A servo hydraulic pad electro-hydraulic system and control method

Abstract

The present invention discloses a servo hydraulic pad electro-hydraulic system and a control method, wherein the servo hydraulic pad electro-hydraulic system mainly comprises a three-way control valve, a first shuttle valve, a support cartridge valve, a pilot electromagnetic ball valve, a first safety valve, a second shuttle valve, a second safety valve, a hydraulic pad displacement sensor, a first pressure sensor, a hydraulic cylinder, a cylinder displacement sensor, an accumulator, a second pressure sensor, a controller, etc. The system of the present invention has a fast dynamic response speed, realizes the synchronization of the multi-axis driven hydraulic pad and the coordinated control of the blank holding force, and the blank holding force is established quickly and stably with small fluctuations during the stretching process.

Description

Technical Field

[0001] The invention relates to an electro-hydraulic system and a control method of a hydraulic cushion, in particular to an electro-hydraulic system and a control method of a servo hydraulic cushion. Background Art

[0002] Hydraulic pads are commonly used blank holder force control devices in the metal sheet stretching process. The blank holder force directly determines the quality of the stretched workpiece. The blank holder force is passively generated by the forced movement of the hydraulic pad. The formation process is complicated, often accompanied by impact, and difficult to control. With the development of the stretching process, not only is the blank holder force required to be established in a short time and accurately controllable, but it is even required to automatically change according to a certain rule as the metal stretching state develops. How to control the hydraulic pad to achieve automatic control of the blank holder force, improve the response speed, and at the same time alleviate the impact generated when the mold and the hydraulic pad contact during the stretching process is a technical problem that needs to be solved urgently in the hydraulic pad stretching process. Summary of the invention

[0003] The purpose of the present invention is to provide an electro-hydraulic system and control method for a servo hydraulic pad, which can realize accurate dynamic automatic control of the pressure relief force of the hydraulic pad, not only quickly establish the pressure relief force, but also greatly alleviate the impact during the pressure relief force formation process.

[0004] The technical solution of the present invention is as follows:

[0005] A servo hydraulic pad electro-hydraulic system and control method, characterized in that: the servo hydraulic pad electro-hydraulic system mainly includes a three-way control valve, a first shuttle valve, a support cartridge valve, a pilot electromagnetic ball valve, a first safety valve, a second shuttle valve, a second safety valve, a hydraulic pad displacement sensor, a first pressure sensor, a hydraulic cylinder, a cylinder displacement sensor, an accumulator, a second pressure sensor, and a controller; wherein the three-way control valve, the first shuttle valve, the support cartridge valve, the pilot electromagnetic ball valve, the first safety valve, the second shuttle valve, the second safety valve, the first pressure sensor, the hydraulic The cylinder, cylinder displacement sensor, accumulator, and second pressure sensor form a group of electro-hydraulic drive shafts. The hydraulic cushion is driven by four groups of electro-hydraulic drive shafts. The hydraulic cylinders of the four groups of electro-hydraulic drive shafts are respectively installed at the four corners of the hydraulic cushion; the P port of the three-way control valve is connected with the A port of the first shuttle valve, the oil inlet of the second safety valve, the rod chamber of the hydraulic cylinder, the oil port of the accumulator, the detection port of the second pressure sensor, and the main oil source; the A port of the three-way control valve is connected with the A port of the support cartridge valve; the B port of the support cartridge valve is connected with the oil inlet of the first safety valve, the A port of the second shuttle valve, The detection port of the first pressure sensor is connected to the rodless chamber of the hydraulic cylinder, the B port of the first shuttle valve is connected to the control oil X port of the three-way control valve and the pilot control oil source, the C port of the first shuttle valve is connected to the B port of the second shuttle valve, the C port of the second shuttle valve is connected to the P port of the pilot electromagnetic ball valve, the A port of the pilot electromagnetic ball valve is connected to the control chamber of the support cartridge valve, the hydraulic oil tank is connected to the T port and the control oil Y port of the three-way control valve, the T port of the pilot electromagnetic ball valve, the oil outlet of the first safety valve, and the oil outlet of the second safety valve; the detection end of the hydraulic pad displacement sensor is connected to the Installed on the hydraulic pad, the cylinder displacement sensor detection end is built into the hydraulic cylinder, the controller is electrically connected with the three-way control valve amplifier, the pilot electromagnetic ball valve electromagnet, the hydraulic pad displacement sensor circuit, the first pressure sensor circuit, the cylinder displacement sensor circuit, and the second pressure sensor circuit; the first shuttle valve and the second shuttle valve connect the pilot control oil source, the main oil source and the highest pressure in the rodless chamber of the hydraulic cylinder to the P port of the pilot electromagnetic ball valve. When the pilot electromagnetic ball valve loses power, the support cartridge valve is effectively cut off; the hydraulic pad displacement sensor detects the displacement of the hydraulic pad sc , and convert it into an electrical signal and transmit it to the controller, which can calculate the speed of the hydraulic pad v.c. ; The first pressure sensor detects the rodless chamber pressure of the hydraulic cylinder Dad , and convert it into an electrical signal and transmit it to the controller; the cylinder displacement sensor detects the displacement of the hydraulic cylinder in , and convert it into an electrical signal and transmit it to the controller, which can calculate the speed of the hydraulic cylinder wow ; The second pressure sensor detects the rod chamber pressure of the hydraulic cylinder Pb , and convert it into an electrical signal and transmit it to the controller; the controller receives the sensor signal, executes the control algorithm, and converts the control command into an electrical signal to control the hydraulic valve; the flow coefficient of the three-way control valve is kv ; The effective area of ​​the rodless chamber of the hydraulic cylinder is Ah, the effective area of ​​the rod cavity is Ab .

