Ultrahigh-pressure multipoint synchronous jacking hydraulic system and control method

Abstract

The ultrahigh-pressure multi-point synchronous jacking hydraulic system comprises a servo motor, an ultrahigh-pressure plunger pump, an unloading valve, a safety valve, N control valve sets and N jacking oil cylinders, and N is larger than or equal to 2; the servo motor drives the ultrahigh-pressure plunger pump to provide a pressure oil source, the N control valve sets can independently control lifting and pressure maintaining of the corresponding jacking oil cylinders, and when synchronous errors occur due to uneven loads in the lifting process of the four jacking oil cylinders, load compensation is achieved by adjusting the pressure of the proportional overflow valves in the control valve sets. And high-precision jacking oil cylinder synchronous control can be realized. The proportional valves are adopted to perform pressure compensation on loads of all the oil cylinders, the oil cylinders fast in action do not need to stop to wait for the oil cylinders slow in action in the synchronous control process, frequent switching of the switching valves is avoided, and synchronous, stable and high-precision control can be achieved through the system and the control method.

Description

Technical Field

[0001] The present invention relates to the field of hydraulic drive and control, and in particular to an ultra-high pressure multi-point synchronous jacking hydraulic system and a control method. Background Art

[0002] Ultra-high-pressure hydraulic jacking systems are widely used in the installation of large-scale projects such as bridges, buildings, and power facilities. In order to ensure the accuracy of installation and docking, multiple jacking cylinders need to be controlled synchronously. Most 35MPa-level hydraulic synchronous jacking systems use proportional flow valves or servo valves to adjust the flow of each group of cylinders, but there are no corresponding products on the market for 70MPa-level ultra-high-pressure proportional flow valves or servo valves.

[0003] Currently, most ultra-high-pressure synchronous jacking systems use electromagnetic on-off valves for control. Because the loads at the lifting points of multiple cylinders can vary significantly, resulting in uneven speeds across the cylinders, when the displacement of a particular jacking cylinder exceeds the set deviation, the electromagnetic reversing valve closes, disconnecting the oil from the cylinder. The faster cylinder stops and waits for the slower one. When the deviation falls below the set value, the solenoid valve reopens, and the cylinder resumes its movement. The disadvantages of this solution are the frequent switching of the solenoid valve, low synchronization accuracy of the on-off valve control, and pressure surges in the oil pipe when the on-off valve is switched. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention proposes an ultra-high pressure multi-point synchronous jacking hydraulic system and a control method thereof, which has high control accuracy and strong versatility.

[0005] The purpose of the present invention is achieved through the following technical solutions: An ultra-high pressure multi-point synchronous jacking hydraulic system, comprising a servo motor, an ultra-high pressure plunger pump, an unloading valve, a safety valve, N control valve groups and N jacking cylinders, N ≥ 2; The servo motor drives the ultra-high pressure plunger pump to rotate and discharge hydraulic oil; The oil ports at both ends of the unloading valve and the safety valve are respectively connected to the outlet oil circuit and the oil tank of the ultra-high pressure plunger pump; the unloading valve is a normally open structure, which can unload the system in the power-off state; N control valve groups and N lifting cylinders are connected one by one; Each of the control valve groups includes a solenoid reversing valve, a balancing valve, a first one-way valve, a second one-way valve, a proportional relief valve and four groups of oil ports C, D, E, and F; the oil port C is connected to the outlet oil circuit of the ultra-high pressure plunger pump, the oil port D is connected to the oil tank, the oil port E is connected to the large chamber of the corresponding jacking cylinder, and the oil port F is connected to the small chamber of the corresponding jacking cylinder; the solenoid reversing valve is a three-position four-way solenoid reversing valve, including P port, T port, A port, and B port, and the middle position function is "Y" type. The P port of the solenoid reversing valve is connected to the oil port C , port T is connected to the oil port D, port A is connected to the forward oil inlet of the balancing valve, and port B is connected to the reverse oil port of the first one-way valve; the reverse oil inlet of the balancing valve is connected to the oil port E, and the control oil port of the balancing valve is connected to the reverse oil port of the first one-way valve; the forward oil port of the first one-way valve is connected to the oil return port of the proportional relief valve; the reverse oil port of the second one-way valve is connected to the oil port F, and the forward oil port is connected to the reverse oil port of the first one-way valve; the oil inlet of the proportional relief valve is connected to the oil port F; When the electromagnetic reversing valve is in a neutral state, the balancing valve can lock the lifting cylinder that bears the load and maintain the pressure.

