Created on:2022-03-09 13:13

Application of electro-hydraulic servo valve

Application of electro-hydraulic servo valve

Due to its high precision and fast control ability, electro-hydraulic servo valve is widely used in open-loop or closed-loop electro-hydraulic control systems of various industrial equipment such as machine tools, plastics, rolling mills and vehicles, in addition to the fields commonly used in aerospace and military equipment. Especially when the system requires high dynamic response and large output power, it has been widely used.

(1) Position control circuit of electro-hydraulic servo valve. Figure 172 shows the linear position circuit of hydraulic cylinder controlled by electro-hydraulic servo valve, figure 172 (a) shows its schematic diagram, and figure 172 (b) shows its functional block diagram. When the system inputs the command signal from the command potentiometer, the electromechanical converter of the electro-hydraulic servo valve 2 acts. After the energy is converted and amplified through the hydraulic amplifier (pilot stage and power stage), the pressure oil of the hydraulic source supplies oil to the hydraulic cylinder 3 through the electro-hydraulic servo valve to drive the load to the preset position, The feedback signal detected by the feedback potentiometer (position sensor) is compared with the input command signal through the servo amplifier 1 to make the actuator move at the required position with precision.

172

Figure 173 shows the linear position circuit controlled by the electro-hydraulic servo valve, figure 173 (a) shows its schematic diagram, and figure 173 (b) shows its functional block diagram. When the system inputs the command signal, it is amplified by energy conversion. The pressure oil of the hydraulic source supplies oil to the hydraulic motor 3 through the electro-hydraulic servo valve 2. The gear reducer 4 and the lead screw nut mechanism 5 convert the rotary motion of the motor into the linear motion of the load. The feedback signal detected by the position sensor is compared with the input command signal through the servo amplifier 1 to make the load precision move at the required position.

173

Figure 174 shows the angular position circuit of the hydraulic motor controlled by the electro-hydraulic servo valve, figure 174 (a) shows its schematic diagram, and figure 174 (b) shows its functional block diagram. It uses the white integer unit as the angle difference measuring device (three lines represent the outgoing line of stator winding, two lines represent the outgoing line of rotor winding, and the dotted line through the center of the circle represents the rotating shaft). The input shaft is connected with the transmitter shaft, and the output shaft is connected with the receiver. The synchro unit detects the angle insertion between the input shaft and the output shaft, and converts the angle difference into the amplitude modulation transition voltage signal. After being amplified by the AC amplifier and demodulated by the demodulator, the AC voltage signal is converted into the DC voltage signal, and then amplified by the servo power amplifier l to generate a differential current to control the electro-hydraulic servo valve 2. After the hydraulic energy is amplified, The pressure oil of the hydraulic source supplies oil to the hydraulic motor 3 through the electro-hydraulic servo valve 2. The motor drives the load to rotate through the gear reducer 4. After the above feedback signal is compared with the input command signal, the load moves accurately at the required corner position.

174

(2) Speed control circuit of electro-hydraulic servo valve. Fig. 175 shows the circuit that uses the electro-hydraulic servo valve to control the rotation speed of the two-way quantitative hydraulic motor to maintain a certain value. Fig. 175 (a) shows its schematic diagram and Fig. 175 (b) shows its functional block diagram. When the system inputs the command signal, the electro-mechanical converter of the electro-hydraulic servo valve 2 acts. After the energy is converted and amplified through the hydraulic amplifier (pilot stage and power stage), the pressure oil of the hydraulic source supplies oil to the two-way hydraulic motor 3 through the electro-hydraulic servo valve, so that the hydraulic motor drives the load to work at a certain speed; At the same time, the detection feedback signal UF of the speed measuring motor (speed sensor) 4 is compared with the input command signal through the servo amplifier 1, and the obtained error signal controls the valve opening of the electro-hydraulic servo valve, so as to keep the speed of the actuator near the set value.

175

Figure 176 shows the speed circuit of the hydraulic motor controlled by the open-loop variable displacement pump, figure 176 (a) shows its schematic diagram, and figure 176 (b) shows its functional block diagram. 5. The two-way quantitative hydraulic motor 6, the safety overflow valve group 7 and the oil make-up check valve group 8 form a closed oil circuit, which regulates the speed of the hydraulic motor 6 by changing the displacement of the variable displacement pump 5. The displacement adjustment of variable displacement pump is realized by the displacement adjustment of double rod hydraulic cylinder 3 controlled by electro-hydraulic servo valve 2. The actuator and load are open-loop with the hydraulic cylinder controlled by electro-hydraulic servo. When the system inputs the command signal, the pressure oil of the control hydraulic source supplies oil to the double rod hydraulic cylinder 3 through the electro-hydraulic servo valve 2, so that the variable mechanism of the hydraulic cylinder driving the variable pump works at a certain position; At the same time, the error signal obtained by comparing the detection feedback signal of the position sensor 4 with the input command signal through the servo amplifier 1 controls the valve opening of the electro-hydraulic servo valve, so as to keep the displacement of the variable mechanism of the variable pump, that is, the variable pump, near the set value, and finally ensure that the hydraulic motor 6 works near the desired speed value.