[0006] Furthermore, the control method of the servo hydraulic pad electro-hydraulic system described in the present invention is characterized by comprising at least the following steps:

[0007] Hydraulic pad lifting: After the last stretching is completed, the hydraulic pad needs to be lifted to the initial setting position. During this process, the pilot electromagnetic ball valve is energized, and the A port and B port of the support cartridge valve are connected in both directions. The three-way control valve works in the working position of P port to A port. The hydraulic oil from the main oil source enters the rodless cavity of the hydraulic cylinder, and the hydraulic cylinder piston rod extends. The hydraulic circuit recycles the hydraulic oil flowing out of the rod cavity of the hydraulic cylinder, thereby reducing the rated input flow of the system, reducing the installed power, and saving energy; the controller uses the displacement of the hydraulic pad sc ,speed v.c. and displacement of the hydraulic cylinder in ,speed wow Calculate control instructions, control the three-way control valve to adjust the speed of the hydraulic cylinder and hydraulic pad and make the final positioning; control instructions include motion control instructions oh and synchronous leveling control instructions ul Assume that the desired trajectory of the hydraulic pad is scd ,but oh for:

[0008]

[0009] mPID Is to let the motion error escape , evc The smallest possible PID control function. oh Let the hydraulic pad move along the desired trajectory.

[0010] ul The calculation formula is:

[0011]

[0012] θ x , θ y They are the inclination angles of the hydraulic pad in the front-back and left-right directions respectively. lPID Yes θ x , θ y The smallest possible PID control function. ul Make four groups of hydraulic axes move synchronously.

[0013] The control signal of the three-way control valve when the hydraulic pad is lifted is:

[0014]

[0015] Hydraulic pad pre-acceleration: Before the upper die moves downward and contacts the blank holder, the hydraulic pad drives the blank holder downward in advance. At this time, the pilot electromagnetic ball valve is energized, and the A port and B port of the support cartridge valve are connected in both directions. The three-way control valve works in the working position of A port to T port. The hydraulic oil from the main oil source enters the rod chamber of the hydraulic cylinder, and the piston rod of the hydraulic cylinder retreats. At this stage, the desired blank holder force of the hydraulic pad is achieved. Fc The theoretical calculation speed at the time is the reference calculation control instruction, including the pre-acceleration instruction ugh and synchronous leveling control instructions ul . ul Using formula 2, ugh The calculation formula is:

[0016]

[0017] kv Available through product catalog.

[0018] The control signal of the three-way control valve during hydraulic pad pre-acceleration is:

[0019]

[0020] Hydraulic pad stretching: When stretching the workpiece, the upper die presses the edge holding device downward, and the piston rod of the hydraulic cylinder is also forced to move downward. At this time, the pilot electromagnetic ball valve is energized, and the A port and B port of the supporting cartridge valve are connected in both directions. The three-way control valve works in the working position of port A to port T. The hydraulic oil from the main oil source is replenished into the rod chamber of the hydraulic cylinder, and the piston rod of the hydraulic cylinder retreats. During stretching, the hydraulic cylinder and the hydraulic pad are forced to move. At this stage, it is necessary to control the edge holding force and the hydraulic pad to be parallel at the same time. The control command is controlled by the pre-acceleration command. ugh , Synchronous leveling control instructions ul , Blank holding force control command uc It consists of three parts. ul Using formula 2, ugh Using formula 4, uc The calculation formula is:

[0021]

[0022] fPID Is to make the hydraulic pad pressure force error he / she The PID control function should be as small as possible. Dad × Ah - Pb × Ab ) represents the resultant force of four groups of hydraulic cylinders.

