A control system for a pressure maintaining tool

Abstract

The application discloses a kind of control systems of pressure maintaining tool, comprising: system oil circuit, first clamp oil circuit and second clamp oil circuit, first clamp oil circuit and second clamp oil circuit are connected in parallel, and all with system oil circuit is connected, system oil circuit includes hydraulic pump, electromagnetic reversing valve, throttle valve and pressure maintaining valve group, first clamp oil circuit includes first clamp oil cylinder and two first sequence valves, second clamp oil circuit includes second clamp oil cylinder and two second sequence valves, wherein, the opening pressure of first sequence valve is less than the opening pressure of second sequence valve, hydraulic pump is connected with first sequence valve and second sequence valve simultaneously by electromagnetic reversing valve, throttle valve and pressure maintaining valve group, when reaching the opening pressure of first sequence valve, hydraulic oil enters first clamp oil cylinder, controls first clamp oil cylinder to work, when reaching the opening pressure of second sequence valve, hydraulic oil enters second clamp oil cylinder again, controls second clamp oil cylinder to work, realizes the automatic control of order.

Description

Technical Field

[0001] This invention relates to the technical field of fixture control, and more particularly to a control system for a pressure-holding fixture. Background Technology

[0002] During the use of pressure holding fixtures, the oil pipes need to be manually inserted and removed. Since there are many oil pipes in multi-circuit fixtures, and the fixtures also have sequential requirements, manual insertion and removal is inefficient and the sequence is prone to errors, which can easily lead to product deformation or even fixture damage. Summary of the Invention

[0003] In view of the above-mentioned shortcomings of the prior art, the technical problem to be solved by the present invention is to propose a control system for a pressure holding fixture, which can control each fixture to move in sequence, with high control precision and higher efficiency.

[0004] To achieve the above objectives, this utility model provides a control system for a pressure-holding fixture, including a system oil circuit, a first clamp oil circuit, and a second clamp oil circuit. The first clamp oil circuit and the second clamp oil circuit are connected in parallel and are both connected to the system oil circuit. The system oil circuit includes a hydraulic pump. The first clamp oil circuit includes a first clamp cylinder and a first sequence valve. The second clamp oil circuit includes a second clamp cylinder and a second sequence valve. The first sequence valve has a first opening pressure, and the second sequence valve has a second opening pressure. The first opening pressure is less than the second opening pressure.

[0005] The hydraulic pump is connected to both the first sequence valve and the second sequence valve. When the pressure of the hydraulic oil provided by the hydraulic pump is greater than the first opening pressure, the hydraulic oil provided by the hydraulic pump can enter the first clamp cylinder through the first sequence valve. When the pressure of the hydraulic oil provided by the hydraulic pump is greater than the second opening pressure, the hydraulic oil provided by the hydraulic pump can enter the second clamp cylinder through the second sequence valve.

[0006] The first sequence valve is provided in two parts, and the two first sequence valves are respectively connected to the rod chamber and the rodless chamber of the first clamping cylinder. The second sequence valve is provided in two parts, and the two second sequence valves are respectively connected to the rod chamber and the rodless chamber of the second clamping cylinder.

[0007] The hydraulic pump is simultaneously connected to two of the first sequence valves and two of the second sequence valves;

[0008] The system oil circuit also includes a solenoid directional valve, a throttle valve, a pressure holding valve group, and an oil tank. The solenoid directional valve is equipped with a first electromagnet and a second electromagnet.

[0009] When the first electromagnet is energized, the hydraulic pump is connected to the rodless chamber of the first clamp cylinder in sequence through the electromagnetic reversing valve, the throttle valve, the pressure holding valve group and one of the first sequence valves, and is connected to the rodless chamber of the second clamp cylinder in sequence through the electromagnetic reversing valve, the throttle valve, the pressure holding valve group and another of the second sequence valves. The rod chambers of both the first clamp cylinder and the second clamp cylinder are connected to the oil tank through the pressure holding valve group and the electromagnetic reversing valve.

