Selection and design of various functional components of the control system:
1. Single-chip microcomputer selects 8031 ​​single-chip microcomputer produced by INTEL company
Single chip microcomputer
It mainly takes the signal processing of the control system through the parallel 8255 port: the receiving system sets the signal for torque, valve opening, closing and valve opening, and provides the control signal required by the three-phase PWM wave generator; Fault signal and alarm signal; processing the detection signal of current, voltage, position and the like received through the analog input port; providing a working state signal for displaying the electric actuator; executing a control signal from the control system, and feeding back the signal to the control system;
2. Three-phase PWM wave generator PWM wave generation usually has two methods of analog and digital. The analog circuit is complex, with temperature drift, low precision, and limits the performance of the system. The digital method calculates the switching points by computer according to different digital models, and stores them in the memory, and then generates PWM waves by looking up the table and necessary calculations. This method occupies a large amount of memory and cannot guarantee the accuracy of the system. In order to meet the PWM wave control signal required by the intelligent power module, the microprocessor has enough time to perform the functions of detection, protection and control of the whole system. The SA8282 produced by MITEL is used as the three-phase PWM generator. The SA8282 is a dedicated large-scale integrated circuit with an independent standard microprocessor interface. The chip contains control information such as waveform, frequency, and amplitude.
3. Intelligent Inverter Module IPM In order to meet the requirements of small size and high reliability of the actuator, the motor power supply adopts the intelligent power module IPM. The actuator is mainly suitable for three-phase asynchronous motors with a power of less than 5.5 kW, with a rated voltage of 380 V and a power factor of 0.75. According to the calculation, the intelligent power module PM50RSA120 made in Japan can meet the system requirements. The power module integrates a power switch, a driving circuit and a braking circuit, and has built-in overcurrent, short circuit, undervoltage and overheat protection and alarm output, and is a high performance power switching device.
4. Position detection circuit position detection circuit is an important part of the actuator, its function is to provide accurate
Mechatronics position signal. The key issue is the selection of position sensors. In the conventional electric actuator, a winding potentiometer, a differential transformer, a conductive plastic potentiometer, and the like are often used. The short life of the wirewound potentiometer was eliminated. The differential transformer is limited due to the short linear region and unsatisfactory temperature characteristics. Conductive plastic potentiometers are currently popular, but they have contacts, and the lifespan is not likely to be long and the accuracy is not high. The position sensor used by the author is a pulse digital sensor. This sensor is non-contact and has the characteristics of high precision, wireless zone limitation, high stability and no temperature limitation. 5. Voltage, current and detection The detection voltage and current are mainly used to calculate the torque of the motor, as well as the short circuit of the inverter output circuit, phase failure protection and fault diagnosis of the inverter module. Since the frequency range of the current and voltage output by the inverter is 0 to 50 Hz, the conventional current and voltage transformers cannot meet the requirements. In order to quickly reflect the current, the Hall-type current transformer is used to detect the three-phase current of the IPM output, and the voltage-dividing circuit is used for the detection of the IPM output voltage.
6), communication interface In order to realize computer networking and remote control, MAX232 is selected as the serial communication interface of the system. There are two identical level conversion circuits inside MAX232, which can convert the TTL level of 8031 ​​serial port output into RS. The -232 standard level converts the RS-232 standard level sent by other microcomputers into a TTL level to 8031 ​​to realize communication between the MCU and other microcomputers.
7. Clock circuit clock circuit is mainly used to provide sampling and control
The time required to calculate the cycle, speed, and calendar. The clock circuit DS128 is selected in the paper.
Mechatronics 87. The DS12887 has 114 bytes of user non-volatile RAM inside, which can be used to store data that needs to be stored for a long time.
8. Liquid crystal display unit In order to realize the man-machine dialogue function, the MGLS12832 liquid crystal display module is used to form the display circuit. Adopt configuration display mode. Through the menu selection, the valves, torque, limit, motor, communication and parameters can be set or debugged separately. And the combination of text and graphics, the display is intuitive and clear.
9. Program self-recovery circuit In order to ensure that the system can automatically return to normal when the program is out of strong interference, the MAX705 is used to form a self-recovery circuit, and the monitoring program runs. As shown in Figure 2-3, the circuit consists of the MAX705, NAND gate, and differential circuitry. The working principle is: once the program is out of the box, the WDO changes from high to low. Due to the function of the differential circuit, the NAND gate input pin 2 goes high, and the change of the pin 2 level makes the NAND. The gate outputs a positive pulse, which causes the MCU to generate a reset. After the reset is completed, the program sends a positive pulse to the WIG pin of the MAX705 through the P1.0 port, so that the WDO pin returns to the high level, and the program continues from the recovery circuit. The monitor runs.
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