[0006] Furthermore, the ultra-high pressure plunger pump is a radial plunger pump.

[0007] Furthermore, the unloading valve is a two-position two-way electromagnetic stop valve.

[0008] Furthermore, the safety valve is a manual overflow valve structure.

[0009] Furthermore, the lifting cylinder is a double-acting cylinder, and a displacement sensor is installed on each cylinder.

[0010] Furthermore, the maximum output pressure of the ultra-high pressure plunger pump is greater than the set pressure of the safety valve.

[0011] A control method for an ultra-high pressure multi-point synchronous jacking hydraulic system, wherein the process of controlling the raising of a single jacking cylinder is as follows: The servo motor drives the ultra-high pressure plunger pump to rotate and discharge hydraulic oil, the safety valve is energized, the unloading circuit is closed, and the electromagnetic reversing valve is switched to the left position, so that the P port is connected with the A port, and the B port is connected with the T port; the outlet oil of the ultra-high pressure plunger pump passes through the P port and the A port of the electromagnetic reversing valve and the one-way valve in the balancing valve, and enters the large chamber of the jacking cylinder, pushing the piston of the jacking cylinder to extend upward, and the small chamber oil of the jacking cylinder returns to the oil tank through the proportional relief valve, the first one-way valve, the B port and the T port of the electromagnetic reversing valve; the current of the proportional relief valve is kept at 0, and the upward extension speed of the piston of the jacking cylinder is controlled by adjusting the speed of the servo motor.

[0012] Furthermore, the process of controlling the descent of a single lifting cylinder is as follows: When the safety valve is energized, the unloading circuit is closed, and the electromagnetic reversing valve is switched to the right position, so that the P port is connected to the B port and the A port is connected to the T port; the outlet oil of the ultra-high pressure plunger pump enters the small chamber of the jacking cylinder through the P port, B port and the second one-way valve of the electromagnetic reversing valve. When the pressure in the small chamber is greater than the opening pressure of the balancing valve, the piston of the jacking cylinder retracts downward, and the large chamber oil of the jacking cylinder returns to the oil tank through the balancing valve, the A port and the T port of the electromagnetic reversing valve; the current of the proportional relief valve is kept at 0, and the descending speed of the piston of the jacking cylinder is controlled by adjusting the speed of the servo motor.

[0013] Furthermore, the control process of synchronous lifting of N lifting cylinders is as follows: The servo motor drives the ultra-high pressure plunger pump to rotate and discharge hydraulic oil, the safety valve is energized, the unloading circuit is closed, and the electromagnetic reversing valves in all control valve groups are switched to the left position, so that the P port is connected to the A port and the B port is connected to the T port; the current of all proportional relief valves is set to 0; When there is uneven load on the four groups of jacking cylinders, the oil will preferentially enter the jacking cylinder with smaller load, causing the jacking cylinder with light load to move faster and the jacking cylinder with heavy load to move slower; according to the value fed back by the displacement sensor of each group of jacking cylinders, the current of the proportional relief valve in the control valve group corresponding to the jacking cylinder with the smallest displacement is set to 0, and the current of the proportional relief valve corresponding to the remaining faster jacking cylinders is adjusted, and PID control is performed according to the displacement difference to increase the current; the current of the proportional relief valve increases, which increases the return oil pressure of the small cavity of the corresponding jacking cylinder, thereby compensating the load pressure of the jacking cylinder under low load, resulting in a decrease in the oil originally entering the jacking cylinder with faster oil, and a decrease in the rising speed of the corresponding jacking cylinder; since the oil flow rate discharged by the ultra-high pressure plunger pump is fixed, the oil entering other jacking cylinders increases, and the corresponding jacking speed increases, thereby reducing the piston displacement deviation of each jacking cylinder; High-precision displacement control of N jacking cylinders is achieved by adjusting the current of each proportional relief valve in real time.

[0014] Furthermore, by setting the rotation speed of the servo motor, the average speed at which the pistons of the N lifting cylinders rise synchronously is adjusted.

