Speed regulation mode of hoisting mechanism of the

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Speed regulation mode of lifting mechanism of medium and large tower crane Abstract: This paper summarizes several main speed regulation modes of lifting mechanism of medium-sized tower crane in China, and points out the advantages and disadvantages of each mode and its scope of application. Especially for the DC speed regulation mode of French Potain large tower crane, combined with the national conditions, several ideas of speed regulation mode of large tonnage hoisting mechanism in China are put forward

key words: speed regulation mode of lifting mechanism differential double drive parallel

lifting mechanism is the most important transmission mechanism of tower crane. It requires low speed for heavy load, high speed for light load and wide speed regulation range. The advantages and disadvantages of the speed regulation mode of the hoisting mechanism directly affect the performance of the whole machine. Small and medium-sized tower cranes with a maximum lifting capacity of 4 ropes less than or equal to 6T have fierce competition and strict cost control. In China, multi speed motor pole changing speed regulation is mainly used. The scheme is simple and can still meet the work needs. Medium and large tower cranes of 8t and above need better speed regulation performance. There are many speed regulation modes. There are three selection principles: first, they should be stable and have small impact; Secondly, it should be economical and reliable, in line with national conditions; Third, it should be convenient for maintenance

1 at present, the main speed regulation mode of 8 ~ 12t hoisting mechanism in China

1.1 reducer with electromagnetic clutch shift and single speed wound rotor motor with eddy current braking

this speed regulation mode is widely used in Germany Liebherr tower crane, which has been used in China for decades, but now it has gradually faded out. It changes the speed ratio of the reducer by shifting the gear with the electromagnetic clutch, and obtains soft characteristics and slow positioning speed by the series resistance of the single speed wound rotor motor with eddy current braking. It has the advantages of stable specific efficiency and large speed regulation ratio. It has many disadvantages. Firstly, the electromagnetic clutch is generally made of domestic machine tools, which has short service life and poor reliability; Secondly, the clutch gear cannot be dynamically changed in the air, otherwise it will slide down, which is very dangerous; Third, the cost of reducer is high

if China can develop an economical electromagnetic clutch with long service life, it will still be a better speed regulation mode, and many users are used to using the electromagnetic clutch

1.2 common reducer plus multi speed wound rotor motor with eddy current braking

the idea of this method is to change the electromagnetic clutch shift of the previous method to multi speed motor driving common single speed ratio reducer

compared with the disadvantage of large shift impact of multi speed squirrel cage motor, the multi speed wound rotor motor with eddy current braking can obtain soft M-N characteristics by connecting resistance in series. The starting braking and gear switching are stable, with slow positioning speed (the positioning gear should not be operated for a long time). The power can be used more than that of squirrel cage motor, generally up to 55~75kw. This speed regulation mode has the advantages of simple structure, easy maintenance and high reliability. After repeated exploration, the motor supporting factory successfully solved the problem of heat dissipation of eddy current braking wound rotor motor a few years ago, greatly improving the reliability of this speed regulation mode

the electrical control of this speed regulation mode has become mature after years of application. The contactor produced in China by an international famous brand can fully meet the requirements, and the cost is declining. However, the wound motor above 75kW needs a large type of contactor, the demand for large contactors is small, and its price increases asymmetrically. Therefore, the large tonnage hoisting mechanism should find a way to reduce the specification of the contactor

at present, most 8 ~ 12t lifting mechanisms in China adopt this speed regulation mode. RCS lifting mechanism is actually this mode, but its structure is more complex. It has two winding motors and a more complex reducer. However, this kind of motor still has large peak current and impact during starting, braking and gear shifting, and the electrical control system is relatively complex. Generally, this speed regulation mode is not suitable for large tonnage hoisting mechanisms above 16t

1.3 differential planetary reducer plus double motors

the sun gear of the planetary reducer is driven by one motor, the planet carrier is driven by another motor through planetary reduction, and the inner gear ring of the outer track is fixed on the hoisting drum. This is the structure of differential planetary reducer

after the planetary system is determined as a suitable parameter, the drum speed depends on the speed and steering of the two motors, fast in the same direction and slow in the reverse direction. If it is a single speed motor, each motor has three states of forward rotation, reverse rotation and stop to match the other motor, so there are many speed gears. If a multi speed motor is used, there are more speed ranges (most can be discarded). This is the principle of differential speed regulation

the motor can be equipped with a squirrel cage or a combination of frequency conversion and squirrel cage. The small tonnage is equipped with a squirrel cage, and the large tonnage is equipped with a combination of frequency conversion and squirrel cage

this method has a large speed regulation ratio, can fully meet the requirements of heavy load, low speed, light load and high speed, and has high reliability. It is especially suitable for large tonnage hoisting mechanisms

however, the structure of the differential planetary reducer is complex. Generally, it needs non-standard design and can bring good assistance to measuring the comprehensive quality of the data. 1. When testing the tensile value of a certain data, the maximum pressure production of the data at the time when the data is about to be stretched to the fracture process should be measured. With dual motors, the cost is high and the control is complex. Not many mainframe manufacturers use it

