Key points of using electro-hydraulic proportional valve
Key points of using electro-hydraulic proportional valve
(1) Electro hydraulic proportional pressure control. Using electro-hydraulic proportional pressure control can easily realize a certain pressure control law according to the requirements of production process and equipment load characteristics, and avoid pressure overshoot, oscillation and hydraulic shock caused by pressure control step change. Compared with the pressure control of traditional manual control valve, it can greatly simplify the control circuit and system, improve the control performance, and is more convenient for installation, use and maintenance. In the electro-hydraulic proportional pressure control circuit, it is controlled by proportional valve, proportional pump or motor, but the control circuit based on proportional pressure valve control is widely used.
1) Proportional voltage regulating circuit. The electro-hydraulic proportional relief valve can be used to form a proportional pressure regulating circuit. The system pressure can be set arbitrarily within the rated value by changing the input electrical signal of the proportional relief valve.
There are two basic forms of pressure regulating circuit composed of electro-hydraulic proportional overflow valve. First, as shown in Figure 158 (a), a direct acting electro-hydraulic proportional relief valve 2 is connected with the remote control port of the traditional pilot relief valve 3. The proportional relief valve 2 is used for remote proportional pressure regulation, while the traditional pilot relief valve 3 not only acts as the main overflow, but also acts as the safety valve of the system. Second, as shown in Figure 158 (b), the pilot electro-hydraulic proportional relief valve 5 is directly used to proportional regulate the system pressure. When the input electrical signal of the proportional relief valve 5 is zero, the system can be unloaded. The traditional direct acting overflow valve 6 installed at the remote control port of valve 5 can prevent excessive fault current input from causing high pressure and damaging the system.
Like the electro-hydraulic proportional pressure regulating circuit, there are two basic forms of pressure reducing circuit composed of electro-hydraulic proportional pressure reducing valve. First, as shown in Figure 159 (a), a direct acting electro-hydraulic proportional pressure valve 3 is connected with the pilot remote control port of the traditional pilot pressure reducing valve 4, and the proportional pressure valve 3 is used as the set pressure of the remote control pressure reducing valve 4, so as to realize the hierarchical pressure transformation control of the system; The maximum working pressure of 1 is set by overflow valve 2. Second, as shown in Figure 159 (b), the pilot electro-hydraulic proportional reducing valve 7 is directly used to reduce the system pressure, and the maximum working pressure of hydraulic pump 5 is set by overflow valve 6.
(2) Electro hydraulic proportional speed control. Using electro-hydraulic proportional flow valve (throttle valve or speed regulating valve) control can easily realize a certain speed control law according to the requirements of production process and equipment load characteristics. Compared with the speed control of traditional manual control valve, it can greatly simplify the control circuit and system, improve the control performance, and is more convenient for installation, use and maintenance.
2) Electro hydraulic proportional control circuit for micro feed of machine tool. Figure 161 shows the schematic diagram of the electro-hydraulic proportional control circuit of the micro feed of the machine tool. The traditional speed regulating valve L and electro-hydraulic proportional speed regulating valve 3 are used to realize the micro feed of the machine tool workbench driven by the hydraulic cylinder 2. The movement speed of the hydraulic cylinder is determined by its flow Q2 (Q2 = q1-q3). When Q1 > Q3, the piston moves to the left; When Q1 ＜ Q3, the piston moves to the right, so the piston movement can be reversed without a reversing valve. The advantages of this control mode are: the small feed can be obtained by using the proportional speed regulating valve with small flow gain, instead of using the small flow speed regulating valve; Both speed regulating valves can work under large opening (flow) and are not easy to be blocked; Both open-loop control and closed-loop control can be used to ensure that the output speed of the hydraulic cylinder is constant or changes according to the set law. If the traditional speed regulating valve 1 is replaced by the proportional speed regulating valve, the speed regulating range can also be expanded.
(3) Electro hydraulic proportional direction speed control. The electro-hydraulic proportional directional valve or (high-performance electro-hydraulic proportional directional valve) with both directional control and flow proportional control function can realize the reversing and speed proportional control of the hydraulic system. Several examples are given below.
1) Electro hydraulic proportional control circuit of automatic welding line lifting device. Figure 162 (a) shows the operating speed cycle diagram of the lifting device of the automatic welding line. The maximum speed of lifting and lowering is required to reach 0.5m/s, and the speed at the midpoint of the lifting stroke shall not exceed 0.15m/s. Therefore, the electro-hydraulic proportional control circuit of the lifting device composed of electro-hydraulic proportional direction throttle valve 1 and electronic proximity switch 2 (so-called analog trigger) is adopted, as shown in Figure 162 (H). During operation, as the piston block gradually approaches the switch 2, the analog voltage output by the proximity switch will be reduced until ov, and the electro-hydraulic proportional direction valve will be controlled through the proportional amplifier to make the hydraulic cylinder 5 change the horizontal displacement into vertical lifting movement through the four-bar mechanical converter according to the requirements of the running speed cycle diagram. This loop is quite effective for large inertia load controlling position repetition accuracy.
