Abstract: This paper addresses the complex process characteristics of a six-sided diamond press and designs and develops a computer-automatic control system for it. The system mainly consists of two parts: hardware structure design and software design. The software part primarily solves the positioning control and synchronization adjustment problems of the press, and presents the process curve setting method, control algorithm, and main operating results. This control device, combined with a six-sided diamond press and related hydraulic system of a superhard materials company, forms a fully automated diamond production device. It features a full-view interface, touchscreen operation, novel control algorithm, excellent graphical interface, high control precision, and ensures the quality of the synthesized diamond. Keywords: synthetic diamond; cubic synthetic diamond press; monitoring system Abstract: This paper develops an automatic control system for a cubic synthetic diamond press, focusing on the complex craftwork characteristics. The system mainly includes hardware and software designs. Problems related to orientation control and synchronous tuning of the press are successfully solved. The initialization of the craftwork curve, control arithmetic, and running results are also introduced. The control equipment, combined with a hydraulic pressure system for the cubic synthetic diamond press, forms the complete automatic control production equipment. This system features a full inspection window interface, operation via a touch screen, novel control arithmetic, and improved graphical interfaces to ensure the quality of synthetic diamonds . Key words: synthetic diamond; cubic synthetic diamond press; inspection system 1. Introduction Diamond, also known as carbon, is an allotrope of carbon and one of the earliest and hardest naturally occurring minerals discovered by humankind. Graphite can be synthesized by altering its atomic structure under high temperature and pressure conditions and the catalytic action of a catalyst. The unique properties of synthetic diamond superhard materials have led to their widespread application in building materials and construction industries, geological drilling, oil extraction, machining, and optical instruments. The six-sided diamond synthesis press is a key piece of equipment in my country's superhard material production. However, due to the relatively backward production technology of synthetic diamonds in China, the existing production equipment has a low degree of automation, with a significant portion still operating manually. In particular, the current pressure and heating control is insufficient to meet the requirements of diamond production processes, resulting in low precision and producing mostly low- to medium-grade diamonds. To address this, the author designed and developed a novel automatic control system for the six-sided diamond press. This system, integrated with a six-sided diamond press and related hydraulic systems of a superhard materials company, forms a diamond production unit. This monitoring system features a full-view interface and touchscreen operation, a user-friendly graphical interface, and high control precision, ensuring the quality of the synthesized diamonds. 2. Production Process of a Six-Sided Diamond Press: The six hydraulic cylinders of the synthetic diamond press—upper, front, right, lower, rear, and left—move from six directions toward the graphite pyrophyllite composite block located at the center of the press, thus forming a six-sided press. The hydraulic oil output from the hydraulic pump controls the forward and backward movement of each hydraulic cylinder's hammers through the opening and closing of valves in the oil circuit. The ultra-high pressure required for synthetic diamond synthesis is achieved through a booster. The common production process for synthetic diamonds is as follows: The graphite pyrophyllite block to be synthesized is placed in the center of the press. The "Idle Forward" button is pressed, and the top, front, and right cylinders advance to their stop positions, working together with the bottom, rear, and left cylinders to gently press the graphite pyrophyllite block from six sides. The "Pressure Synthesis" button is pressed, entering the "Liquid Filling" step. Simultaneously, the six cylinders advance towards the center of the press, compressing the graphite pyrophyllite block. Then, the "Overpressure Connection" step applies high temperature and ultra-high pressure to the graphite pyrophyllite block, ensuring the heating power and pressure follow a pre-set process curve. After the heating and pressure holding time is reached, the system automatically switches to the "Pressure Relief" and "Return" steps, returning the six cylinders to their starting positions, completing one work cycle. 