[0015] The beneficial effects of the present invention are as follows: 1. The present invention adopts a proportional relief valve to control the pressure of the oil return chamber of the oil cylinder, and the proportional valve pressure does not need to be ultra-high pressure.

[0016] 2. The present invention performs synchronous adjustment through a proportional relief valve. During the adjustment process, the oil cylinder does not need to stop and wait, and the oil cylinder moves smoothly.

[0017] 3. During the synchronous adjustment process of the present invention, there is no need to frequently switch the reversing valve, thereby avoiding pressure shock during reversing.

[0018] 4. The present invention adjusts the cylinder speed in real time through a proportional relief valve, which is simple to control and has high synchronization accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a hydraulic principle diagram of the ultra-high pressure four-point synchronous jacking system according to an embodiment of the present invention.

[0020] Figure 2 2 is a hydraulic principle diagram of the first control valve group in an embodiment of the present invention.

[0021] Figure 3 This is a diagram of the oil circuit status during the rising process of a single lifting cylinder in an embodiment of the present invention.

[0022] Figure 4 This is a diagram of the oil circuit status during the descending process of a single lifting cylinder in an embodiment of the present invention.

[0023] In the figure, 1 is the servo motor, 2 is the ultra-high pressure plunger pump, 3 is the unloading valve, 4 is the safety valve, 5 is the first control valve group, 6 is the second control valve group, 7 is the third control valve group, 8 is the fourth control valve group, 9 is the first lifting cylinder, 10 is the second lifting cylinder, 11 is the third lifting cylinder, 12 is the fourth lifting cylinder, 5.1 is the electromagnetic reversing valve, 5.2 is the balancing valve, 5.3 is the first one-way valve, 5.4 is the second one-way valve, and 5.5 is the proportional relief valve. DETAILED DESCRIPTION

[0024] The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments, and the purpose and effects of the present invention will become more apparent. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] like Figure 1 As shown, taking four-point synchronous jacking as an example, the ultra-high pressure multi-point synchronous jacking system of an embodiment of the present invention includes a servo motor 1, an ultra-high pressure plunger pump 2, an unloading valve 3, a safety valve 4, a first control valve group 5, a second control valve group 6, a third control valve group 7, a fourth control valve group 8, a first jacking cylinder 9, a second jacking cylinder 10, a third jacking cylinder 11, and a fourth jacking cylinder 12.

[0026] The servo motor 1 drives the ultra-high pressure plunger pump 2 to rotate and discharge hydraulic oil. The flow rate of the discharged hydraulic oil can be controlled by adjusting the speed of the servo motor 1. In this embodiment, the ultra-high pressure plunger pump 2 is a radial plunger pump with a maximum output pressure greater than 70 MPa.

[0027] The unloading valve 3 is a two-position two-way electromagnetic stop valve, and the oil ports at both ends are respectively connected to the outlet oil circuit and the oil tank of the ultra-high pressure plunger pump 2; the unloading valve 3 is a normally open structure, which can unload the ultra-high pressure system in the power-off state.

[0028] The safety valve 4 is a manual overflow valve structure, with its inlet connected to the outlet of the ultra-high pressure plunger pump 2 and its outlet connected to the oil tank, and the set pressure is 70 MPa.

[0029] The first control valve group 5 includes a group of electromagnetic reversing valves, a group of balancing valves, two groups of one-way valves, a group of proportional relief valves and four groups of oil ports C, D, E, and F. The oil port C is connected to the outlet oil circuit of the ultra-high pressure plunger pump 2, the oil port D is connected to the return oil from the oil tank, the oil port E is connected to the large chamber (rodless chamber) of the first lifting cylinder 9, and the oil port F is connected to the small chamber (rod chamber) of the cylinder.

[0030] The oil ports C and D of the second control valve group 6, the third control valve group 7, and the fourth control valve group 8 are respectively connected to the outlet oil circuit and the oil tank of the ultra-high pressure plunger pump 2, the oil port E of the second control valve group 6 is connected to the large cavity of the second lifting cylinder 10, and the oil port F is connected to the small cavity of the cylinder, the oil port E of the third control valve group 7 is connected to the large cavity of the third lifting cylinder 11, and the oil port F is connected to the small cavity of the cylinder, the oil port E of the fourth control valve group 8 is connected to the large cavity of the fourth lifting cylinder 12, and the oil port F is connected to the small cavity of the cylinder.

