Study On Differential Cylinder System Controlled With Variable Speed Pump And Technology Of Low-energy Injection Mokling Machine

Injection molding machine is a complex system including mechanic, electric and hydraulic. In the manufacturing process of plastic products, system has some shortcomings of noise, high energy consumption, low efficiency and poor control. It is an urgent requirement to develop a kind of low-energy, high-performance injection molding machine. This thesis is supported by national natural science foundation of China'Theory and method of differential cylinder servo system controlled with new flow balance pump'and Shanxi Province scientific and technological project'Novel efficient and energy saving plastic injection molding machine hybrid controlled by mechanical and electro-hydraulic technology'. Differential cylinder system controlled with variable speed pump and technology of low-energy injection molding machine are studied. It is a useful exploration to improve injection molding machine performance.Aims at speed characteristics of permanent magnet synchronous motor (PMSM) as hydraulic system power source, the dissertation analyzes coordination control importance of driving and controlling circuit. Voltage space vector pulse width modulation is studied for harmonic and harmonic loss caused by nonlinear power switches in drive circuit. Reasonable choice of zero vector position and the switch frequency are to reduce loss and improve efficiency. On the basis vector decoupling control of PMSM is done. Through modeling and decoupling of PMSM in accordance with the rotor oriented field, current and speed regulators are designed. Simulation and test verify that coordination control improves system performance.To solve the differential cylinder volumetric flow rate caused by piston area ratio, new flow distribution windows displacement pump is designed. Flow characteristics of the pump in inlet and outlet port is investigated through theoretical calculations and modeling simulation. The principle of fixed displacement pump dynamic compensation for the differential volumetric flow is theoretically analyzed. For the problem of big energy loss of valve control system and complex structure of the existing pump control system, the paper builds a circuit of differential cylinder controlled with PMSM driven pump and describes the implementation of dynamic compensation system. By simulation analysis of system modeling, four-quadrant operation performance and energy consumption characteristics, the feasibility of dynamic compensation system implementation is verified. At the same time these studies provide theoretical basis on further improvement of the dynamic performance of pump controlled differential cylinder and reduction of the loss.Differential cylinder system controlled with PMSM driven pump has factors of parameter variations, load disturbances, hysteresis and nonlinear that are not conducive to performance improvement. Compound control method of model following control and load torque feed-forward compensation is proposed. The motor torque and speed are observed. According to the principle of perturbation invariance, feed-forward control compensates load torque. The control strategy improves tracking performance and control property of speed system, expands frequency band, reduces the dynamic speed downhill, and improves motor disturbance rejection performance. For coupling vibration of mechanical and electrical hydraulic system, resonance ratio control is proposed. The control strategy introduces resonance ratio parameters in feedback link of load torque, doesn't change the resonant frequency of the hydraulic system, and resonance effectively is suppressed. To further improve the velocity dynamic characteristics of the differential cylinder and eliminate reciprocation velocity static error of the differential cylinder, dynamic feed-forward compensation speed close loop control is put forward. Feed-forward compensation function is designed according to open-loop characteristics of cylinder velocity and motor speed. It is real-timely called at different velocity given. The control method implements velocity symmetry of differential cylinder protruding and retracting, reduces the dynamic response time, effectively improves dynamic characteristics, enhances the velocity tracking control precision, and lower energy consumption. Finally the study builds the mathematical model and dSPACE test platform. Simulation and experimental verify the effectiveness of design.In order to eliminate static error of differential cylinder position and improve dynamic performance and robust stability of the position servo system, composite control strategy of speed, acceleration feedforward compensation and integral separation PI with anti-saturation is put forward. Speed and acceleration feed-forward function is designed according to closed-loop characteristics. Thus differential cylinder displacement achieves the desired trajectory in accordance with laws of speed and acceleration control at different given value. No load and load experiments show that the strategies increase the position tracking control accuracy, improve dynamic property, effectively suppress movement noise of the cylinder, and enhance disturbance rejection performance. The differential cylinder system controlled with PMSM driven pump is used in the clamping of injection molding machine. The system uses clamping virtual prototype as load, employs position tracking control for the mould opening and clamping. Further it verifies position servo system tracking accuracy and robustness, and lays the foundation for the engineering application.After adopted with the above-mentioned strategy, the control scheme of differential cylinder driven with PMSM and pump is used in injection molding machine system. Control characteristics and energy consumption are compared with four control schemes of asynchronous motor driven injection molding machine. Pressure and flow are adjusted by changing the motor speed in PMSM direct-drive pump controlled injection molding machine system. The system implements adaptive match control of the drive power and the executive mechanism. Simultaneously it solves the energy consumption problem when injection molding machine has been working for in part load conditions such as cooling and packing etc. PMSM driven pump system eliminates the overflow and throttling loss, and reduce energy dissipation after it replaced with asynchronous motor and valve control system. The system doesn't demand auxiliary energy sector of variable displacement mechanism and further reduces energy consumption, after fixed displacement pump substituted variable displacement pump. Under the same conditions experimental results of the five control programs show that dynamic and static performances are good, and energy consumption is significantly decreased in the injection molding machine control system.