PLC and inverter in the application of bridge crane transformation system

Abstract: the author analyzes the control requirement of the bridge crane, in view of the traditional causes of bridge crane, this paper introduces the use of frequency converter in combination with PLC to modify its feasibility and implementation method. 1 the introduction with the development of industrial automation, PLC, frequency converter has been widely applied in the factory equipment modification. Bridge crane, due to the working environment is poor, and reload the frequent starting and braking, reverse, speed and other operations, also requires a certain speed range, so the traditional relay control and series resistance speed has presented many shortcomings, for this kind of production machinery is very necessary. 2 original equipment basic situation of coking workshop of a petrochemical refinery grab bridge crane is used for petroleum coke yards, petroleum coke from the ground to catch in the park nearby on the train. Bridge crane electrical transmission of cart machine 2 sets, 1 car motor, grab motor 1, hoisting motor 1, are the winding type ac motor, using the method of rotor resistance starting and speed regulation. Due to poor working conditions, dust and harmful gas on the motor slip rings, carbon brush and 21 contactor corrosion is larger, and heavy task, to guarantee the operation procedure impact current is big, contactor eroded seriously, carbon brush in a blaze, motor and rotor winding string of resistance loss, the fracture failure occurs frequently, average 2 larger fault occurring on a monthly basis. Five times, a larger impact on production. Soft speed rotor resistance, mechanical properties, the load changes, also changes in the speed, the control effect is poor, the series resistor fever for a long time, the power waste, low efficiency, so to fundamentally solve the problem of bridge crane high failure rate, only using PLC as a control device, and thoroughly change the wound rotor motor series resistance speed control mode. 3 after transforming system basic situation of 3. 1 in the modern industrial control, the system of PLC with high reliability, strong anti-interference ability, strong adaptability, flexible application, programming is convenient, easy to use, control system design, installation, commissioning, maintenance convenience, less maintenance work and so on a series of advantages and has been widely used, because this system is mainly some logic control, so taking PLC as control core, the input of the whole system of 26 points, output point 27 points, mitsubishi FX2N - optional 64 Mr, this model is the fastest strongest function in the PX series PLC controller, it has 32 input point, output points, 32 built-in user memory is 8 k steps, the principle diagram of the system composition, such as chart 1. Figure 1 the principle diagram of the system for bridge crane grab the opening and closing, ascending, cart, trolley type motor with four sets of FRNIC5000G7 converter drag; To grab the opening and closing of motor, promotion of 45 kw from 30 kw instead of wound rotor motor squirrel-cage motor, cart car motor unchanged, but will lead to convey his son winding short-circuit, remove the carbon brush and slip ring; To make work safe and reliable, to prevent due to power outages, brake unit converter tripping or failure caused by lifting objects under hit appear dangerous, still retain original mechanical brake braking device. 3. 2 speed control system with the working condition of bridge crane in the motor load for constant torque load, grab opening-closing, cart, trolley motor runs in quadrant 1, 3, are electric state, hoisting motor can run in quadrant 1, 3, 4, adopts frequency control of motor speed, mechanical change especially hard, when the load torque changes, motor speed basically remain unchanged. Bridge crane's speed regulation can use frequency selection function of multilevel inverter, transfer FWD, CM on is, REV, CM through inversion, the X1, CM, X2, CM, X3, CM three pairs of terminal connected respectively, or to switch on at the same time, two or three available 7 kinds of frequency, thus can easily get bridge crane required by the positive and negative two direction each 6 kinds of speed. To the requirements of the field staff, to take care of operation habit, bridge crane speed control is still using the original primary controller and CAM controller. With five main controller for contact, to get the inverter output of 6 kinds of speed. Setting of motor deceleration time by frequency converter to change. 3. Three PLC control wiring and program design of the whole system, four five electric motor frequency converter, PLC input and output points more, the connection condition of frequency converter and PLC controller, to illustrate this, in this only to grab the inverter and the PLC connection as an example, illustrates its working condition. A part of the system of PLC controller I/O distribution as shown in table 1. Table 1 part of PLC I/O allocation table and the promotion of the connection of the motor inverter situation such as chart 2. Figure 2 motor frequency converter and PLC connection because of the five motors in the system ( The M3, M4 is the parallel running, two control conditions are exactly the same) The operation of the main controlled by input directly, so the design of the system of ladder diagram program can according to each input and motor run relationship experience method is used to design, use of guaranteed power directly by the input signals from the motor and brake electromagnet the gain and loss of electricity, programming is simple, in this not introduced in detail.
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