[0031] The first lifting cylinder 9, the second lifting cylinder 10, the third lifting cylinder 11 and the fourth lifting cylinder 12 have the same structure, are double-acting cylinders, and are equipped with displacement sensors.

[0032] like Figure 2 As shown, the first control valve group 5 includes a solenoid reversing valve 5.1, a balancing valve 5.2, a first check valve 5.3, a second check valve 5.4, and a proportional relief valve 5.5. The solenoid reversing valve 5.1 is a three-position, four-way solenoid reversing valve with a "Y"-type neutral position function. Port P of the reversing valve is connected to port C of the control valve group, port T is connected to port D of the control valve group, port A is connected to the forward oil inlet of the balancing valve 5.2, port B is connected to the reverse oil port of the first check valve 5.3, the reverse oil inlet of the balancing valve 5.2 is connected to port E of the control valve group, the control oil port is connected to the reverse oil port of the first check valve 5.3, the forward oil port of the first check valve 5.3 is connected to the oil return port of the proportional relief valve 5.5, the reverse oil port of the second check valve 5.4 is connected to port F of the control valve group, the forward oil port is connected to the reverse oil port of the first check valve 5.3, and the oil inlet of the proportional relief valve 5.5 is connected to port F of the control valve group. When the electromagnetic reversing valve 5.1 is in the neutral state, the pressure at the control port of the balancing valve 5.2 is 0, and the one-way valve in the balancing valve 5.2 can lock the jacking cylinder that bears the load and maintain the pressure.

[0033] The composition and internal connection method of the second control valve group 6 , the third control valve group 7 , and the fourth control valve group 8 are the same as those of the first control valve group 5 .

[0034] like Figure 3 As shown, the process for controlling the piston's ascent in the first lift cylinder 9 is as follows: servo motor 1 drives ultra-high-pressure plunger pump 2 to rotate and discharge hydraulic oil. Safety valve 3 is energized, closing the unloading circuit and switching solenoid reversing valve 5.1 to the left, connecting port P with port A and port B with port T. Oil from the pump's outlet flows through ports P and A of the solenoid reversing valves and the check valve inside balancing valve 5.2, entering the large chamber of the first lift cylinder 9 and pushing the piston upward. Oil in the small chamber of the first lift cylinder 9 then flows through proportional relief valve 5.5, first check valve 5.3, and ports B and T of the solenoid reversing valve 5.1, returning to the tank. When a single cylinder is operating, the current flowing through proportional relief valve 5.5 in all control valve groups remains at zero. The cylinder's ascent speed is controlled by adjusting the speed of servo motor 1. The process for controlling the corresponding loading valve groups when controlling the ascent of the remaining individual lift cylinders is identical to that for controlling the ascent of the first lift cylinder 9.

[0035] like Figure 4 As shown, the process for controlling the piston descent of the first jacking cylinder 9 is as follows: safety valve 3 is energized, the unloading circuit is closed, and the solenoid reversing valve 5.1 is switched to the right position, connecting ports P with B and ports A with T. Oil at the pump outlet flows through ports P and B of the solenoid reversing valves and the second check valve 5.4 into the small chamber of the first jacking cylinder 9. When the pressure in the small chamber exceeds the opening pressure of the balancing valve 5.2, the piston retracts downward, and the oil in the large chamber of the cylinder returns to the tank through the balancing valve 5.2 and ports A and T of the solenoid reversing valve 5.1. When a single cylinder is operating, the current flowing through the proportional relief valves in all control valve groups remains at zero. The speed of the jacking cylinder piston can be controlled by adjusting the speed of servo motor 1. The process for controlling the corresponding loading valve groups when controlling the descent of the remaining individual jacking cylinders is identical to that for controlling the descent of the first jacking cylinder 9.

