Abstract: This paper proposes a novel electric actuator design scheme, detailing the selection and design of its functional components, valve position and speed control principles, and solutions to various key problems. This actuator integrates the valve, servo motor, and controller, employing an 8031 ​​microcontroller and frequency conversion technology to achieve valve speed and position control. It solves technical problems such as precise valve positioning, flexible valve switching, limit position judgment, motor protection, and analog signal isolation. Field operation results show that this electric actuator has advantages such as fast action, comprehensive protection, and easy communication with computers. Keywords: Mechatronics, Intelligent High-Flow, Electric Actuator 1 Introduction In modern production process control, actuators play a crucial role, serving as an indispensable component of automatic control systems. Existing domestically produced high-flow electric actuators suffer from outdated control methods, numerous mechanical transmission mechanisms, complex structures, low positioning accuracy, and poor reliability. Furthermore, the actuator's overall operating speed depends on the output shaft speed of its motor and the reduction ratio of its internal reduction gears; once manufactured, this speed is fixed and cannot be adjusted, resulting in limited versatility. The entire mechanism lacks comprehensive protection and fault diagnosis measures, as well as necessary communication methods, resulting in poor system security and inconvenience for computer networking. For these reasons, the control system of the traditional high-flow electric actuator suffers from poor reliability and stability. With the application of computer networks, fieldbus, and other technologies in industrial processes, this type of actuator is far from meeting the requirements of industrial production. The high-flow electric actuator designed by the author adopts mechatronics technology, integrating the valve, servo motor, and controller into one unit, using an asynchronous motor to directly drive the opening and closing of the valve. Through a built-in frequency converter and a fuzzy neural network, it achieves control over valve action speed, precise positioning, flexible switching, and motor torque. This electric actuator eliminates the need for contactors and thyristor commutator modules for controlling the forward and reverse rotation of the motor, mechanical transmission devices, and complex and expensive control cabinets and distribution cabinets, offering advantages such as fast action, comprehensive protection, and ease of computer networking. Actual operation shows that the actuator operates stably and reliably. 2 Hardware Design and Working Principle of the Electric Actuator The block diagram of the electric actuator control system is shown in Figure 2-1. The intelligent actuator is mainly divided into a control part and an execution drive part. The control section mainly consists of a microcontroller, a PWM wave generator, an IPM inverter, A/D and D/A conversion modules, a rectifier module, input/output channels, fault detection, and alarm circuits. The execution drive section mainly includes a three-phase servo motor and position sensors. System working principle: Hall current and voltage sensors and position sensors detect the three-phase output current and voltage of the inverter module and the valve position signals, which are then sent to the microcontroller after A/D conversion. The microcontroller controls the PWM wave generator through an 8255, and the generated PWM wave acts on the IPM inverter module via optocoupler to realize the variable frequency speed regulation of the motor and valve position control. The DC voltage signal required for the inverter module to work is obtained by full-bridge rectification of the 380V power supply by the rectifier circuit. Selection and Design of Functional Components in the Control System: 1) The microcontroller selected is the Intel 8031 ​​microcontroller, which mainly handles signal processing for the control system through the parallel 8255 port: receiving system setting signals for torque, valve opening, closing, and valve opening degree, and providing the control signals required by the three-phase PWM wave generator; processing fault and alarm signals from the IPM; processing current, voltage, and position detection signals received through the analog input port; providing and displaying the working status signals of the electric actuator; executing control signals from the control system and providing feedback signals to the control system; 2) The three-phase PWM wave generator typically uses two methods for generating PWM waves: analog and digital. The analog method has complex circuitry, temperature drift, and low accuracy, limiting system performance. The digital method calculates the switching points using a computer according to different digital models, stores them in memory, and then generates the PWM wave through table lookup and necessary calculations. This method requires more memory and cannot guarantee system accuracy. To meet the PWM control signal requirements of the intelligent power module and ensure sufficient time for the microprocessor to perform system detection, protection, and control functions, the SA8282 from MITEL is selected as the three-phase PWM generator. The SA8282 is a dedicated large-scale integrated circuit with an independent standard microprocessor interface; the chip internally contains control information such as waveform, frequency, and amplitude. 