1.4 variable frequency speed regulation

variable frequency speed regulation is the most advanced AC speed regulation mode today

with the gradual decline in the price of international frequency converters, frequency conversion speed regulation technology is more and more widely used. The domestic tower crane lifting mechanism has been used for many years with good effect, but it is not widely used

its advantages are that it can run for a long time at a slow positioning speed, realize zero speed braking, operate smoothly without impact, prolong the service life of the structure and transmission parts, greatly benefit the rope arrangement and service life of the steel wire rope, and improve the safety of the tower crane

with so many advantages, why is the use narrow? First, the imported frequency converter is still expensive, and the domestic frequency converter is not qualified; Second, once there is a problem with the frequency converter, it generally cannot be repaired. Most of them can only be replaced

due to the high cost of variable frequency speed regulation, the application of medium and small tonnage hoisting mechanism is generally less, while large tonnage is more. Variable speed regulation is widely used in small and medium tonnage, only waiting for the rise of domestic frequency converters

2 several optional speed regulation modes of large tonnage hoisting mechanism

20t and above the speed regulation mode of large tonnage hoisting mechanism is represented by French Potain. The DC speed regulation mode adopted by French Potain has good performance, but the price of tower crane is too high, which exceeds the general purchasing capacity in China and does not conform to China's national conditions

then, what speed regulation mode should be selected for the large tonnage lifting mechanism of tower crane to meet the national conditions? The author believes that there are several ways to choose from

2.1 variable frequency speed regulation

the larger the tonnage, the higher the stability requirements. Therefore, variable frequency speed regulation is the most ideal AC speed regulation mode for large tonnage hoisting mechanism. The problem is that high-power frequency converters are expensive. If the model of frequency converter can be reduced, the cost will be reduced. How to reduce the specification of frequency converter? The author believes that there are two methods

2.1.1 widening the constant power section

this method has been applied in the domestic tower crane industry, that is, the constant torque section is lowered from 50Hz to widen the constant power section. The result is to increase the speed regulation ratio of the motor and reduce the power

the speed ratio is increased, the heavy load speed is very low, and the light load or empty hook speed is very high, which fully meets the design requirements; The power is reduced, the specification of frequency converter is reduced, and the cost is reduced. The increase of speed regulation ratio did not improve the input speed of the reducer from a plastic machinery company in Qingdao with its newly developed wood plastic furniture board equipment. The noise level and the requirements for the reducer remained unchanged

2.1.2 two speed motor frequency conversion

the second method is the continuation of the first method. The frequency conversion of two speed motor (such as 4/8 pole) also increases the speed regulation ratio and reduces the power. If the first method of widening the constant power section is supplemented, the speed regulation ratio will be greater and the power reduction effect will be more obvious

2.2 double drive parallel connection of multi speed wound rotor motor with eddy current braking

it has been mentioned in previous 1.2 that wound rotor motor with eddy current braking should only be 55~75kw in general, and what should be done if 110KW is required for 20t lifting mechanism in Table 2, including changing one of the main products of the experimental machine? People will naturally think that the material has heat resistance and dimensional stability to double drive in parallel, that is, two sets of reduction motors and two sets of electronic controls are used to drive a drum together, as long as a certain reduction coefficient is considered

double drive parallel winch is not uncommon. We can divide the large into small and divide them into two. Mature and reliable reduction motors and electric controls with small tonnage can be used to facilitate production organization and spare parts service; In addition, when one set fails, another set can provide power for maintenance and halved hoisting operation, which improves the reliability of the hoisting mechanism

2.3 differential planetary reducer with double motors

as mentioned in the previous 1.3, this method is particularly suitable for large tonnage hoisting mechanism

3 conclusion

up to now, more than 95% of the domestic demand is for small and medium tower cranes of 2500knm and below. The vast majority of speed regulation methods adopt step-by-step speed regulation. Although stepless speed regulation is the development direction, it is still limited by cost and other aspects

the author has carefully calculated that the cost of variable frequency stepless speed regulation is about the same as that of multi speed wound rotor motor with eddy current braking, but the performance has been greatly improved by using the method of reducing the model of frequency converter as described above, which is of great significance

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