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1 Introduction When the decanter centrifuge is working, the drum speed and the speed difference between the drum and the screw pusher determine the material separation effect and output, etc., and are important variable parameters of the centrifuge shed. At present, the driving method of domestic centrifuges is usually relatively single. The most commonly used driving method is a dual-motor structure, that is, one motor directly drives the drum to rotate through a belt, and the other motor drives the spiral through a reducer. This driving method generally has shortcomings such as poor reliability and stability, short service life, low separation capability, poor separation accuracy, and poor adaptability to changes in physical properties. The use of hydraulic drive has advantages that other drive methods cannot match, such as larger drive torque, simpler speed difference control method and lower speed difference. This article combines the advantages of hydraulic transmission and adopts fully closed-loop control of the speed of two motors to achieve arbitrary adjustment of the drum speed and speed difference; it can also improve reliability and stability through appropriate control methods; it also improves separation accuracy and adaptability to changes in physical properties. 2 Design of the decanter centrifuge hydraulic system 1) Working principle of the decanter centrifuge hydraulic system According to the functional requirements of the decanter centrifuge, the designed hydraulic system schematic diagram is shown in Figure h. This system consists of three parts: the main transmission circuit, the control circuit and the oil supply circuit. 2) The main transmission circuit of the hydraulic system of the decanter centrifuge. The main transmission circuit uses a variable pump and a certain amount of motor volume speed regulation circuits. There are two circuits: one is mainly composed of a variable pump 1 and a motor 13. The motor is connected to the screw pusher, and the variable pump n drives the motor 13 to rotate, driving the screw pusher to work; the other is composed of the variable pump 21 and the motor 19, the motor 19 is connected to the drum, and the variable pump 21 drives the motor 19 to rotate, driving the drum to rotate at high speed. Among them, the safety valves 12 and 20 play the role of overload protection. By changing the displacement of the variable pumps 11 and 21, the output speeds of the drum and the screw pusher can be controlled respectively. 3) The control circuit of the hydraulic system of the decanter centrifuge mainly consists of the control oil provided by the pump 2 passing through the high-pressure filter 3 and the electro-hydraulic proportional directional valves 7 and 26 to the two cavities of the double-rod cylinders 9 and 23 of the variable pump respectively; by changing the input current of the electro-hydraulic proportional directional valve 26 to control the position of the double-rod cylinders 9 and 23, the purpose of adjusting the displacement of the variable pumps 11 and 21 is achieved, and ultimately the output speed of the drum and screw pusher is adjusted. 4) The oil supply circuit of the Chenbo centrifuge hydraulic system is mainly composed of the oil supply pump 32, one-way valves 27, 30, relief valves 16, 24 and the cooler 35. The oil charge pump 32 supplies oil to the low-pressure side of the transmission circuit, and the excess oil flows to the cooler 35 through the relief valves 16 and 24 and is discharged back to the oil tank. The main function is to replenish oil and cool the main transmission circuit. 3 Decanter centrifuge hydraulic system control strategy From an overall point of view, the decanter centrifuge hydraulic system mainly adjusts the output speed of the screw pusher and the drum by controlling the input voltage of the electro-hydraulic proportional directional valves 7 and 26 respectively. However, due to load changes, the main oil line pressure fluctuates, causing system leakage and unstable output flow, resulting in unstable output speeds of the spiral pusher and drum, which affects the separation effect of the decanter separator. Therefore, according to the separation accuracy requirements, the parameter output of the speed control is obtained from the rotational speed sensor, which forms a closed-loop control with the input voltage to achieve the purpose of real-time control of the decanter centrifuge drum speed and the output speed of the screw pusher, improve the stability of the system, enhance the anti-interference ability of the system, and achieve a satisfactory output speed. The control principle block diagram of the decanter centrifuge hydraulic system is shown in Figure lb. The values that need to be displayed are the input drum speed vl and the speed difference △2 between the drum and the screw pusher. 4 Mathematical model of the hydraulic control system of the decanter centrifuge It can be seen from Figure lb that this system is actually two sets of closed-loop control systems. By controlling the output speed of the drum and the screw pusher respectively, the system drum output speed and the speed difference between the drum and the screw pusher are determined. During the design, considering the interchangeability of the system, the hardware selection of the two systems is consistent, so the open-loop transfer functions of the two closed-loop control systems are the same; however, due to the difference in their loads, the simulation results of the transfer functions are different. According to the system hydraulic schematic diagram and system control block diagram, the open-loop transfer function of the closed-loop control system can be established. 1) Mathematical model of pump-controlled motor The mathematical model of pump-controlled motor is composed of rotating drum (or screw pusher), quantitative motor and variable pump. The transfer function is: 4) Block diagram of the closed-loop control system of the hydraulic system of the Chenbo centrifuge. The block diagram of the closed-loop control system of the hydraulic system of the decanter centrifuge is shown in Figure 2. By substituting each parameter into Figure Za, the block diagram of the closed-loop control system of the drum and the block diagram of the closed-loop control system of the screw pusher can be obtained respectively. Specifically shown in Figure Zb and Figure ZC. 5. Simulation analysis of the hydraulic drive system of the decanter centrifuge. The input step signal is 25 mV. The dynamic characteristics of the control system are simulated through the Simuhnk software package provided by Matlab. The results are shown in Figure 3. It can be seen from Figure 3 that the closed-loop step response curve of the control system has no overshoot and has good stability, but the rise time is long. This is mainly due to the large inertia of the system. Therefore, this system can meet the actual needs of the centrifuge; if the control effect of the control system is changed, it can be further corrected to achieve better performance requirements. 6 Conclusion (1) The designed new type of hydraulically driven decanter centrifuge overcomes the shortcomings of the traditional drive method and improves the separation accuracy of the system and the adaptability to changes in physical properties; (2) The system simulation results show that the system stability is good, but the rise time is long due to the large system inertia. However, according to actual industrial and mining, this system can fully meet the actual needs of the centrifuge; (3) The designed hydraulic drive system provides a platform for seeking better control strategies to meet higher demands. Figure 3 Time domain simulation of decanter centrifuge closed-loop control system References: (1) Yuan Huixin Separation Engineering [M]. Beijing: Sinopec Press, 2001. (2) Cao Zhiwei. Analysis of technical differences between domestic and imported decanter centrifuges Mechanical and Electronics, 2004 (12).