Servo control technology, by constructing a closed-loop servo control system, enables precise control of the ultra-high pressure relief process in cubic presses, overcoming issues such as discontinuous pressure relief and poor linearity found in traditional control methods (e.g., solenoid valve on-off control, stepping motor control). This addresses the higher demands for equipment performance and synthesis stability in high-performance super-hard material synthesis.
Core Control Principle: Dynamic and precise control of the gap between the conical valve core and the valve seat.
The ultra-high pressure relief valve of a cubic press primarily consists of a servo motor, relief valve body, conical valve core, conical valve seat, ultra-high pressure oil inlet, and low-pressure oil outlet. The most critical components are the conical valve core and the valve seat.
The fundamental way to control the pressure relief speed is by controlling the size of the gap between the conical valve core and the valve seat: a larger gap results in faster pressure relief, and vice versa.
However, in practical applications, the relationship between pressure relief speed and the gap is not a fixed linear one. As pressure decreases, a larger gap is required to maintain the pressure relief speed. Therefore, dynamically and precisely controlling this gap is the key technology.
Servo control technology innovatively uses a servo motor to replace the stepping motor to drive the ultra-high pressure relief valve mechanism.
A servo motor is a high-precision executive component. When configured with servo control technology, it can convert voltage signals into angular displacement or angular velocity output on the motor shaft, thereby precisely adjusting torque or speed to achieve accurate control of speed and position parameters.
Advantages of servo motors compared to stepping motors include:
Constant torque output, where the output torque is largely unaffected by the pressure relief speed, solving the problem of stepping motors where output torque is inversely proportional to speed, often leading to valve core jamming.
Much better high-speed response performance than stepping motors.
Closed-loop control with high precision, ensuring accurate valve reset. This avoids the disadvantage of stepping motors' open-loop control, which is prone to losing steps.
The servo controller drives the servo motor to rotate, dynamically and precisely adjusting the opening gap between the conical valve core and the valve seat, meeting the requirements for smooth and linear ultra-high pressure relief.
Its adjustable torque characteristic allows setting different torque values for closing and opening the relief valve, ensuring safe closing and timely opening.
Its fast response capability can quickly reset the valve core in case of abnormal pressure relief, preventing accidents caused by sudden pressure drops.
Construction of a Closed-Loop Servo Control System.
The system consists of a Programmable Logic Controller (PLC), a servo control system (including a servo motor and servo drive), and a high-precision pressure sensor.
An OMRON CP1H series PLC (CP1H-XA40DT-D) and a Siemens V90 servo control system (servo motor 1FL6042-1AC61-0AB1, servo drive 6SL3210-5FE10-4UA0) are used.
Hardware Design: The PLC acts as the lower machine, collecting data from the pressure sensor and uploading it in real-time to the human-machine interface (HMI), which consists of an industrial computer and a display. The HMI converts pressure data into production pressure curves to monitor the pressure relief process in real-time. The servo controller is selected for position control mode, providing precise pulses. Communication between the HMI and the PLC uses the RS485 communication protocol.
Software Design: An intelligent PID control algorithm is introduced. This algorithm library combines theoretical design with experimental data to establish a safe pressure relief algorithm that relates pressure relief speed to control parameters.
Control Implementation Process.
During the pressure relief phase, the PID control software automatically matches empirical pressure relief control parameters from the algorithm library based on the process-set pressure relief speed (SV(t)), ensuring safe initiation of the pressure relief process.
The PID control software continuously calculates the measured pressure relief speed (PV(t)) and compares it with SV(t).
If a deviation exists, the PID control software automatically adjusts the pressure relief control parameters based on the trend and deviation of PV(t), and outputs control pulses to the servo controller, driving the servo motor to open the pressure relief valve mechanism. It also records the pulse amount, thereby achieving closed-loop control and linear pressure relief.
For different super-hard material synthesis processes (e.g., significant differences in pressure control, frequent changes in pressure relief speed, uncertainty in pressure relief parameters), the intelligent pressure control software can solve these problems without manual intervention.
Full-process segmented pressure relief and inflection point handling: When synthesizing similar super-hard materials, the pressure relief speed varies across different pressure segments, typically divided into 2-3 segments of slow, medium, or fast pressure relief curves. The software includes an inflection point judgment program. When an inflection point is encountered, it recalculates the process pressure relief speed and adjusts control parameters in a timely manner, achieving a smooth transition of the pressure relief process curve and preventing instability or accidents.
Pressure relief to return stroke determination and valve reset: When the pressure is relieved to the process-set safe return pressure (usually below 5 MPa), the system stops pressure relief, and the cubic press switches to the fast return stroke process. To ensure continuous production and execution of the next process, the ultra-high pressure relief valve must close. The software records the output pulse amount during pressure relief. When switching from pressure relief to return stroke, it controls the servo motor to reverse, outputting the recorded pulse amount to the servo controller to achieve precise reset of the ultra-high pressure relief valve. This prevents valve core jamming or failure to open again, creating conditions for precise control in the next ultra-high pressure servo relief process.
Actual Application Results.
The servo control system has successfully undergone trial acceptance on DZ1000 and DZ800 forging cubic presses.
Test results show that during the process of ultra-high pressure relief from 100 MPa to a safe pressure of 3 MPa, the coincidence rate between the actual pressure relief speed curve and the process pressure relief speed curve reached over 95%, achieving smooth, linear, safe, and precise control of ultra-high pressure relief.
In terms of pressure relief speed, servo control technology can achieve linear control in a wide range of 0.01~0.5 MPa/s, which is particularly suitable for the slow pressure relief processes required for high-end super-hard material synthesis.
Although the application cost of servo control technology increased by 20% compared to stepping motors, its performance improved by more than double. It is also safer and more reliable, facilitating the synthesis of high-performance super-hard materials.