[0036] The control process of synchronous lifting of four groups of lifting cylinders is as follows: servo motor 1 drives ultra-high pressure plunger pump 2 to rotate and discharge hydraulic oil, safety valve 3 is energized, unloading circuit is closed, electromagnetic reversing valves in all control valve groups are switched to left position, and currents of all proportional relief valves are set to 0; when there is uneven load among the four groups of lifting cylinders, oil will preferentially enter the lifting cylinder with smaller load, resulting in fast speed of low-load cylinder and slow speed of high-load cylinder. According to the value fed back by the displacement sensor of each group of lifting cylinders, the current of proportional relief valve in the control valve group corresponding to the lifting cylinder with the smallest displacement is kept at 0, and the current of the other faster cylinders is kept at 0. The proportional relief valve current corresponding to each cylinder is adjusted, and PID control is used to increase the current based on the displacement difference. This increase in proportional relief valve current increases the return oil pressure of the corresponding cylinder's small chamber, thereby compensating for the load pressure of the lifting cylinder under low load. This reduces the amount of oil entering the faster cylinder and reduces the corresponding cylinder's rising speed. Since the oil flow rate discharged by ultra-high pressure plunger pump 2 is fixed, the amount of oil entering the slower cylinder increases, increasing the lifting speed of the slow cylinder and reducing the piston displacement deviation of each cylinder. By adjusting the current of each proportional relief valve in real time, high-precision displacement control of the four cylinder groups can be achieved. By setting the speed of servo motor 1, the average speed of the synchronous rise of the four lifting cylinders can be adjusted.

[0037] This embodiment is only one of the implementation methods. After installing more control valve groups and jacking cylinders, the ultra-high pressure multi-point synchronous jacking hydraulic system and control method proposed in the present invention are also applicable to synchronous jacking systems with more jacking points.

[0038] Those skilled in the art will understand that the foregoing descriptions are merely preferred embodiments of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art will still be able to modify the technical solutions described in the foregoing examples or substitute equivalents for some of the technical features therein. Any modifications, equivalent substitutions, etc. made within the spirit and principles of the invention shall be included within the scope of protection of the invention.

Claims

1. An ultra-high pressure multi-point synchronous jacking hydraulic system, characterized in that: Including servo motor, ultra-high pressure plunger pump, unloading valve, safety valve, N control valve groups and N jacking cylinders, N ≥ 2; The servo motor drives the ultra-high pressure plunger pump to rotate and discharge hydraulic oil; The oil ports at both ends of the unloading valve and the safety valve are respectively connected to the outlet oil circuit and the oil tank of the ultra-high pressure plunger pump; the unloading valve is a normally open structure, which can unload the system in the power-off state; N control valve groups and N lifting cylinders are connected one by one; Each of the control valve groups includes a solenoid reversing valve, a balancing valve, a first one-way valve, a second one-way valve, a proportional relief valve and four groups of oil ports C, D, E and F; the oil port C is connected to the outlet oil circuit of the ultra-high pressure plunger pump, the oil port D is connected to the oil tank, the oil port E is connected to the large chamber of the corresponding jacking cylinder, and the oil port F is connected to the small chamber of the corresponding jacking cylinder; the solenoid reversing valve is a three-position four-way solenoid reversing valve, including port P, port T, port A and port B, and the middle position function is "Y" type. The P port of the solenoid reversing valve is connected to the oil port C , port T is connected to the oil port D, port A is connected to the forward oil inlet of the balancing valve, and port B is connected to the reverse oil port of the first one-way valve; the reverse oil inlet of the balancing valve is connected to the oil port E, and the control oil port of the balancing valve is connected to the reverse oil port of the first one-way valve; the forward oil port of the first one-way valve is connected to the oil return port of the proportional relief valve; the reverse oil port of the second one-way valve is connected to the oil port F, and the forward oil port is connected to the reverse oil port of the first one-way valve; the oil inlet of the proportional relief valve is connected to the oil port F; When the electromagnetic reversing valve is in a neutral state, the balancing valve can lock the lifting cylinder that bears the load and maintain the pressure.

2. The ultra-high pressure multi-point synchronous jacking hydraulic system according to claim 1, characterized in that: The ultra-high pressure plunger pump is a radial plunger pump.

3. The ultra-high pressure multi-point synchronous jacking hydraulic system according to claim 1, characterized in that: The unloading valve is a two-position two-way electromagnetic stop valve.

4. The ultra-high pressure multi-point synchronous jacking hydraulic system according to claim 1, characterized in that: The safety valve is a manual overflow valve structure.

