration dampers at the bottom of the car. The appropriate wire rope with a suitable elastic coefficient must be selected based on the floor height to ensure good damping effect while maintaining the required extension and contraction under full load. In addition, in high-rise elevators, due to the long length of the wire rope and inconsistent tension, the wire rope is prone to swaying and colliding during high-speed operation, causing vibration of the car. An effective method is to add a wire rope vibration damper to the end of the wire rope to effectively absorb the vibration waves and prevent reflection that could cause beat phenomena. 3. Proper selection of encoders. The encoder is an essential component of the elevator inverter's closed-loop system, and its proper selection has a significant impact on the safe and reliable operation of the elevator. In terms of installation, the bushing type is more reliable, but it is slightly more expensive than the coupling type. Currently, many manufacturers using coupling type encoders use very simple connection methods because standard couplings are prone to breakage when the coaxiality is poor, resulting in very poor reliability, thus creating safety hazards for elevator operation. In terms of wiring, there are push-pull output and open-collector output types. It is recommended to use open-collector encoders when the encoder wiring exceeds 5m to improve anti-interference capabilities. An encoder pulse count of 300 pulses per revolution is generally sufficient to ensure the normal operation of the frequency converter. It is recommended, if cost permits, to increase the encoder pulse count to 1000 to 2000 pulses per revolution, which can significantly improve the elevator's starting comfort. This is because a higher pulse count makes it easier to quickly detect runaway during startup, thereby achieving rapid torque adjustment and reducing runaway. 4. Proper Grounding of the Control System: Grounding is a critical issue affecting reliability in elevator control systems. Due to the non-standard power supply in my country, most systems use three-phase four-wire rather than three-phase five-wire, making grounding issues more prominent. During installation and commissioning, it is essential to first ensure that the control cabinet, traction machine, and car are reliably grounded or neutral, and then the encoder must be grounded. However, it must be emphasized that the standardization of encoders on the market is currently poor. Some encoders have poor anti-interference capabilities, and some manufacturers connect the encoder lead shielding layer to the encoder housing, which is a very serious error. If the user connects the encoder shield to the inverter's ground, a potential difference exists between the inverter and the motor due to the grounding at both ends, which can easily cause interference. This can range from minor issues like low-frequency vibration and random overcurrent protection activation in the elevator, to more serious problems like motor leakage causing severe damage to the inverter's interface board if the traction machine is not grounded or has poor grounding during commissioning. Therefore, it is recommended to use an encoder whose shield is not connected to the casing and to implement remote single-point grounding, which can greatly improve system reliability. 5. Proper Selection of Braking Resistor: The braking resistor is used to dissipate the feedback energy generated during the elevator's power generation process. The resistor value should be selected based on the inverter's manual, using 100% braking torque. However, the resistor's power rating directly affects its size and price, and many manufacturers are unsure how to select it, using the same resistor for inverters of the same power rating. This poses a serious safety hazard. The resistor's power rating is related to the building height. A 6-story building and a 30-story building might both use 15kW inverters, but the continuous power generation time of the inverters differs by a factor of five. Therefore, their power ratings also need to differ by a factor of five to ensure reliability and extend the resistor's lifespan. Therefore, the power of the resistor should first be calculated based on continuous braking, and then the power should be adjusted accordingly based on different floor heights. VII. Conclusion This article addresses the traction machine, motor, frequency converter, and operation debugging, proposing effective countermeasures from both electrical and mechanical perspectives to improve the comfort of elevators during start-up, acceleration, steady-state operation, and deceleration and stopping. These measures offer valuable reference for elevator manufacturers, traction machine manufacturers, and elevator renovation and maintenance companies.