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Development of high-performance motorized spindle drive system

Abstract: This paper introduces a high-precision AC spindle speed regulation system. The system not only has high-precision dynamic and static speed regulation performance, but also has high-precision positioning function of repeated loading and unloading of hardness tester. It is widely used in high-speed CNC machine tools and machining centers

1 preface

motorized spindle is to install the motor directly in the spindle head, which reduces the mechanical speed change mechanisms such as pulley, gear or gearbox required by general spindle, improves the transmission efficiency, and connects the loose broach mechanism with the motorized spindle, so its structure is compact and realizes the so-called "zero transmission", which is generally used in machining centers, high-speed milling and other machine tools. For the electric spindle used in machining center, because it has an automatic tool change function more than ordinary machine tools, its control system must also have a high-precision positioning function to realize automatic tool setting, which puts forward higher requirements for the AC spindle drive system. In recent years, the domestic high-performance digital AC spindle drive system mainly depends on imports, which is expensive and difficult to maintain. Therefore, to develop a series of domestic AC spindle drive system with high technical performance and low price as soon as possible, in order to improve the performance of CNC machine tools, reduce costs, and improve the competitiveness of domestic CNC machine tools, is an important issue to be solved in the development of China's CNC machine tool industry. Therefore, we have developed a high-performance motorized spindle drive device

2 system structure

1) main circuit

the main circuit of the system adopts the common AC DC AC voltage source PWM inverter structure, as shown in Figure 1. The power switch adopts IPM (intelligentl power module) intelligent power module of Mitsubishi company. The power module integrates drive, short circuit, overheat and undervoltage protection, and simplifies the control circuit. The driving signal of IPM is PWM signal, which is generated by current hysteresis comparator and drives IPM action after dead time delay. The series reactor L in the bus makes the DC bus voltage stable; In order to realize fast braking, the corresponding pulse resistance braking circuit is set. When the bus voltage is higher than 650V, the power switch tube TZ is closed, and the system consumes mechanical energy on the resistance RZ to realize energy consumption braking

Figure 1 main circuit of the system

2) control system

the control system adopts dual CPU structure. Taking the 16 bit single chip microcomputer 80c196kc/20m of Intel company as the main CPU, and the programmable peripheral device zpsd411a2 constitute the basic system, which mainly undertakes the tasks of motor speed calculation, speed and position PID adjustment, vector transformation calculation and so on. The CPU is 89C51, which mainly realizes the panel monitoring and management, and completes the display of LED digital tube and indicator light, as well as the keyboard input processing function. The serial communication between the two CPUs is carried out by expanding an 8251. The communication interface adopts RS232 standard to ensure the remote monitoring within a certain range (50m). The speed and position detection circuit, digital and impulse input circuit, logic decoding circuit and dead time compensation circuit of power module all adopt large-scale logic gate array integrated circuit, which improves the reliability of the system. Its control power supply adopts switching power supply with good anti-interference performance to ensure that the structure is considered and optimized in terms of performance

3) interface circuit

in order to make the system debugging convenient and compatible with the CNC system interface signals produced by different manufacturers, various forms of interface circuits are also designed, mainly including: keyboard input; ± 10V analog input; 12 digit input; Pulse input and other speed input methods to meet the different needs of users as much as possible. In addition, in order to facilitate the communication with CNC, several level handshake signals are designed, such as zero speed arrival, positioning completion, system fault, etc. and relay output circuit

4) detection circuit

the detection link mainly includes the following two parts

current detection because CNC machine tools require a wide speed range, he said: "Hybrid electric vehicles and all electric vehicles have also brought challenges to the industry. The running speed of the motor is required to change from tens of thousands to tens of thousands of revolutions. Therefore, the frequency variation range of the output current is large, and the general current transformer can not meet the requirements. In addition, in order to obtain the fast current tracking performance of the system, the magnetic balance Hall current transformer is used to detect the output current. The measurement accuracy and linearity of the Hall current transformer are high, Wide frequency band and short response time. Because the three-phase winding adopts the Y-connection method, there is ia+ib+ic=o, and the three-phase current value can be known only by detecting any two-phase current. The actual current detected by the three-phase can be compared with the given current flow of the corresponding phase. Jinan Shijin's experiments on mechanics are increasingly in demand. After the over hysteresis comparator is used, the IPM power switch is driven to realize the three-phase voltage PWM modulation

speed and position detection because CNC machine tools require high speed control accuracy, the system adopts speed closed-loop control strategy. The system uses a 1024 high-resolution photoelectric pulse encoder to detect the feedback speed in real time. In order to improve the speed control accuracy, the photoelectric pulse encoder signal is shaped and processed by 4 times the frequency, and then enters the CPU to calculate the speed. The error between the given speed and the feedback speed is adjusted by the PI regulator to realize the speed closed-loop control. Because the rotation of the motor corresponds to 1024 pulses, the position of the motor rotor can be obtained by recording the pulses of the photoelectric encoder to achieve positioning control

5) protection function

in order to make the system work safely and reliably, it adopts multi-level protection such as overcurrent, short circuit, DC overvoltage, undervoltage, AC undervoltage, phase loss, device overheating, power on and power off, and has fault code display and memory function

over current protection not only uses the short-circuit over-current protection function of IPM intelligent module itself, but also adds a level of over-current protection in hardware to play a dual role

3 control strategy

for the high accuracy requirements of CNC machine tools, the control algorithm adopts the rotor field oriented vector control method. Using vector control technology, the AC motor is controlled by simulating the DC motor. Through coordinate transformation, the space vector of the AC motor stator current can be decomposed into two DC components oriented according to the rotor magnetic field, namely, the magnetic field current component IM and the torque current component IR, and these two components are controlled respectively, so as to obtain the same speed regulation performance as the DC motor. The constant flux control is adopted below the base speed, and the flux weakening control strategy is adopted above the base speed, so as to ensure the constant torque operation below the base speed and the constant power operation characteristics above the base speed that need to be met in the spindle processing process

the system adopts the strategy of current inner loop and speed outer loop to realize double closed-loop control; When the system needs high-precision positioning, a position closed loop is added outside the speed loop to realize the three loop control

4 Conclusion

the motorized spindle drive system makes full use of contemporary advanced microprocessor technology, power electronics technology, AC asynchronous motor vector control technology and automatic control theory. It can not only make the motor run smoothly and stably in the whole speed range, with low noise and vibration, but also has the main sleeve orientation control and other functions necessary for the machine tool. The driving control experiment of dzh5.5kw/7.5kw motorized spindle developed and produced by Luoyang Bearing Research Institute is carried out. The experimental results show that the system realizes the requirements of high-precision speed regulation and positioning, and has good dynamic and static performance. (end)