2) Electro hydraulic proportional control system for docking manipulator of deep submergence lifeboat. In the process of rescuing the wrecked submarine, it is necessary to connect the deep submarine lifeboat with the wrecked boat, establish a life channel, and transport the personnel in the wrecked boat to the lifeboat to complete the rescue task. There are two pairs of docking manipulators in the lifeboat, which is an important executive device of the lifeboat and has local autonomous function. Figure 163 shows its docking principle (only one pair of manipulators is given). When the deep submergence lifeboat 1 stays above the wreck 9 according to certain requirements, through the local autonomous control of the docking manipulator driven by four symmetrically distributed hydraulic cylinders, complete the three-step docking operation process, such as the initial connection between the manipulator and the wreck docking skirt 7, the automatic alignment between the lifeboat docking skirt 7 and the wreck docking skirt, and tightening the manipulator to make the two pairs of docking skirts connect correctly, In order to solve the docking problem between the lifeboat and the wrecked boat by the dynamic positioning system of the lifeboat which is difficult to approach directly due to factors such as wind, wave and current and the inclination of the wrecked boat. In order to avoid damaging the manipulator due to the inertial impact force of a 50t lifeboat, a compression spring buffer 4 is set between the pre claws of the telescopic arm, and the hydraulic cylinder of the arm is controlled through computer feedback to reduce the contact force between the Claw 5 and the deck; At the same time, the electro-hydraulic proportional system is used to control the manipulator to make it have compliance function.
Figure 164 shows the principle of the electro-hydraulic proportional control system of the manipulator (only the control circuit of one manipulator is shown in the figure, and the control circuits of the other three manipulators are the same). The actuator of the system is the hydraulic cylinder 10 and hydraulic cylinder 11 that realize the two degrees of freedom of the docking manipulator swing and expansion, and the hydraulic cylinder 12 that drives the claw opening and closing. The two degrees of freedom of swing and expansion adopt the electro-hydraulic proportional directional valves 5 and 6 with flow regulation function to realize the closed-loop position control, and the two position four-way electromagnetic directional valves 8 and 9 combine to realize the compliance control of the arm. The movement of the gripper cylinder 12 is controlled by the electro-hydraulic proportional directional valve 7. The oil source of the system is quantitative hydraulic pump 1, and its oil supply pressure is set by overflow valve 3. Check valve 2 is used to prevent the oil from pouring back to the hydraulic pump, and 4 is used to isolate the oil circuit of claw cylinder 12 and the other two cylinders to prevent mutual interference.
Taking telescopic cylinder 11 as an example, the control principle of the system is as follows. When the electromagnet 6ya is energized to switch the directional valve 9 to the left position, the telescopic hydraulic cylinder will be connected with the proportional valve 6. At this time, the input electrical signal law of the proportional electromagnets 3YA and 4ya can be controlled through the proportional controller of the valve 6, and the position control of the hydraulic cylinder piston can be realized, and the system works in the position follow-up state. When 6ya is powered off and one of 3YA and 4ya is powered on, the rodless cavity and the rodless cavity of hydraulic cylinder 11 are connected through the y-function of directional valve 9 and connected with the return oil of the system, so that the two cavities of hydraulic cylinder are unloaded, and the piston rod can move freely with the movement of load to realize the flexible function of expansion and contraction. This can not only ensure the initial connection between the manipulator and the target ring on the wrecked boat, but also create conditions for the docking of the other three manipulators. The fork can buffer the inertial force caused by the movement of the lifeboat and avoid damaging the manipulator. The control principle of the swing hydraulic cylinder circuit is similar to that of the telescopic cylinder.
The characteristics of the system are: the compliance function of the manipulator is realized through the cooperation control of electro-hydraulic proportional directional valve and; By setting buffer device and electro-hydraulic proportional ring control, the docking manipulator of deep submergence lifeboat will not be damaged by inertial impact, and the success rate of docking is improved.
2. Precautions for use
(1) When selecting proportional throttle valve or proportional directional valve, it must be noted that the power domain (working limit) of electro-hydraulic proportional throttle valve or proportional directional valve cannot be exceeded.
(2) Pay attention to control oil pollution. The oil pollution degree of proportional valve is usually required to be grade 7 ~ 9 of nasl638 (grade 16 / 13, 17 / 14 and 18 / 15 of ISO). The main link of this index is the pilot level. Although the anti pollution ability of electro-hydraulic proportional valve is stronger than that of servo valve, it can not take oil pollution lightly, because many faults of electro-hydraulic proportional control system are also caused by oil pollution.
(3) The proportional valve must be matched with the amplifier. Generally, the proportional amplifier can be supplied with the proportional valve. The amplifier generally has deep current negative feedback, and the flutter current is superimposed in the signal current. The amplifier is designed to keep the valve core in the original position or minimize the system pressure when the power is off or the differential transformer is disconnected, so as to ensure safety. A ramp signal generator is sometimes set in the amplifier to control the boost, depressurization time or motion acceleration or deceleration. The amplifier driving the proportional directional valve often has a function generator to compensate for large dead time characteristics.
The distance between the proportional valve and the proportional amplifier can be up to 60m, and the distance between the signal source and the amplifier can be arbitrary.
(4) The traditional methods to control acceleration and deceleration include: switching time delay of directional valve, end position buffer in hydraulic cylinder, electronically controlled flow valve and variable displacement pump. Using proportional directional valve and slope signal generator can provide a good solution, which can improve the cycle speed of the machine and prevent inertial impact.