5. The ultra-high pressure multi-point synchronous jacking hydraulic system according to claim 1, characterized in that: The lifting cylinders are double-acting cylinders, each of which is equipped with a displacement sensor.

6. The ultra-high pressure multi-point synchronous jacking hydraulic system according to claim 1, characterized in that: The maximum output pressure of the ultra-high pressure plunger pump is greater than the set pressure of the safety valve.

7. A control method for an ultra-high pressure multi-point synchronous jacking hydraulic system according to claim 1, characterized in that: The process of controlling the rise of a single lifting cylinder is as follows: The servo motor drives the ultra-high pressure plunger pump to rotate and discharge hydraulic oil, the safety valve is energized, the unloading circuit is closed, and the electromagnetic reversing valve is switched to the left position, so that the P port is connected with the A port, and the B port is connected with the T port; the outlet oil of the ultra-high pressure plunger pump passes through the P port and the A port of the electromagnetic reversing valve and the one-way valve in the balancing valve, and enters the large chamber of the jacking cylinder, pushing the piston of the jacking cylinder to extend upward, and the small chamber oil of the jacking cylinder returns to the oil tank through the proportional relief valve, the first one-way valve, the B port and the T port of the electromagnetic reversing valve; the current of the proportional relief valve is kept at 0, and the upward extension speed of the piston of the jacking cylinder is controlled by adjusting the speed of the servo motor.

8. The control method of the ultra-high pressure multi-point synchronous jacking hydraulic system according to claim 7, characterized in that: The process of controlling the descent of a single lifting cylinder is as follows: When the safety valve is energized, the unloading circuit is closed, and the electromagnetic reversing valve is switched to the right position, so that the P port is connected to the B port and the A port is connected to the T port; the outlet oil of the ultra-high pressure plunger pump enters the small chamber of the jacking cylinder through the P port, B port and the second one-way valve of the electromagnetic reversing valve. When the pressure in the small chamber is greater than the opening pressure of the balancing valve, the piston of the jacking cylinder retracts downward, and the large chamber oil of the jacking cylinder returns to the oil tank through the balancing valve, the A port and the T port of the electromagnetic reversing valve; the current of the proportional relief valve is kept at 0, and the descending speed of the piston of the jacking cylinder is controlled by adjusting the speed of the servo motor.

9. The control method of the ultra-high pressure multi-point synchronous jacking hydraulic system according to claim 8, characterized in that: The control process of synchronous lifting of N lifting cylinders is as follows: The servo motor drives the ultra-high pressure plunger pump to rotate and discharge hydraulic oil, the safety valve is energized, the unloading circuit is closed, and the electromagnetic reversing valves in all control valve groups are switched to the left position, so that the P port is connected to the A port and the B port is connected to the T port; the current of all proportional relief valves is set to 0; When the loads on the four lifting cylinders are uneven, the oil will preferentially flow into the lighter-loaded lifting cylinder, causing the lighter-loaded lifting cylinder to move faster and the heavier-loaded lifting cylinder to move slower. Based on the values fed back by the displacement sensors of each lifting cylinder group, the current of the proportional relief valve in the control valve group corresponding to the lifting cylinder with the smallest displacement is set to 0, and the current of the proportional relief valves corresponding to the remaining faster lifting cylinders is adjusted. PID control is performed based on the displacement difference to increase the current. The proportional relief valve current increases, causing the return oil pressure of the small chamber of the corresponding jacking cylinder to increase, thereby compensating the load pressure of the jacking cylinder under low load, resulting in a decrease in the oil entering the jacking cylinder that originally had oil flowing faster, and the corresponding lifting speed of the jacking cylinder is reduced; because the oil flow rate discharged by the ultra-high pressure plunger pump is fixed, the oil entering the other jacking cylinders increases, the corresponding jacking speed is increased, and the piston displacement deviation of each jacking cylinder is reduced; High-precision displacement control of N jacking cylinders is achieved by adjusting the current of each proportional relief valve in real time.

10. The control method of the ultra-high pressure multi-point synchronous jacking hydraulic system according to claim 9, characterized in that: By setting the rotation speed of the servo motor, the average speed at which the pistons of the N lifting cylinders rise synchronously is adjusted.

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