3. Hardware Structure Design of the Automatic Control System for the Diamond Press This system consists of a control cabinet, a handheld device, and field instruments (components). The control cabinet includes an industrial control computer, a touch screen display, process input/output modules, valve proportional amplifiers, a DC power supply, thyristors and power control boards, power transmitters, and related electrical control components. The field components include displacement sensors, pressure transmitters, temperature sensors, current transformers, and electro-hydraulic proportional valves. The control system I/O channels are shown in Figure 1. This system receives six cylinder displacement, oil pressure, voltage, current, oil temperature, and water temperature signals through 24 A/D converters, various switch input signals through 64 input points, various electro-hydraulic proportional control signals and heating power control signals through 12 D/A converters, and various switch output signals through 32 output points. [align=center] Figure 1 I/O Channels[/align] 4. Automatic Control System Software Design for the Diamond Press The automatic control system software for the six-sided diamond press is developed using a combination of industrial control configuration software and a visual programming language. The process setting curves are written in a visual programming language, the help file is in HTML format and can be viewed using an IE browser; all other configurations are done using industrial control configuration software. Two-way dynamic data exchange between industrial control configuration software and visual programming programs is achieved through DDE (Dynamic Data Exchange). The main screen of the press process flow and monitoring system, as well as other related screens, can be freely switched via the touchscreen by clicking corresponding buttons. This enables dynamic graphical display of the process flow, real-time data bar chart display, real-time data trend curve display, parameter over-limit alarms, and rapid setting of pressure and power process curves; historical data recording and recall; and online tuning of various control system parameters under authorized password conditions. 4.1 System Features and Control Functions: ¨ Employs electro-hydraulic proportional control technology to achieve continuous control of hydraulic system pressure, ultra-high pressure, and six-cylinder displacement. ¨ Utilizes industrial control computer control technology to achieve a full-view interface and touchscreen operation; advanced technology, convenient operation, and reliable control. * High-precision displacement sensors and cantilever displacement detection mechanisms are used to measure the displacement of the six cylinders, significantly improving positioning control accuracy. A novel control algorithm is proposed, utilizing the unidirectional capacity characteristics of the cylinders in the six-sided diamond press system to precisely achieve six-cylinder positioning control with no overshoot and no residual error. A new press filling synchronous adjustment control scheme is adopted, allowing each cylinder to be adjusted independently with minimal mutual influence and convenient adjustment. * A pressure and power process curve program setting module has been successfully developed, allowing users to freely set up to 15 segments of programmed pressure and power increase curves. Setting, modifying, and saving are very convenient and intuitive, and a large number of pre-stored process setting curves can be used. Bidirectional dynamic data exchange between the industrial control configuration software and the process curve program setting module is achieved through DDE, enabling synchronous real-time display. * During the overpressure stage, the program setting curve is accurately tracked, resulting in good control, stable pressure holding, and minimal fluctuations, which is beneficial for diamond synthesis. An automatic compensation control method is used to achieve power control, effectively overcoming the impact of grid voltage fluctuations on synthesis. 4.2 Positioning Control and Synchronization Adjustment Design of the Press The traditional six-cylinder positioning control method for a six-sided diamond press basically adopts a positional control method. During the "idle stroke forward" step, an inductive proximity switch detects whether the three cylinders have reached the stop position. Once reached, the hydraulic oil supply to the cylinders is cut off. However, during the "filling" step, the positioning of the six cylinders is no longer controlled. The shortcomings of this method are: ① Inaccurate stop of the hammer during the "idle stroke forward" step, easily resulting in failure to press the pyrophyllite composite block or crushing the pyrophyllite composite block; ② Difficulty in adjusting the stop position; ③ Due to the inability to control the filling level, the filling strokes of the six hammers are easily out of sync, easily causing hammer squeezing, hammer collision, and explosion accidents. To address the defects of the above method, this system proposes a six-cylinder positioning control method for a six-sided diamond press with no overshoot and no residual error. Six electro-hydraulic proportional valves are used to control the oil supply to the six cylinders respectively, thereby controlling the forward speed and stop position of each cylinder. Different control methods are used for the positioning control of the three active cylinders and the three dead cylinders. The cylinder positioning control block diagram is shown in Figure 2. The upper part of the block diagram outputs the proportional valve opening control quantities for the three cylinders' "idle stroke forward" step using a specific "idle stroke forward algorithm," while the lower part