3) Intelligent Inverter Module (IPM): To meet the requirements of small size and high reliability of the actuator, the motor power supply uses an intelligent power module (IPM). This actuator is mainly suitable for three-phase asynchronous motors with a power rating of less than 5.5kW, a rated voltage of 380V, and a power factor of 0.75. Calculations show that the Japanese-made intelligent power module PM50RSA120 can meet the system requirements. This power module integrates power switching, drive circuit, and braking circuit, and has built-in overcurrent, short circuit, undervoltage, and overheat protection, as well as alarm output; it is a high-performance power switching device. 4) Position Detection Circuit: The position detection circuit is an important component of the actuator, and its function is to provide accurate position signals. The key issue is the selection of the position sensor. Traditional electric actuators often use wound potentiometers, differential transformers, and conductive plastic potentiometers. Wound potentiometers are obsolete due to their short lifespan. Differential transformers are limited by their short linear range and unsatisfactory temperature characteristics. Conductive plastic potentiometers are currently popular, but they have contacts, resulting in a limited lifespan and low accuracy. The position sensor used in this paper is a pulse digital sensor, which is contactless and features high accuracy, no linear range limitations, high stability, and no temperature limitations. 5) Voltage and Current Detection: Detecting voltage and current is mainly for calculating motor torque, as well as for short-circuit and phase-loss protection of the inverter output circuit and inverter module fault diagnosis. Since the frequency range of the inverter output current and voltage is 0–50Hz, conventional current and voltage transformers cannot meet the requirements. To quickly reflect the current magnitude, a Hall-effect current transformer is used to detect the three-phase current output of the IPM, and a voltage divider circuit is used for detecting the IPM output voltage, as shown in Figure 2-2. 6) Communication Interface: To achieve computer networking and remote control, the MAX232 is selected as the system's serial communication interface. The MAX232 has two identical level conversion circuits internally, which can convert the TTL level output from the 8031 ​​serial port to the RS-232 standard level, and convert the RS-232 standard level from other microcomputers to TTL level for the 8031, enabling communication between the microcontroller and other microcomputers. 7) Clock Circuit: The clock circuit is mainly used to provide the sampling and control cycle, the time required for speed calculation, and the calendar. The DS12887 clock circuit is selected in this paper. The DS12887 has 114 bytes of user non-volatile RAM, which can be used to store data that needs to be stored for a long time. 8) LCD Display Unit: To achieve human-machine interaction, the MGLS12832 LCD display module is selected to form the display circuit. A configuration display method is adopted. Through menu selection, signals such as valves, torque, limit switches, motors, communication, and parameters can be set or adjusted. A combination of text and graphics is used for intuitive and clear display. 9) Program Error Self-Recovery Circuit: To ensure the system can automatically recover to normal when the program goes out of bounds under strong interference, a MAX705 is selected to form a program error self-recovery circuit to monitor program operation. As shown in Figure 2-3, this circuit consists of a MAX705, a NAND gate, and a differentiating circuit. The working principle is as follows: Once the program goes out of bounds, WDO changes from high to low. Due to the action of the differentiating circuit, the input pin 2 of the NAND gate becomes high. This change in the level of pin 2 causes the NAND gate to output a positive pulse, causing the microcontroller to generate a reset. After the reset, the program sends a positive pulse to the WDI pin of the MAX705 through port P1.0, causing the WDO pin to return to high level, and the program error self-recovery circuit continues to monitor program operation. Mechatronics Intelligent High-Flow Electric Actuator 3. Valve Position and Speed ​​Control Principle The block diagram of the valve position and speed control principle is shown in Figure 3-1. A dual-loop control scheme is adopted, where the inner loop is the speed loop and the outer loop is the position loop. The speed loop primarily compares the current speed with the set speed sent by the speed setpoint generator. It adjusts the motor speed by changing the carrier frequency of the PWM wave generator through the speed regulator. The speed regulator employs a fuzzy neural network control algorithm (details will be described separately). The outer loop provides the set speed value to the inner loop based on the current position speed setting via the speed setpoint generator. Because the high-flow-rate valve actuator operates through acceleration, constant speed, and deceleration phases, the duration of each phase, the magnitude of the acceleration, and the starting point of constant speed or deceleration are all related to the setpoint position, the current position, and the operating speed. The speed setpoint generator works by comparing the actual valve position with the setpoint valve position. When they are not equal, it accelerates with a constant acceleration. The deceleration point is calculated based on the current speed, valve position value, and the setpoint valve position value. Figure 3-2 shows a typical operating speed diagram of the actuator, composed of several segments of broken lines with different rates of change. The point on the curve where the speed begins to change is called the starting point of the segment, and the corresponding time is called the segment start time, as shown in Figure 3-2 as t(i) (i = 0, 1, 2, ...). The corresponding speed is called the segment start speed, as shown in Figure 3-2 as v(i) (i = 0, 1, 2, ...). Let the rate of change of the speed in the i-th segment be ki, then we have: Where: Δv is the speed change value between two segment points, Δv = vi + 1 - vi; Δt is the time between two segments, Δt = ti + 1 - ti. Obviously, when ki = 0, it is a constant speed segment; when ki > 0, it is an acceleration segment; and when ki < 0, it is a deceleration segment. The speed setpoint at any time is: Ts is the sampling period. The value of the rate of change ki is determined by the given position, the current position, and the magnitude of the running speed. 