[0010] When the second electromagnet is energized, the hydraulic pump is connected to the rod chamber of the first clamp cylinder in sequence through the electromagnetic reversing valve, the pressure holding valve group, and one of the first sequence valves, and is connected to the rod chamber of the second clamp cylinder in sequence through the electromagnetic reversing valve, the pressure holding valve group, and the other second sequence valve. The rodless chambers of the first clamp cylinder and the second clamp cylinder are both connected to the oil tank through the pressure holding valve group, the throttle valve, and the electromagnetic reversing valve.

[0011] According to the control system of the pressure-holding fixture described above, the first clamp oil circuit further includes a first adjustable pressure reducing valve and two first check valves. One of the first sequential valves is connected to the rodless chamber of the first clamp cylinder through the first adjustable pressure reducing valve. One port of the first check valve is connected to the rodless chamber of the first clamp cylinder, and the other port of the first check valve is connected to the pressure-holding valve group. One port of the other first check valve is connected to the rod chamber of the second clamp cylinder, and the other port of the first check valve is connected to the pressure-holding valve group. The opening directions of the two first check valves are both facing the pressure-holding valve group.

[0012] According to the control system of the pressure-holding fixture described above, the second clamping oil circuit further includes a second adjustable pressure-reducing valve and two second check valves. The two second sequential valves are connected to the rodless chamber of the second clamping cylinder through the second adjustable pressure-reducing valve. One port of one of the second check valves is connected to the rodless chamber of the second clamping cylinder, and the other port of the second check valve is connected to the pressure-holding valve group. One port of the other second check valve is connected to the rod chamber of the second clamping cylinder, and the other port of the second check valve is connected to the pressure-holding valve group. The opening directions of the two second check valves are both facing the pressure-holding valve group.

[0013] According to the control system of the pressure-holding fixture described above, an overflow valve is provided between the hydraulic pump and the electromagnetic directional valve.

[0014] The control system of the pressure holding fixture described above further includes a third clamping oil circuit and a fourth clamping oil circuit. The first clamping oil circuit, the second clamping oil circuit, the third clamping oil circuit and the fourth clamping oil circuit are connected in parallel. The third clamping oil circuit includes a third clamping oil cylinder and a third sequence valve. The fourth clamping oil circuit includes a fourth clamping oil cylinder and a fourth sequence valve.

[0015] Both the third sequence valve and the fourth sequence valve are connected to the hydraulic pump. The third sequence valve has a third opening pressure, and the fourth sequence valve has a fourth opening pressure. The third opening pressure is greater than the second opening pressure, and the fourth opening pressure is greater than the third opening pressure.

[0016] The control system of the pressure holding fixture described above also includes an accumulator, which is used to replenish oil for the first clamping cylinder, the second clamping cylinder, the third clamping cylinder and the fourth clamping cylinder.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: When the first electromagnet of the electromagnetic reversing valve is energized, the hydraulic oil from the hydraulic pump enters the first clamp cylinder through the relief valve, electromagnetic reversing valve, throttle valve, pressure holding valve group, first sequence valve, and first adjustable pressure reducing valve. At the same time, after flowing through the pressure holding valve group, it can enter the second clamp cylinder through the second sequence valve and second adjustable pressure reducing valve. By setting the opening pressure of the first and second sequence valves, the hydraulic oil can first enter the rodless chamber in the first clamp cylinder and drive the piston rod to move towards the rod chamber side. At this time, the clamp performs the advancing action. When the hydraulic oil pressure reaches the opening pressure of the second sequence valve, the hydraulic oil controls the second clamp cylinder to move. The two clamps clamp in sequence, which can avoid operational errors. At the same time, the flow rate of the hydraulic oil can be controlled by the throttle valve, thereby controlling the action time of the clamp and achieving precise control. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the control system of the present invention.