[0023] The control signal of the three-way control valve when the hydraulic pad is stretched is:

[0024]

[0025] Hydraulic pad retraction: When the hydraulic pad needs to move downward actively, the pilot solenoid ball valve is energized, and the A port and B port of the support cartridge valve are bidirectionally connected. The three-way control valve works in the working position of port A to port T, and the hydraulic oil from the main oil source enters the rod chamber of the hydraulic cylinder, and the hydraulic cylinder piston rod retracts. The control method at this stage is the same as when the hydraulic pad is lifted, and the control signal of the three-way control valve is the same as formula 3.

[0026] Hydraulic pad suspension: When the hydraulic pad stops moving, the pilot solenoid ball valve is de-energized, the first shuttle valve and the second shuttle valve ensure that the highest system pressure acts on the control chamber of the support cartridge valve, the support cartridge valve is in a reliable cut-off state, the three-way control valve works in the working position of port A to port T, the rodless chamber of the hydraulic cylinder is cut off, and the piston rod of the hydraulic cylinder is stationary.

[0027] The beneficial effects of the present invention are as follows:

[0028] 1. The pre-acceleration control of the present invention can effectively alleviate the impact generated when the upper die contacts the edge holder, reduce the edge holder force fluctuation in the initial stage of stretching, and improve the stretching quality of the workpiece.

[0029] 2. The present invention realizes the coordinated control of the pressure force and movement of the hydraulic pad. The pressure force can be automatically and accurately adjusted as desired, and can adapt to more complex stretching and forming processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the principle of the hydraulic pad electro-hydraulic system of the present invention.

[0031] Figure 2 Flow chart of the control method of the present invention.

[0032] Figure 1 In: 1-three-way control valve, 2-first shuttle valve, 3-support cartridge valve, 4-pilot solenoid ball valve, 5-first safety valve, 6-second shuttle valve, 7-second safety valve, 8-hydraulic pad displacement sensor, 9-first pressure sensor, 10-hydraulic cylinder, 11-cylinder displacement sensor, 12-accumulator, 13-second pressure sensor, 14-controller, 301-hydraulic pad, 302-main oil source, 303-pilot control oil source. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings.

