The intelligent control of the artificial diamond synthesis process is primarily achieved through the implementation of advanced computer control technology and intelligent control strategies to enable comprehensive and precise monitoring and control of key process parameters.
1. Overall Intelligent Control System Architecture
The computer control system for the artificial diamond press (such as the Y-500 cubic press) mainly replaces the machine's original electrical control system. The press itself is composed of the electrical control system and the hydraulic system.
Intelligent Functionality and Goals:
Comprehensive Control: The system utilizes computer control technology to perform all-around control and monitoring of the entire artificial diamond production process, significantly improving the working reliability and production efficiency of the press machine.
Core Functions: It possesses intelligent functions including logic analysis, mathematical calculation, optimal dynamic control, state detection, analysis and processing of abnormal situations, automatic process tracking, dynamic display, a user-friendly human-machine interface, and network communication.
Software Technology: The field control computer software applies intelligent PID control theory, fuzzy PID control theory, and PID parameter self-tuning technology.
Prediction and Advance Control: The fault analysis and processing module software includes a state prediction function. This allows the prediction of the development trends for the ram displacement, system pressure, and system heating power. Based on this analysis, the computer performs advance control over all executive systems to ensure stable and safe operation of the equipment.
Components: The control system consists of pressurization control, heating control, ram displacement control, comprehensive analysis and processing, field monitoring, and central monitoring.
2. Intelligent Control Strategies for Key Process Parameters
The synthesis outcome (yield and quality) of artificial diamond is largely determined by the appropriate matching of temperature and pressure. Intelligent control focuses on precise regulation of these variables.
A. Pressurization Control (Pressure) – Using Fuzzy PID Control
Pressurization control demands high precision and speed. The process requires multiple stages (2 to 6 segments) for supercharging and pressure holding. The pressure needs to be increased from approximately 10 MPa to around 90 MPa in segments over several minutes, and the overshoot cannot exceed 0.3 MPa.
Control Strategy: A fuzzy-PID composite control method is utilized to enhance the accuracy of fuzzy control. The pressure control strategy employs a multi-modal segmented control algorithm which synthesizes the advantages of Proportional (P), Fuzzy, and Proportional-Integral (PI) control.
Control Breakdown: Supercharging uses the main pump switch control, while pressure holding utilizes the auxiliary pump compensation with fuzzy PID control.
Switching Mechanism:
When the deviation exceeds a specific threshold, Proportional control is engaged for rapid tracking adjustment.
When the deviation falls below the threshold, it switches to Fuzzy control to improve system damping characteristics and reduce overshoot.
When the error (linguistic variable) is zero, it switches to PI control (the integrator is shut down when the absolute error is zero or saturation occurs).
Robustness: Compared to traditional PID controllers, the Fuzzy PID controller enhances the system's robustness against external interference and internal parameter changes, reducing overshoot and improving dynamic characteristics.
B. Heating Control (Power/Temperature) – Using Expert-based Intelligent Self-tuning PID Control
The heating control process typically starts after the supercharging reaches 30 MPa, and involves multiple stages of heating and holding. Heating power control needs to be precise, but temperature exhibits a lagging nature due to the characteristics of the heat transfer medium (pyrophyllite, woven ribbon, alloy rams).
Control Strategy: The heating power control adopts an expert-based intelligent self-tuning PID control algorithm based on pattern recognition.
Intelligent Self-tuning Mechanism:
When the output deviates from the setpoint or when the system is disturbed, pattern recognition is performed on the time characteristics of the system error (e).
This identifies characteristic parameters of the response curve, such as overshoot, damping ratio, decay oscillation period, and rise time.
The deviations between these measured characteristic parameters and their preset values are input into the expert system.
These corrections are applied to the conventional PID controller, modifying its parameters to ensure the heating power response curve characteristics meet the technical requirements.
Performance: Practical implementation confirms that this intelligent self-tuning PID algorithm ensures stable operation and satisfies the steady-state control accuracy and dynamic response indices for heating power.
C. Ram Displacement Control
The synchronization accuracy of the six rams during the liquid filling process is a critical index for diamond synthesis. It is required that the synchronization difference be less than 0.01 mm. Given the extremely short filling time (only 4 to 5 seconds), the system must accurately sample and process 20x6 sets of displacement data.
Control Strategy: To ensure control accuracy, the system employs high-speed processing instructions, floating-point arithmetic instructions, and various anti-interference measures.
3. Monitoring and Human-Machine Interaction
Field Monitoring: Field monitoring uses a touch-screen graphic display operating terminal. This terminal is easy to operate, displays clearly, and is reliable. It dynamically displays the operating conditions, including switching quantities, analog quantities, process operation curves, and fault alarm types. It also allows for setting parameters such as working parameters, displacement parameters, PID parameters, and temperature/pressure curves.
Central Monitoring: Real-time and historical data from all press machines are transmitted via the field bus to the central monitoring computer. This enables production management and technical analysis, allowing staff to view and print the operating status and historical data of specific presses. The central monitoring system software is built using Kingview 6.5.