[0019] In the picture:

[0020] 1. System oil circuit; 11. Hydraulic pump; 12. Relief valve; 13. Solenoid directional valve; 131. First electromagnet; 132. Second electromagnet; 14. Throttle valve; 15. Pressure holding valve assembly;

[0021] 2. First clamping hydraulic circuit; 21. First clamping hydraulic cylinder; 22. First sequence valve; 23. First adjustable pressure reducing valve; 24. First check valve;

[0022] 3. Second clamp hydraulic circuit; 31. Second clamp hydraulic cylinder; 32. Second sequence valve; 33. Second adjustable pressure reducing valve; 34. Second check valve;

[0023] 4. Third clamp hydraulic circuit; 41. Third clamp hydraulic cylinder; 42. Third sequence valve;

[0024] 5. Fourth clamp hydraulic circuit; 51. Fourth clamp hydraulic cylinder; 52. Fourth sequence valve;

[0025] 6. Accumulator. Detailed Implementation

[0026] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0027] Please refer to Figure 1 This invention discloses a control system for a pressure-holding fixture, comprising a system oil circuit 1, a first clamping oil circuit 2, and a second clamping oil circuit 3, i.e., at least two clamping oil circuits. The first clamping oil circuit 2 and the second clamping oil circuit 3 are connected in parallel and are both connected to the system oil circuit 1. The system oil circuit 1 includes a hydraulic pump 11, the first clamping oil circuit 2 includes a first clamping cylinder 21 and a first sequence valve 22, and the second clamping oil circuit 3 includes a second clamping cylinder 31 and a second sequence valve 32. The first sequence valve 22 is provided with a first opening pressure, and the second sequence valve 32 is provided with a second opening pressure. The opening pressure is less than the second opening pressure. That is, the hydraulic oil provided by the system oil circuit 1 can simultaneously supply the first clamp oil circuit 2 and the second clamp oil circuit 3. Since their hydraulic oil is supplied by the same hydraulic pump 11 and is located in the same oil circuit, their pressure values ​​are the same. When the hydraulic pump 11 continuously supplies oil, the pressure of the hydraulic oil in its oil circuit continues to increase until it reaches the first opening pressure or even the second opening pressure. The hydraulic oil can control the first clamp cylinder 21 to work through the first sequence valve 22 and control the second clamp cylinder 31 to work through the second sequence valve 32.

[0028] Hydraulic pump 11 is connected to both the first sequence valve 22 and the second sequence valve 32. When the pressure of the hydraulic oil provided by hydraulic pump 11 is greater than the first opening pressure, the hydraulic oil provided by hydraulic pump 11 can enter the first clamp cylinder 21 through the first sequence valve 22. When the pressure of the hydraulic oil provided by hydraulic pump 11 is greater than the second opening pressure, the hydraulic oil provided by hydraulic pump 11 can enter the second clamp cylinder 31 through the second sequence valve 32. By setting the opening pressure of the sequence valves, the requirement for the first clamp cylinder 21 and the second clamp cylinder 31 to move sequentially can be met, thus achieving automatic control of the sequence.

[0029] Preferably, there are two first sequence valves 22, which are respectively connected to the rod chamber and rodless chamber of the first clamping cylinder 21. There are also two second sequence valves 32, which are respectively connected to the rod chamber and rodless chamber of the second clamping cylinder 31. The hydraulic pump 11 is connected to both first sequence valves 22 and two second sequence valves 32. That is, whether the hydraulic oil supplied by the hydraulic pump 11 enters the rod chamber or rodless chamber of the first clamping cylinder 21, it must pass through the first sequence valve 22. When entering the second clamping cylinder 31, it must pass through the second sequence valve 32. Therefore, when the first clamping cylinder 21 and the second clamping cylinder 31 drive the clamp to move forward and backward, they follow a strict sequence.

[0030] More preferably, the system oil circuit 1 further includes an electromagnetic directional valve 13, a throttle valve 14, a pressure holding valve group 15, and an oil tank. The electromagnetic directional valve 13 is equipped with a first electromagnet 131 and a second electromagnet 132. The electromagnetic directional valve 13 is provided with an oil inlet, an oil outlet, a first oil port, and a second oil port. When the first electromagnet 131 is energized, the oil inlet connected to the hydraulic pump 11 is connected to the first oil port. At this time, the high-pressure oil provided by the hydraulic pump 11 can enter the rodless chamber of the first clamping cylinder 21 and the second clamping cylinder 31. When the second electromagnet 132 is energized, the oil inlet is connected to the second oil port. At this time, the high-pressure oil provided by the hydraulic pump 11 can enter the rod-side chamber of the first clamping cylinder 21 and the second clamping cylinder 31. The specific flow path is as follows:

[0031] When the first electromagnet 131 is energized, the hydraulic pump 11 connects sequentially to the rodless chamber of the first clamping cylinder 21 via the solenoid directional valve 13, the throttle valve 14, the pressure holding valve assembly 15, and one of the first sequence valves 22. It also connects sequentially to the rodless chamber of the second clamping cylinder 31 via the same solenoid directional valve 13, throttle valve 14, pressure holding valve assembly 15, and another second sequence valve 32. The rod chambers of both the first and second clamping cylinders 21 are connected to the oil tank via the pressure holding valve assembly 15 and the solenoid directional valve 13. When the first electromagnet 131 is energized, the high-pressure hydraulic oil supplied by the hydraulic pump 11 enters the first clamping cylinder 21 in sequence. In the rodless chamber of the second clamping cylinder 31, the piston rod is driven to move towards the rod chamber side. At this time, the clamping action is performed, and the hydraulic oil in the rod chambers of the first clamping cylinder 21 and the second clamping cylinder 31 returns to the oil tank. The throttle valve 14 can control the oil supply flow of the hydraulic pump 11, and thus control the time when the hydraulic oil in the oil circuit reaches the first starting pressure and the second starting pressure, and thus control the sequential interval time to achieve precise control. The pressure holding valve group 15 can be used to provide pressure holding for the hydraulic oil supplied by the hydraulic pump 11.

[0032] When the second electromagnet 132 is energized, the hydraulic pump 11 connects to the rod chamber of the first clamp cylinder 21 via the electromagnetic directional valve 13, the pressure holding valve group 15, and one of the first sequence valves 22, and connects to the rod chamber of the second clamp cylinder 31 via the electromagnetic directional valve 13, the pressure holding valve group 15, and another second sequence valve 32. The rodless chambers of the first clamp cylinder 21 and the second clamp cylinder 31 are connected to the oil tank via the pressure holding valve group 15, the throttle valve 14, and the electromagnetic directional valve 13. When the second electromagnet 132 is energized, the hydraulic pump 11 connects to the rod chambers of the first clamp cylinder 21 and the second clamp cylinder 31. When it supplies oil to the rod chambers of the first clamp cylinder 21 and the second clamp cylinder 31, it drives the piston rod to move towards the rodless chamber side. At this time, the clamp retracts, and the hydraulic oil in the rodless chambers of the first clamp cylinder 21 and the second clamp cylinder 31 returns to the oil tank.

[0033] More preferably, the first clamping oil circuit 2 further includes a first adjustable pressure reducing valve 23 and two first check valves 24, one of which is a first sequence valve 22 connected to the first clamping oil cylinder 21 via the first adjustable pressure reducing valve 23. The rodless chamber of the first clamping cylinder 21 is connected to the rodless chamber of the first clamping cylinder 21, and the other port of the first check valve 24 is connected to the pressure holding valve assembly 15. One port of the other first check valve 24 is connected to the rod chamber of the second clamping cylinder 31, and the other port of the first check valve 24 is connected to the pressure holding valve assembly 15. The openings of both first check valves 24 face the pressure holding valve assembly 15. In this embodiment, both the first sequence valve 22 and the first adjustable pressure reducing valve 23 are adjustable. The first sequence valve 22 can adjust its opening pressure, and the first adjustable pressure reducing valve 23 can adjust its pressure reducing range. The first adjustable pressure reducing valve 23 ensures that the pressure value inside the first clamping cylinder 21 is within the normal range, thus protecting the first clamping cylinder 21. One of the first check valves 24 is connected in parallel to the second clamping cylinder 31. On one side of the first sequence valve 22 with the rod chamber connected, another first check valve 24 is connected in parallel on one side of the series oil circuit of the first adjustable pressure reducing valve 23 and the first sequence valve 22. Since the openings of the two first check valves 24 are facing the pressure holding valve group 15, when the hydraulic oil moves to the first clamp cylinder 21, it cannot pass through the first check valve 24, but can only pass through the first sequence valve 22. When the hydraulic oil in the first clamp cylinder 21 is discharged, it can return through the first check valve 24 without passing through the first sequence valve 22.