176

Figure 177 shows the speed circuit of the hydraulic motor controlled by the closed-loop variable displacement pump, figure 177 (a) shows its schematic diagram, and figure 177 (b) shows its functional block diagram. The oil circuit structure is basically the same as that of the hydraulic motor speed circuit controlled by the open-loop variable displacement pump shown in Figure 176. The difference is that a speed measuring motor (speed sensor) 9 is added between the load and command mechanism to form a closed-loop speed control circuit. Therefore, its speed control accuracy is higher.

177.178

(3) Force and pressure control circuit of electro-hydraulic servo valve. Figure 178 (a) shows the force control circuit of the electro-hydraulic servo valve. The oil source supplies oil to the double rod hydraulic cylinder 3 through the electro-hydraulic servo valve 2, and the force generated by the hydraulic cylinder is applied to the load. The detection feedback signal of the force sensor 4 is compared with the input command signal through the servo amplifier 1, and then the action of the cylinder is controlled through the electro-hydraulic servo valve, so as to keep the load force basically constant. Figure 178 (b) shows the control circuit to maintain the constant pressure difference between the two chambers of the double rod hydraulic cylinder. When the electro-hydraulic servo valve 2 receives the input command signal and converts and amplifies the signal, the pressure difference between the two chambers of the double rod hydraulic cylinder 3 reaches a certain set value. When the pressure in the cylinder changes, the detection feedback signal of the differential pressure sensor 5 controlled near the hydraulic cylinder is compared with the input signal command through the servo amplifier 1, and then the action of the cylinder is controlled through the electro-hydraulic servo valve, so as to keep the differential pressure between the two chambers of the hydraulic cylinder basically constant. Figure 178 (c) shows the functional block diagram of the force and pressure control circuit of the electro-hydraulic servo valve.

(4) Hydraulic cylinder synchronous control circuit of electro-hydraulic servo valve. Figure 179 shows the synchronous control circuit of hydraulic cylinder using electro-hydraulic servo valve to drain oil. The diverter valve 6 is used for rough synchronous control, and then the electro-hydraulic servo valve 5 performs bypass oil drainage according to the feedback signal of the position error detector (differential transformer) 3 to realize accurate synchronous control. The synchronization accuracy of the circuit is high (up to 0.2mm), and the position error of the two cylinders can be eliminated by itself; Rough synchronization can still be achieved in case of servo valve failure. The servo valve can use small flow valve to discharge oil, but the cost is high and the efficiency is low. It is suitable for occasions requiring high synchronization accuracy.

Fig. 180 shows a hydraulic cylinder synchronization control circuit tracked by an electro-hydraulic servo valve. The electro-hydraulic servo valve 1 controls the opening of the valve port and outputs the same flow as the directional valve 2, so that the two hydraulic cylinders can obtain two-way synchronous movement. The circuit has high synchronization accuracy, but the price is expensive. The utility model is suitable for occasions where the two hydraulic cylinders are far apart and require high synchronization accuracy.

Fig. 181 shows a synchronous control loop for flow distribution using an electro-hydraulic servo valve. The electro-hydraulic servo valve 2 continuously adjusts the opening of the valve port according to the feedback signals of the displacement sensors 4 and 5, and controls the input or output flow of the two hydraulic cylinders to make them obtain two-way synchronous movement. The characteristics of the circuit are the same as those shown in Figure 175.

180.181

2. Precautions for use

(1) Reasonably select electro-hydraulic servo valve. First, select the type of servo valve according to the system control type. Generally, for position or speed servo control system, flow type servo valve shall be selected; For force or pressure servo control system, pressure servo valve or flow servo valve shall be selected. Then, according to the performance requirements, select the appropriate type of electromechanical converter (moving iron type or moving coil type) and the stage of hydraulic amplifier (single-stage, two-stage or three-stage). The type selection of valves can refer to the characteristics of various valves and combined with the manufacturer's product catalogue or samples.

(2) Pay special attention to the filtration and cleaning of the oil circuit. A precision filter with a filtration accuracy of less than 5 µ m must be installed before entering the servo valve.

(3) After the installation of the whole hydraulic servo system, the oil circuit must be thoroughly cleaned before the servo valve is installed into the system. At the same time, observe the pollution of the filter element, and remove the filter after flushing for 24 ~ 36h.

(4) Before installing the servo valve, do not move the zero adjustment device at will.

(5) Welded connectors are not allowed for hydraulic pipelines. It is recommended to use connectors in the form of ferrule 24 ° cone structure.

(6) The installation surface of the servo valve shall be smooth, straight and clean.

(7) When installing the servo valve, check the following items.

1) Whether there is dirt on the installation surface and whether the oil inlet and outlet are connected properly? Are the O-rings intact? Is the dowel hole correct?

2) When installing the servo valve on the connecting plate, tighten the connecting screws evenly.

3) Before connecting the circuit, pay attention to check the terminal, and check the polarity after everything is normal.

(8) The oil tank of the servo system must be sealed and equipped with air filter and magnetic oil filter. The replacement of new oil must be subject to strict fine filtration (the filtration accuracy is less than 5 µ m).

(9) The hydraulic oil shall be changed regularly, once every half a year, and the oil shall be kept within the range of 40 ~ 50 ℃ as far as possible.

(10) The servo valve shall be used in strict accordance with the conditions specified in the manual. In case of system failure, first check and eliminate the links other than the circuit and servo valve, and then check the servo valve.

 

 

 

 

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