0 Introduction

With the diversification of market demand for plastic products is more and more big, vertical injection molding machine equipment upgrading is becoming more and more quickly, the control system requirements are increasingly high, because the hydraulic vertical injection molding machine has many unique advantages in processing products, precision molding, complex shape, the system control is easy to realize, and was favored by the majority the user. But as the process of vertical injection molding machine is generally divided into locking, injection, holding pressure, melt, cooling, mold and so on several stages, in the entire production process in the processing, in order to ensure that each stage of the flow and pressure, motor load changes in large, causing the pump motor capacity is much higher than the actual, cause the waste of energy. With the development of frequency conversion technology, in recent years there have been variable frequency energy-saving injection molding machine, the control system model for the "PLC+ frequency converter, a three-phase asynchronous motor", but due to the use of three-phase asynchronous motor and the general inverter, control and response are slower, motor acceleration and deceleration time is longer (2 ~ 3S), there is no closed loop control the realization of the system flow and pressure, can not meet the rapid processing and servo control requirements, the machining accuracy can not be guaranteed. Permanent magnet synchronous motor (PMSM) using a high energy permanent magnet has the advantages of simple structure, reliable operation, small size, light weight, low inertia, fast response, high power factor, strong overload capacity, low loss, high efficiency, has been widely used in industrial robots and CNC machine tools, flexible manufacturing system, all kinds of automation equipment and other fields, has become one of the best execution elements with high accuracy, micro feed servo system; digital signal processor DSP (DigitalSignalProcessor) is largely used to improve the performance of the system, improve the system performance. In order to meet the fast hydraulic vertical injection molding machine, precision, energy-saving requirements, using TMS320F2812 as the main control chip, constitute "system mode of PC +DSP+ permanent magnet synchronous motor" flow rate and pressure of the double closed loop control, realize the servo hydraulic vertical injection molding machine of high speed, high efficiency, intelligent control.

1 control principle

For a certain type of vertical injection molding machine, because of technical parameters of cylinder piston area and the oil pump has been determined, so the output flow and motor oil pump speed is linear relationship, and the output torque and motor oil pressure within the approximate proportional. As long as the requirements according to the process of vertical injection molding machine, will be required by each procedure flow is converted into speed given signal required for each process pressure as the motor load, as long as you can with the working process of change, in time for the permanent magnet synchronous motor speed and current regulation and control, it can realize the full automatic tracking control, hydraulic vertical injection molding machine servo control purposes.

The permanent magnet synchronous motor, the speed control is now usually used by the rotor flux oriented vector control, as long as you keep is perpendicular to the d axis motor, torque equation is: Td=pm psi risq=pm psi RIS, PM as the rotor pole logarithms, psi r coupled magnetic field of the rotor on the stator flux linkage, ISD, isq for the stator current vector is in D, q axis component; based on the control of isq torque control, to realize the control of motor speed, so as to control the hydraulic vertical injection molding machine to curb the flow. The system adopts double closed loop control mode, namely the speed loop and current loop. First of all, from the host computer (PLC) according to the operation condition of vertical injection molding machine, will be required for this process flow is transmitted in a communication mode to DSP, DSP response, as given by the conversion of speed loop, and then detected by comparing the rotor speed signal, current component isqref output control torque current component of a given. Signals with the actual motor current component coordinates transform comparison, a current regulator of the PI operation, the output is obtained by inverse Park transform, Vs alpha ref, Vs beta ref, space SVPWM module according to the two signal to calculate the duty ratio of PWM, to generate PWM wave, drive inverter, frequency and amplitude adjustable three-phase sinusoidal input current of motor stator, motor drive at a speed run, control required for vertical injection molding machine of flow and pressure, so as to realize the full automatic tracking of vertical injection molding machine, reach the purpose of servo control.

The hardware circuit and the function of 2 systems

The system is mainly composed of a main circuit, DSP control circuit, detection and protection circuit to form feedback, the main circuit of rectifier, IPM inverter, motor, IPM, the Mitsubishi Co of intelligent power module PM20CSJ060, the interior has high speed and low loss IGBT a total of 6, composed of three-phase full bridge inverter circuit, and the internal integrated drive circuit, over voltage, overcurrent, overheating and under voltage fault protection circuit, when the fault signal through IPM, TMS320F2812 external interrupt PDPINT blocked DSP PWM pulse output, thereby protecting IPM from damage. Excessive pump voltage to avoid motor brake, the DC side voltage detection, the voltage detecting signal access DSP I/O port, made the software protection of voltage control, high energy brake bleeder through the discharge circuit.

The control circuit mainly by the host computer, TMS320F2812, input / output interface circuit, TMS320F2812 uses high performance static CMOS technology, frequency reaches 150MHz (6.67ns clock cycles), improve the ability of real-time control system, the internal 128K x 16 bits FLASH, 128K x 16 bit ROM, 18K x 16 bit SARAM, 1K x 16 bit a programmable memory OTP. Efficient code switching function (support C/C++ and assembler), maximum rate pipeline sampling 60ns, 12 bit AD reached 16, the PWM output channels up to 12, which makes the control system greatly reduces the price and volume reduction, improved reliability.

Motor phase current detection is a current through the Holzer sensor and resistance sampling and converted into voltage signal, then AC-DC transformation is 0 ~ voltage signal access DSP 3V A/D channel pin. Photoelectric encoder used by the system to 2500 weekly pulse, a standard interface provides 20 pin, 6 way pulse signal. Pulse by the QEP circuit 4 octave, used to calculate the rotor position and speed.

3 system software design

The software design includes the main program, subprogram of operation control etc.. The main program completed the hardware and software initialization, fault detection and processing, communication, operation, hardware initialization mainly completes the DSP settings, such as watchdog, clock, timer, ADC, SCI, I/O, event management (EV) and other settings, the software initialization of variables given an initial value of main software, DSP through the SCI communication with the host machine (PLC) to maintain communication, accept PC transfer orders, updating the variable and signs, to achieve real-time tracking control. Operation control subroutine is mainly to complete the control of permanent magnet synchronous motor in variable frequency rotor flux orientation vector, the double close loop of speed and current control.

4 Conclusion

Application of Matlab to establish the simulation model for PWSM control system, the simulation parameter settings are as follows: the permanent magnetic synchronous motor stator phase inductance of stator phase resistance: 4.8mH, 2.1, rated torque 2.2Nm, rated speed 3000r/min, rated power 690W, as given by the vertical injection molding machine film stage settings, and the speed of the motor phase current at three level membrane phase of vertical injection molding machine, 20 ~ 100ms to reach the levels required speed and current values. Show that the permanent magnet synchronous motor and high speed TMS320F2812DSP chip, in vector control at the same time the realization of motor speed and current, also realize servo for flow and pressure machine work of vertical injection control system with dynamic and static response performance can be good, improve the control speed and precision of the system, and make the the system has the advantages of simple hardware, high overload capacity and price advantages.