Working principle of spindle drive system of machining center
From the description of the characteristics and development trend of the spindle drive system of CNC machine tools in Chapter 1, we know that AC variable frequency or AC servo electric spindle control system is commonly used for spindle V motion at present. The machining center has high requirements on the control of the spindle. It needs to realize the wide range stepless speed change, and it also needs to realize the fixed angle stop (i.e. accurate stop) when the cutter is automatically replaced. The quasi stop of the spindle can be realized in many ways. The AC servo electric spindle has the quasi stop function, and its own PLC module and PMC module of CNC can coordinate to achieve the quasi stop of the spindle. PMC only sends the quasi stop command, and the spindle drive system can complete the quasi stop action; The AC variable frequency motorized spindle has only speed regulation function but no accurate stop function. At this time, an accurate stop sensor should be installed on the spindle and PMC program of CNC system should be used PMC software controls the quasi stop speed and in place stop of the spindle system. After the quasi stop, the spindle is restored to the standby state. The control accuracy of AC servo electric spindle is far higher than that of variable frequency electric spindle. The control principle is also more complex. It is highlighted here
1、 Working principle of spindle drive system of machining center
The spindle motor of CNC machine tool is cage induction motor because of its high dynamic power In order to check the speed or position of spindle 9, a rotary encoder must be installed outside the spindle or a built-in encoder must be used. The closed loop control and vector operation of the spindle drive unit are realized by the internal computer control system. The principle block diagram of the spindle drive unit is shown in Figure 3-6; V - The CNC system sends a speed command to the spindle drive unit. The drive unit measures the command with the rotary encoder
Actual speed U By comparison, the current desired torque U7 and the desired flux vector Uy of the rotor are calculated by the digital speed regulator ASR and the flux counting generator, and then ej the actual torque and the flux calculation results U7U, y2fll respectively After the calculation of torque and flux regulator, the learned current component ui: l and excitation current component UL of the equivalent DC motor (two-phase rotating shaft system) are obtained, and then enter the two-phase stationary shaft system through reverse rotation vector transformation. Finally, they enter the three-phase stationary shaft system through 2'3 under transformation The desired three-phase stator current of the frequency converter is obtained. By controlling the SPWM actuator and IGBT frequency conversion main circuit to make the three-phase load current follow the desired value, the speed closed-loop control of the spindle can be completed
H400 machining center uses Mitsubishi MIIS-A-SPIA series AC spindle "Ipi. Actuator. It adopts current type under quantity control mode and SPWM waveform. It can accept digital speed setting or analog speed setting. It has monitoring and diagnostic functions for overcurrent, overvoltage, overload, undervoltage, overheating, overspeed and other multiple protections. The communication function set by the system can be used to set the quasi stop parameters and operation parameters through a PC. The controller does not actually accept the quasi stop positioning of the main shaft
CNC speed command. Only complete the position closed-loop control according to the preset quasi stop position, quasi stop speed and other parameters
In fact, it is difficult to solve the problem of whether a three-axis CNC machining center is better or a four-axis machining center is better. There is only a problem that is not suitable for machining some kinds of parts. Basically, all three-axis machining centers can process the parts that can be processed by a four axis machining center, while the parts that can be processed by a four axis machining center may not be processed by a three-axis machining center.
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