outputs the proportional valve opening control quantities for the three cylinders' "filling" step using a specific "filling algorithm." By tuning the corresponding control parameters, all three cylinders can be stopped at a stroke of 0mm during the "idle stroke forward" step, and all six cylinders can be stopped at the filling position setting during the "filling" step. Based on the current actual step, the selector selects the corresponding proportional valve opening control quantity, which is then converted into an analog quantity by a limiter and a D/A converter before being sent to the valve proportional amplifier and electro-hydraulic proportional directional valve to control the "idle stroke forward" or "filling" stroke of the three cylinders, respectively. For the three stationary cylinders, since there is no "idle stroke forward" step, the control method is slightly simpler than that for the three cylinders. [align=center]Figure 2 Positioning control of the cylinder[/align] 4.3 Process Curve Setting Screen Since there is no suitable tool for freely setting process curves in the industrial control configuration software platform, this system uses a visual programming language to generate the process curve setting module. The process curve setting screen is shown in Figure 3. A process curve setting screen has 10 tabs for selection. Users can freely set a set of program pressure boosting and power boosting curves on each tab. Each curve can consist of up to 15 segments. The right side of the screen has buttons for setting the coordinates of the inflection points of each segment of the curve, namely the time-pressure group and the time-power group. The values ​​of the inflection point coordinates can be changed by inputting the numeric keypad or clicking the increase/decrease buttons with the mouse. Simultaneously, the setting curve graph on the screen will be automatically generated and changed synchronously in a WYSIWYG manner. After setting or selecting, pressing the "Apply" button will officially select this set of setting curves for the currently running program setting curves. [align=center]Figure 3 Process Curve Setting Screen[/align] When the press is connected to overpressure, the data of the selected program setting curve is transmitted to the industrial control configuration software through DDE dynamic data exchange, as the set value of the pressure and power automatic control system. 4.4 Main Parameter Display and Adjustment Screen The main parameter display and adjustment screen of the system is shown in Figure 4. The upper left of the screen displays the synthesis time; the right side is the trend recording curve; the middle of the screen has the press parameter adjustment buttons, which can adjust the start position of the three cylinders, the idle stroke forward stop hammer position, the liquid filling stop hammer position and the synthesis position respectively; the upper left of the screen displays the displacement bar graph of the six cylinders, and the step display is below the displacement bar graph; the lower left shows the set value, fine adjustment value and real-time value of the process parameters; the bottom row of the screen displays the operating status of each pump and solenoid valve. [align=center]Figure 4 Parameter Display and Adjustment Screen[/align] 5. Conclusion The author's innovations are: 1. Employing electro-hydraulic proportional control technology to achieve continuous control of hydraulic system pressure, ultra-high pressure, and six-cylinder displacement; 2. Proposing a novel control algorithm that utilizes the unidirectional capacity characteristics of the cylinders in a six-sided diamond press system to accurately achieve six-cylinder positioning control and synchronous filling control without overshoot or residual error; 3. Using a visual programming language to generate a process curve setting module, each curve can consist of up to 15 segments, and the set curve graph is WYSIWYG. Field tests and long-term user use have shown that this system has a good human-machine interface, rich data display and graphical screens, convenient operation and monitoring, high cylinder positioning control accuracy, and can accurately track the pressure and power program setting curves during the overpressure stage, ensuring the grade of the synthetic diamond and significantly reducing hammer wear. According to calculations by a superhard metal materials company in Henan, after using this control system, the service life of the press top hammer is extended from more than 3,000 pieces/hammer/set of general pressed synthetic blocks to more than 9,000 pieces/hammer/set. Each press can save 5 to 6 sets of top hammers per year, saving about 40,000 yuan in costs. A medium-sized synthetic diamond production enterprise with 100 presses can save 4 million yuan per year. References [1] Wang Ling, Zhao Mingguang. Design of computer control system for fiber winding machine [J]. Microcomputer Information, 2006, 11S: 126-127, 108 [2] Mo Jinhai, Li Haibiao. Design instrument for intelligent pressure measurement and control system of artificial diamond press [J]. Journal of Instrumentation, 2006, 27 (6): 493-495 [3] Jiang Ronghua, Zheng Limin. Research on intelligent heating power supply of six-sided diamond press [J]. 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