4. Solution of Key Technical Problems This electric actuator adopts the latest variable frequency speed control technology, and the motor drive power is less than 5.5kW. Users can set the torque characteristics as needed and set the speed according to the controlled valve. The speed is divided into three modes: multi-turn, linear stroke, and angular stroke. The control system is a closed-loop system consisting of valve position setpoint and valve position feedback signals. Its control characteristics depend on the operating mode and speed, and it features automatic overcurrent protection, overload protection, overpressure protection, underpressure protection, overheating protection, phase loss protection, and stall protection. The key technical problems solved by this actuator are: 1) Flexible valve switching: Flexible switching is mainly to ensure that the valve does not jam or get damaged when it is closed or fully open. The microprocessor inside the actuator calculates the output torque based on the measured inverter output voltage and current. Once the output torque reaches or exceeds the set torque, the speed is automatically reduced to avoid excessive impact inside the valve, thus achieving optimal closure and over-torque protection. 2) Valve position limit determination: The valve position limit refers to the fully open and fully closed positions. In traditional actuators, this position is detected by mechanical limit switches. Mechanical limit switches have low accuracy, are prone to loosening during operation, and have poor reliability. In this paper, the limit position of the electric actuator is obtained by detecting the increment of the position signal. The principle is that the microcontroller compares the current position signal with the previous signal. If there is no change or the change is small, it is considered that the limit position has been reached, and the power supply to the asynchronous motor is immediately cut off to ensure the safe closure or full opening of the valve. This eliminates the need for mechanical limit switches and complex adjustments during debugging. 3) Motor protection: To prevent the motor from burning out due to overheating, the microcontroller continuously monitors the actual operating temperature of the motor through a temperature sensor. If the temperature sensor detects that the motor temperature is too high, it automatically cuts off the power supply. The temperature sensor is built into the motor. 4) Accurate positioning: Traditional electric actuators quickly reach their rated operating speed after the asynchronous motor is powered on. When approaching the stop position, after the motor is powered off, due to mechanical inertia, the valve cannot stop immediately, resulting in varying degrees of overtravel. This overtravel is usually corrected by controlling the motor to rotate in reverse. The mechatronic high-flow electric actuator determines the position of the deceleration point and the rate of change of the deceleration segment ki in advance based on the difference between the current position and the given position, as well as the magnitude of the operating speed. This allows the valve to achieve precise fine-tuning and positioning at a lower speed, thereby minimizing overtravel. 5) Analog Signal Isolation. The DC voltage and the three-phase output voltage of the frequency converter have inconsistent addresses, resulting in a high common-mode voltage. To ensure system safety, they must be isolated from each other. An isolated linear amplifier circuit is constructed using LM358 and 4N25. As shown in Figure 4-1, two independent positive and negative power supplies, ±15V and ±12V, are used. If the inverting input potential of operational amplifier A deviates positively from virtual ground due to disturbance, the output potential of operational amplifier A will decrease, thus increasing the luminous intensity of the optocoupler, reducing its collector-emitter voltage, and finally lowering the inverting input potential of operational amplifier A, returning it to normal. If the inverting input potential of A deviates negatively from virtual ground, it can also return to normal. This enhances the system's anti-interference capability. 5 Conclusion This actuator integrates microcomputer technology and actuator technology, and is a new type of terminal control unit. Its motor is controlled by an internally integrated frequency converter. Therefore, the same intelligent actuator can have different operating speeds and shut-off torques within a certain range. This intelligent actuator employs LCD technology. Utilizing a built-in LCD panel, it can display not only the valve's open/closed status and normal operating opening degree, but also allow for menu-based parameter settings. Furthermore, it displays fault information when a system malfunctions. In summary, this actuator integrates measurement, decision-making, and execution functions, aligning with the development trend of electric actuators. Its successful development provides new insights into the research and development of electric actuators.