[0034] More preferably, the second clamping oil circuit 3 further includes a second adjustable pressure reducing valve 33 and two second check valves 34. One second sequence valve 32 is connected to the rodless chamber of the second clamping cylinder 31 via the second adjustable pressure reducing valve 33. One port of one second check valve 34 is connected to the rodless chamber of the second clamping cylinder 31, and the other port of the second check valve 34 is connected to the pressure holding valve assembly 15. One port of the other second check valve 34 is connected to the rod chamber of the second clamping cylinder 31. Another oil port is connected to the pressure holding valve group 15. The opening direction of the two second check valves 34 is facing the pressure holding valve group 15. In this embodiment, the second sequence valve 32 and the second adjustable pressure reducing valve 33 are both adjustable. The second sequence valve 32 can adjust its opening pressure, and the second adjustable pressure reducing valve 33 can adjust its pressure reducing range, which plays a role in protecting the second clamping cylinder 31. One of the second check valves 34 is connected in parallel to the second sequence valve 32 on the side of the rod chamber of the second clamping cylinder 31. The other second check valve 34 is connected in parallel to the second adjustable pressure reducing valve 33 and the other sequence valve on the same side. Similarly, when oil is entering, oil enters through the second sequence valve 32, and when oil is returning, oil returns through the second check valve 34.

[0035] More preferably, a relief valve 12 is provided between the hydraulic pump 11 and the solenoid directional valve 13. The relief valve 12 is used to protect the overall oil circuit. If the oil pressure in the oil circuit is too high, the oil can be unloaded through the relief valve 12.

[0036] Preferably, the system further includes a third clamping oil circuit 4 and a fourth clamping oil circuit 5. The first clamping oil circuit 2, the second clamping oil circuit 3, the third clamping oil circuit 4, and the fourth clamping oil circuit 5 are connected in parallel. The third clamping oil circuit 4 includes a third clamping oil cylinder 41 and a third sequence valve 42, and the fourth clamping oil circuit 5 includes a fourth clamping oil cylinder 51 and a fourth sequence valve 52. Both the third sequence valve 42 and the fourth sequence valve 52 are connected to the hydraulic pump 11. The third sequence valve 42 is provided with a third opening pressure, and the fourth sequence valve 52 is provided with a fourth opening pressure. The third opening pressure is greater than the second opening pressure, and the fourth opening pressure is greater than the third opening pressure. That is, in this embodiment, a total of four clamping oil circuits are provided. By controlling the opening pressure of the sequence valves, each clamping oil circuit can be opened and operated in sequence. Of course, three, five, or even more clamping oil circuits can also be selected to achieve the same effect, which should not exceed the protection scope.

[0037] More preferably, it also includes an accumulator 6, which is used to replenish oil for the first clamp cylinder 21, the second clamp cylinder 31, the third clamp cylinder 41 and the fourth clamp cylinder 51. That is, the accumulator 6 is used to replenish oil for the entire oil circuit. If a certain clamp cylinder or other valve body leaks, the presence of the accumulator 6 can ensure the normal operation of the entire oil circuit.

[0038] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0039] Furthermore, in this invention, descriptions involving terms such as "first," "second," and "a" are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0040] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0041] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

