Crane belongs to a kind of lifting machinery, is a kind of cycling, intermittent movement of machinery. A working cycle consists of lifting the object from the place where it is retrieved, then moving horizontally to the point where it is lowered, and then moving in reverse to return the object to its original position for the next cycle. Generally, hoisting machinery is composed of lifting mechanism (making the articles move up and down), operating mechanism (making the articles move), luffing mechanism and turning mechanism (making the articles move horizontally), plus metal mechanism, power plant, control and necessary auxiliary devices. The hoisting machinery used in the bridge construction project, according to the different structure and performance, can be divided into three categories: light and small crane equipment, bridge type crane and boom type crane. Multi-action lifting machinery for lifting heavy objects vertically and horizontally within a certain range. Also known as a crane. Belongs to material handling machinery. The working characteristic of crane is to do intermittent movement, that is, in a working cycle, the corresponding mechanism of taking materials, migration, unloading and other actions is working alternately.

The crane frequency conversion speed regulation system is given by the main control controller or potentiometer as input, and is used in combination with the frequency conversion frequency modulation speed regulation electronic control equipment, load measurement and control instrument, limit switch and brake to control the hoist hoist and other ac frequency conversion asynchronous motor hoisting, braking, reversible operation and speed regulation.

Equipment selection parameters: 2 multiplier of movable pulley, 18.5kw 4-pole asynchronous squirrel cage motor with lifting mechanism, speed ratio of reducer I=31.5; The diameter of the drum is 300mm, that is, I=31.5,R=D/2=150mm=0.15m,

Nn=1450 RPM,Pn= 18.5kw.

1) calculation of lifting weight:

Pn = 2 * PI * Tn/Nn * 60 * 1000

: Tn = Pn 60/2 * PI * * 1000 * Nn = 18.5 * 1450 * 1000 * 60/2 PI = 121.9 Nm

The theoretical lifting weight is:

F=2*Tn*I*/R*10000=2*121.9*31.5/0.15*10000=5.1198

Then the lifting weight is:

Fmax=0.64*F=0.64*5.1198= 3.28t has a safety factor of 1.1 times compared with the required lifting weight, which basically meets the requirements.

2) calculation of lifting speed:

Vmax = D * Nn / 2 * PI * I = PI 1450/2 * * 0.3 * 31.5 = 21.7 m/min

According to the above formula, the lifting speed of the motor decreases a lot under the frequency conversion mode, which is mainly to consider the cost saving and competitiveness in the market, and to optimize the related hardware cost at design time. Through various coordination methods, such as shortening start-up and positioning time, and running with an empty hook above 50HZ, the speed reduction is not obvious in practice.

AMB300 inverter introduction:

AMB300 series frequency converter is a new generation of high performance frequency converter which represents the future development direction of frequency converter. Compared with the traditional sense of the inverter, in meet customers' different performance and functional requirements, it is not done by multiple series of products (and thus additional manufacturing, sales, operation and maintenance costs), but in customer demand, on the basis of reasonable segmentation, carries on the modular design, through a single series of module combination, to create a custom tailored platform. It is one of the few domestic frequency converters with magnetic flux vector technology. This series of frequency converter adopts the excellent non-velocity vector control strategy to make it have the fast dynamic response, the advanced current limit technology and the hardware optimization design, can guarantee in the case of frequent fluctuation of load, the frequency converter does not trip. And has the following characteristics:

1) the reliability

Perfect reliability design scheme: such as redundancy design, reduction design, all components are industrial or military grade; Professional production platform, so as to ensure the reliability of the whole machine.

2) soft start

Compared with the power-frequency starting mode, the use of frequency converter control can reduce the mechanical part of the vibration and the impact of the false for the user to save the cost of maintenance, stable operation.

3) high starting torque

High performance magnetic flux vector control mode, low frequency band provides stable high output torque.

    The advanced modern ac frequency conversion technology is adopted to carry out technical transformation on the tower crane electric driving system, so that the crane can achieve smooth operation, improve operating efficiency, improve overload operation, eliminate the starting brake impact, reduce electrical maintenance, reduce power consumption, improve the power factor and so on. At the same time, it also has over current, over voltage, under voltage and input phase fault protection, as well as inverter overtemperature, overload, overspeed, brake unit overheating, I/O fault protection, motor fault protection and so on.

1) wide range of speed regulation can realize the operation required by control and positioning;

2) the functions of soft start and soft stop reduce the impact of mechanical transmission, significantly improve the bearing performance of the steel structure, and extend the service life of the crane;

3) high integration components and high reliability low-voltage electrical appliances, effectively solve the complex wiring problems of the original electrical system, not only reduce the probability of system failure, but also easy to maintain;

4) at zero speed, the motor can be output at full torque. Even if the brake is loose or fails, the weight will not slide, ensuring the safety and reliability of the system;

5) it has fast dynamic response, no slip hook and truly realizes the function of "zero speed crossover";

6) the special load weight measuring and controlling instrument is equipped with the corresponding software, and the lifting speed can be switched automatically with the change of load weight, so as to achieve the operation requirements of "fast under light load, slow under heavy load";

7) the frequency converter used in the system, with automatic energy-saving operation mode, can greatly improve the power factor of the system and the whole machine work efficiency, the energy saving effect is significant, the average power saving rate can reach more than 20%;

At present, most tower cranes adopt stepless speed regulation, stepless speed regulation is the development direction, but it is still limited by cost and other aspects. The author has done the calculation, as mentioned above does not increase the type of frequency converter, appropriate sacrifice of speed method, the cost of variable frequency stepless speed regulation and with eddy current braking multi-speed wound rotor motor variable pole speed regulation gap is not big, performance has been greatly improved, it is of great significance.