Technology and application of electro-hydraulic se

2022-08-03
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Technology and application of electro-hydraulic servo system for injection molding (II)

the insufficient range of power speed regulation is a limitation of permanent magnet motor. Using the experience of electric vehicle motor system for reference, the company adopts the structure of permanent magnet reluctance synchronous motor, which effectively breaks through this limitation and can fully meet the requirements of injection molding electro-hydraulic servo application

motor rotor position/speed sensor

to control the torque and speed of the servo motor, it is necessary to detect the position and speed of the motor rotor. Most servo motors use photoelectric encoders as position/speed sensors with a year-on-year increase of 717%. The advantages of photoelectric coding disk are simple structure and easy to obtain high precision. However, due to the fact that its processing circuit must be integrated with the motor, in the environment of high motor temperature and large vibration, coupled with electromagnetic interference, its electronic circuit often fails to work normally, resulting in code loss, resulting in disordered control of the motor and even damage to the motor

the Regal servo system uses a high-performance rotary transformer that meets the requirements of electric vehicles as the speed feedback component. It has a firm structure and strong resistance to high temperature, vibration and interference. It ensures that the system can work stably and reliably in the harsh environment of the injection molding machine, and the accuracy can reach 4096 pulses per revolution

servo drive controller

the servo drive controls the current, torque and speed of the servo motor according to the pressure and flow instructions of the injection molding machine controller (upper computer). Regal servo driver includes servo control, rectifier/inverter power, communication interface, feedback detection and other units. The rectifier/inverter power unit adopts advanced integrated IGBT module; The servo control unit includes position controller, speed controller, torque and current controller, etc. The high-speed digital signal processor (DSP) is used as the control core of the driver to realize various complex control algorithms, and output pulse width modulation (PWM) signals to the inverter power drive circuit to change the output power of the inverter, so as to achieve the purpose of controlling the three-phase permanent magnet synchronous AC servo motor

oil pump

as the main power source of the injection molding machine, the good matching between the oil pump and the servo system is very important to its overall performance and energy saving effect. At present, the oil pumps applicable to the servo system include gear pump, column plug pump and screw pump, with different characteristics. Therefore, the servo system should be able to adapt to various oil pumps and optimize parameter settings. Yuneng servo system has advanced load parameter identification function, which can flexibly optimize and adapt to various oil pumps

pressure feedback component pressure sensor

the pressure closed-loop control strategy is adopted by the Regal servo system, that is, the oil pressure of the injection molding machine is adjusted by controlling the motor torque and speed to follow the pressure command value. The oil pressure signal is obtained through the pressure sensor, and its accuracy will determine the control accuracy of the injection molding machine pressure. Regal can provide pressure sensors with different control accuracy requirements

field oriented control technology

the basic principle of field oriented control (vector control) is to simulate the torque control law of DC motor on three-phase permanent magnet synchronous motor. On the field oriented coordinate, the current vector component is decomposed into the excitation current component that generates magnetic flux and the torque current component that generates torque. The two components are perpendicular to each other, independent of each other, and then adjusted respectively. The vector control of AC motor decouples the control of torque and magnetic flux. When controlling torque, it does not affect the size of magnetic flux, and when controlling magnetic flux, it does not affect torque. It makes AC motor control as convenient as DC motor control, and can obtain dynamic characteristics comparable to DC speed regulation system

in order to maintain the maximum output torque of the motor all the time, the system needs to obtain the instantaneous position and speed of the motor rotor. Through coordinate transformation, the measurable stator variables are transformed into the coordinate system with good flexibility of the rotor, so as to form a current closed loop, dynamically track the change of the current, and then use the speed sensor to form a speed closed loop. Finally, the double closed loops of current and speed are realized to obtain excellent system stability Fast response and control accuracy. These complex operations need the help of the high-speed digital Jinan experimental machine factory Jinan new era Gold Testing Instrument Co., Ltd. data remains unchanged. You are welcome to visit our experimental machine word signal processing chip DSP to realize

Another advantage of

field oriented control is that the copper loss and iron loss of the motor are optimally distributed through the separate control of torque current component and magnetic flux current component, so as to obtain the best system efficiency

control principle and algorithm of electro-hydraulic servo system

Figure 2 block diagram of electro-hydraulic servo control system

in combination with figure 2 and system structure, the system control principle is briefly described as follows: receive the flow and pressure given signals from the main control board of the injection molding machine in real time; Instantly detect and feed back the pressure from the oil pump and the speed from the motor

for the error between given and feedback, the high-speed DSP of the servo driver uses various control algorithms to generate control signals for the servo motor, and drives the servo motor through the IGBT module to realize the double closed-loop control of pressure and speed. (to be continued)

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