Claims

1. A control system for a pressure-holding fixture, characterized in that, The system includes a system oil circuit, a first clamp oil circuit, and a second clamp oil circuit. The first clamp oil circuit and the second clamp oil circuit are connected in parallel and are both connected to the system oil circuit. The system oil circuit includes a hydraulic pump. The first clamp oil circuit includes a first clamp cylinder and a first sequence valve. The second clamp oil circuit includes a second clamp cylinder and a second sequence valve. The first sequence valve has a first opening pressure, and the second sequence valve has a second opening pressure. The first opening pressure is less than the second opening pressure. The hydraulic pump is connected to both the first sequence valve and the second sequence valve. When the pressure of the hydraulic oil provided by the hydraulic pump is greater than the first opening pressure, the hydraulic oil provided by the hydraulic pump can enter the first clamp cylinder through the first sequence valve. When the pressure of the hydraulic oil provided by the hydraulic pump is greater than the second opening pressure, the hydraulic oil provided by the hydraulic pump can enter the second clamp cylinder through the second sequence valve. The first sequence valve is provided in two parts, and the two first sequence valves are respectively connected to the rod chamber and the rodless chamber of the first clamping cylinder. The second sequence valve is provided in two parts, and the two second sequence valves are respectively connected to the rod chamber and the rodless chamber of the second clamping cylinder. The hydraulic pump is simultaneously connected to two of the first sequence valves and two of the second sequence valves; The system oil circuit also includes a solenoid directional valve, a throttle valve, a pressure holding valve group, and an oil tank. The solenoid directional valve is equipped with a first electromagnet and a second electromagnet. When the first electromagnet is energized, the hydraulic pump is connected to the rodless chamber of the first clamp cylinder in sequence through the electromagnetic reversing valve, the throttle valve, the pressure holding valve group and one of the first sequence valves, and is connected to the rodless chamber of the second clamp cylinder in sequence through the electromagnetic reversing valve, the throttle valve, the pressure holding valve group and another of the second sequence valves. The rod chambers of both the first clamp cylinder and the second clamp cylinder are connected to the oil tank through the pressure holding valve group and the electromagnetic reversing valve. When the second electromagnet is energized, the hydraulic pump is connected to the rod chamber of the first clamp cylinder in sequence through the electromagnetic reversing valve, the pressure holding valve group, and one of the first sequence valves, and is connected to the rod chamber of the second clamp cylinder in sequence through the electromagnetic reversing valve, the pressure holding valve group, and the other second sequence valve. The rodless chambers of the first clamp cylinder and the second clamp cylinder are both connected to the oil tank through the pressure holding valve group, the throttle valve, and the electromagnetic reversing valve.

2. The control system for a pressure-holding fixture according to claim 1, characterized in that, The first clamp oil circuit further includes a first adjustable pressure reducing valve and two first check valves. One of the first sequential valves is connected to the rodless chamber of the first clamp cylinder through the first adjustable pressure reducing valve. One port of the first check valve is connected to the rodless chamber of the first clamp cylinder, and the other port of the first check valve is connected to the pressure holding valve group. One port of the other first check valve is connected to the rod chamber of the second clamp cylinder, and the other port of the first check valve is connected to the pressure holding valve group. The openings of both first check valves face the pressure holding valve group.

3. The control system for a pressure-holding fixture according to claim 1, characterized in that, The second clamping oil circuit also includes a second adjustable pressure reducing valve and two second check valves. The two second sequence valves are connected to the rodless chamber of the second clamping cylinder through the second adjustable pressure reducing valve. One port of one of the second check valves is connected to the rodless chamber of the second clamping cylinder, and the other port of the second check valve is connected to the pressure holding valve group. One port of the other second check valve is connected to the rod chamber of the second clamping cylinder, and the other port of the second check valve is connected to the pressure holding valve group. The openings of the two second check valves are both facing the pressure holding valve group.

4. The control system for a pressure-holding fixture according to claim 1, characterized in that, An overflow valve is provided between the hydraulic pump and the electromagnetic reversing valve.

5. The control system for a pressure-holding fixture according to claim 1, characterized in that, It also includes a third clamping oil circuit and a fourth clamping oil circuit. The first clamping oil circuit, the second clamping oil circuit, the third clamping oil circuit and the fourth clamping oil circuit are connected in parallel. The third clamping oil circuit includes a third clamping oil cylinder and a third sequence valve. The fourth clamping oil circuit includes a fourth clamping oil cylinder and a fourth sequence valve. Both the third sequence valve and the fourth sequence valve are connected to the hydraulic pump. The third sequence valve has a third opening pressure, and the fourth sequence valve has a fourth opening pressure. The third opening pressure is greater than the second opening pressure, and the fourth opening pressure is greater than the third opening pressure.

6. The control system for a pressure-holding fixture according to claim 5, characterized in that, It also includes an accumulator, which is used to replenish oil for the first clamp cylinder, the second clamp cylinder, the third clamp cylinder and the fourth clamp cylinder.

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