Test of hydraulic AGC servo cylinder of rolling mill
Test of hydraulic AGC servo cylinder of rolling mill
The hydraulic AGC system of rolling mill has become the core equipment of high-precision and fast rolling. The key component in the system - rolling servo hydraulic cylinder has large rolling force, short stroke, high frequency response and difficult test. It is often forced to stop production for maintenance because it is unable to predict the fault or judge the fault location.
According to the actual use of large-scale rolling mill, with reference to the relevant national and industrial hydraulic test standards, taking the rolling mill hydraulic AGC servo hydraulic cylinder as the test object, a unit has developed and designed a new set of large-scale rolling mill hydraulic AGC servo hydraulic cylinder test-bed equipment with a maximum rolling force of 9200 t, which mainly completes the dynamic and static performance test of the hydraulic cylinder.
The maximum rolling force of the test bench for the large mill is 9200t, and the hydraulic system diagram of the test bench is shown in Figure 25. The system consists of two parts: loading system and tested system.
The tested system is controlled by the force and position servo system on the right. The components used include test hydraulic cylinder 14, three-stage electro-hydraulic servo valve 3, oil pressure sensor 5, etc. The loading system is controlled by the force servo system on the left.
The test hydraulic cylinder system is an electro-hydraulic position control system with pressure feedback, and its schematic diagram is shown in Figure 26. The load pressure of the hydraulic cylinder measured by the pressure sensor is fed back to the input end after correction and amplification, forming an inner load pressure feedback loop. Because the pressure feedback increases the hydraulic natural frequency and damping ratio of the original open-loop transfer function, it is a good way to improve and produce constant damping.
The test-bed mainly completes the dynamic and static performance test of the hydraulic cylinder. The closed frame is used for loading the servo hydraulic cylinder during the dynamic test. During the test, the rodless cavity of the loading cylinder is filled with pressure oil to generate thrust, which will be tightly pressed on the frame by the tested servo hydraulic cylinder to simulate the rolling condition, and the displacement sensor is installed symmetrically. At the same time, the two hydraulic cylinders are supplied with oil, and the dynamic displacement of the tested servo cylinder is detected according to the displacement sensor on the tested hydraulic cylinder. The dynamic performance parameters of the hydraulic cylinder are obtained from the relationship between displacement and force.
The dynamic test principle of the servo hydraulic cylinder is as follows: in the dynamic test software environment, a group of harmonic voltage signals are given through the channel of the data acquisition card, converted into the corresponding harmonic current signals by the servo amplifier, sent to the servo valve coil, and the oil flow into the servo cylinder is controlled by controlling the displacement of the valve core. The servo cylinder converts the flow into displacement output, which is detected by the displacement sensor. The two channels of the data acquisition card enter the computer. Through the conversion and calculation of the two displacement signals, the steady-state output of the system can be obtained. The amplitude frequency characteristics and phase frequency characteristics of the test system can be obtained by comparing the input and output harmonic signals. The test hydraulic cylinder system is an electro-hydraulic position control system with pressure feedback. The simulation model of the test control system is established by using the Simulink simulation toolbox in MATLAB software, and the simulation analysis is carried out.
The simulation results obtained from Bode diagram are: the amplitude margin of the position feedback control system is 26.2db greater than 6dB, and the phase angle margin is 119 ° greater than 60 °. The system has good stability. After adding pressure feedback, the hydraulic natural frequency of the original open-loop transfer function is increased, and the damping ratio is increased. The damping ratio indicates the relative stability of the system. In order to obtain satisfactory performance, the value of hydraulic damping ratio should be increased. As the damping ratio of the system is increased, the amplitude margin reaches 28.4db, and the stability of the system is improved compared with the original system. The simulation results of step response diagram show that after adding pressure feedback, the transition time of the system increases from 0.301s to 0.321s, and the response speed decreases. Therefore, pressure feedback is a better method to improve and produce constant damping. Pressure feedback can significantly improve the damping ratio of the system without changing the open-loop and closed-loop stiffness of the system, thereby expanding the frequency band of the system, improving the control accuracy and increasing the stability of the system. However, the response speed of the system decreases, so a compromise between the damping ratio and rapidity of the system is needed.
The function configuration of the servo cylinder test control system of large rolling mill conforms to the actual and economic conditions of the rolling mill, and the comprehensive effect is good. It can save costs in production, improve the competitiveness of products, and provide a feasible test means for the localization of large heavy-duty servo cylinders.