The gantry milling machine is a machining equipment for processing larger workpieces, and its electrical control system includes two parts: the main transmission of the workbench and the logical control of the feed organization. Henan Jiaozuo Maike Company has a gantry milling machine, which has been used for many years since the 70s. The main drive of the workbench of the gantry milling machine adopts the DC reversible speed regulation drag method. The early DC speed control system was composed of discrete components, and after several years of use, the fault rate increased significantly, the amount of repair work continued to increase, and the number of fault strike hours increased sharply, which has severely affected the normal progress of production. The original DC speed regulation system has been eliminated, and it is not possible to replace the DC speed regulation system, and it is inevitable to carry out technical transformation.
First, the transformation plan
For the transformation of the DC speed regulation system, if the DC motor is retained, the speed regulation system can use the digital thyristor DC speed regulation system. The advantage of this plan is that the original DC motor is used, which is more economically economical, but the defect is also obvious, and the defect is that the DC motor is more than the maintenance work of the asynchronous squirrel cage motor, especially the DC motor that has been used for many years, the commutator is worn severely, and the repair cost is more. Another plan is to choose the communication speed control system, replace the main drive DC motor with a communication asynchronous squirrel cage motor, and use a frequency converter for the speed control system. The disadvantage of this plan is that in addition to the demand for frequency converters, it is also necessary to replace the DC motor with a communication motor, and the cost of transformation is relatively high. However, the structure of the communication motor is simple, the maintenance is small, and the inverter function is excellent, which is convenient for completing the optimal control. After comparing the good and bad of the two plans, choose the transformation plan that uses communication to regulate the speed.
Second, the frequency conversion transformation of the gantry milling machine
1. Selection of frequency converter and accounting of capacity
The selection of the inverter should be based on the capacity of the communication motor, and the selection of the capacity of the communication motor should be based on the DC motor. The parameters of the DC motor of the original working table are: PN=18.5kW, nN=1000r/min, and the corresponding communication motor PN=18.5kW, nN=970r/min. Gantry milling machine often works in a low-speed machining state, in order to ensure the processing quality, the motor is required to have a large torque at low speed. Considering the mechanical characteristics of the communication motor, the capacity should be appropriately increased when selecting the communication motor. In this example, the communication motor was selected as a 22kW 6-pole squirrel cage motor.
The SB61G+ inverter produced by Expectation Sunland Technology Co., Ltd. is selected. Considering that the return stroke time of the milling machine table is relatively short, the inertia is large, and the braking unit and braking resistor are required, and the braking resistor is equipped with 30Ω and 5kW according to the specification of 100% braking torque, and considering that the braking is more frequent, the capacity of the resistance is appropriately increased to 10kW.
2. The setting of the function of the inverter
From the operation process of the gantry milling machine platform, it can be seen that the operation speed of the operation table has 4 stages, namely N1, N2, N3 and return operation speed. The SB61G+22KW inverter is a multi-stage speed control method, and the multi-stage frequency control input terminals of the inverter are X1, X2, X3, X4; The frequency value of multi-stage speed is determined by the workpiece processed, and the moment of acceleration and deceleration is determined by the function code F009, F010, F631-F636, and its control signal is taken from the non-contact switch of the milling machine, as long as the milling machine table moves to the corresponding direction, the output signal of the non-contact switch is sent to the corresponding input port of the inverter, and the inverter will speed up, decelerate, reverse or run at a constant speed.
3. The use of PLC
Due to the aging of the control circuit and low-voltage components, the control circuit of the milling machine is transformed while the main drive frequency conversion speed regulation of the gantry milling machine working platform is transformed. The use of PLC can greatly reduce the clutter of the control circuit and reduce the cost. The PLC uses HOLLIAS-LEC G3 40-point PLC, and the programming method is a ladder diagram, which is not very messy and will not be repeated.
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