[0034] See also Figure 1The present invention mainly includes: the servo hydraulic pad electro-hydraulic system mainly includes a three-way control valve 1, a first shuttle valve 2, a support cartridge valve 3, a pilot electromagnetic ball valve 4, a first safety valve 5, a second shuttle valve 6, a second safety valve 7, a hydraulic pad displacement sensor 8, a first pressure sensor 9, a hydraulic cylinder 10, a cylinder displacement sensor 11, an accumulator 12, a second pressure sensor 13, and a controller 14; wherein the three-way control valve 1, the first shuttle valve 2, the support cartridge valve 3, the pilot electromagnetic ball valve 4, the first safety valve 5, the second shuttle valve 6, the second safety valve 7, the first pressure sensor 9, the hydraulic cylinder 10, the cylinder displacement sensor 1 1, the accumulator 12, and the second pressure sensor 13 form a group of electro-hydraulic drive shafts. The hydraulic cushion 301 is driven by four groups of electro-hydraulic drive shafts. The hydraulic cylinders 10 of the four groups of electro-hydraulic drive shafts are respectively installed at the four corners of the hydraulic cushion 301; the P port of the three-way control valve 1 is connected with the A port of the first shuttle valve 2, the oil inlet of the second safety valve 7, the rod chamber of the hydraulic cylinder 10, the oil port of the accumulator 12, the detection port of the second pressure sensor 13, and the main oil source 302; the A port of the three-way control valve 1 is connected with the A port of the support cartridge valve 3, and the B port of the support cartridge valve 3 is connected with the oil inlet of the first safety valve 5, the A port of the second shuttle valve 6, the first pressure The detection port of the force sensor 9 is connected to the rodless chamber of the hydraulic cylinder 10, the B port of the first shuttle valve 2 is connected to the control oil X port of the three-way control valve 1 and the pilot control oil source 303, the C port of the first shuttle valve 2 is connected to the B port of the second shuttle valve 6, the C port of the second shuttle valve 6 is connected to the P port of the pilot electromagnetic ball valve 4, the A port of the pilot electromagnetic ball valve 4 is connected to the control chamber of the support cartridge valve 3, the hydraulic oil tank is connected to the T port and the control oil Y port of the three-way control valve 1, the T port of the pilot electromagnetic ball valve 4, the oil outlet of the first safety valve 5, and the oil outlet of the second safety valve 7; the detection end of the hydraulic pad displacement sensor 8 is installed on the hydraulic pad 301, The detection end of the cylinder displacement sensor 11 is built into the hydraulic cylinder 10, and the controller 14 is electrically connected with the three-way control valve 1 amplifier, the pilot electromagnetic ball valve 4 electromagnet, the hydraulic pad displacement sensor 8 circuit, the first pressure sensor 9 circuit, the cylinder displacement sensor 11 circuit, and the second pressure sensor 13 circuit; the first shuttle valve 2 and the second shuttle valve 6 connect the pilot control oil source 303, the main oil source 302 and the rodless chamber of the hydraulic cylinder 10 with the highest pressure to the P port of the pilot electromagnetic ball valve 4. When the pilot electromagnetic ball valve 4 loses power, the support cartridge valve 3 is effectively cut off; the hydraulic pad displacement sensor 8 detects the displacement of the hydraulic pad 301 sc , and converts it into an electrical signal and transmits it to the controller 14, which can calculate the speed of the hydraulic pad 301 v.c. The first pressure sensor 9 detects the rodless chamber pressure of the hydraulic cylinder 10 Dad , and converted into an electrical signal and transmitted to the controller 14; the cylinder displacement sensor 11 detects the displacement of the hydraulic cylinder 10 in , and converts it into an electrical signal and transmits it to the controller 14, which can calculate the speed of the hydraulic cylinder 10 wowThe second pressure sensor 13 detects the rod chamber pressure of the hydraulic cylinder 10 Pb , and convert it into an electrical signal and transmit it to the controller 14; the controller 14 receives the sensor signal, executes the control algorithm, and converts the control command into an electrical signal to control the hydraulic valve; the flow coefficient of the three-way control valve 1 is kv ; The rodless chamber effective area of ​​the hydraulic cylinder 10 is Ah , the effective area of ​​the rod cavity is Ab .

[0035] See attached Figure 1 , 2 , a control method for a servo hydraulic pad electro-hydraulic system, characterized in that it comprises at least the following steps:

[0036] a) Hydraulic pad lifting: After the last stretching is completed, the hydraulic pad 301 needs to be lifted to the initial setting position. In this process, the pilot electromagnetic ball valve 4 is energized, and the A port and the B port of the support cartridge valve 3 are connected in both directions. The three-way control valve 1 works in the working position of the P port connecting the A port, and the hydraulic oil from the main oil source 302 enters the rodless cavity of the hydraulic cylinder 10, and the piston rod of the hydraulic cylinder 10 extends. The hydraulic circuit recycles the hydraulic oil flowing out of the rod cavity of the hydraulic cylinder 10, thereby reducing the rated input flow of the system, reducing the installed power, and saving energy; the controller 14 controls the displacement of the hydraulic pad 301 sc ,speed v.c. and the displacement of the hydraulic cylinder 10 in ,speed wow Calculate control instructions, control the three-way control valve 1 to adjust the speed of the hydraulic cylinder 10 and the hydraulic pad 301 and make the final positioning; the control instructions include motion control instructions oh and synchronous leveling control instructions ul Assume that the desired trajectory of the hydraulic pad 301 is scd ,but oh for:

[0037]

[0038] mPID Is to let the motion error escape , evc The smallest possible PID control function. oh The hydraulic pad 301 is moved along a desired trajectory.

[0039] ul The calculation formula is:

[0040]

[0041] θ x , θ yThey are the inclination angles of the hydraulic pad 301 in the front-to-back and left-to-right directions respectively. lPID Yes θ x , θ y The smallest possible PID control function. ul Make four groups of hydraulic axes move synchronously.

[0042] The control signal of the three-way control valve 1 when the hydraulic cushion 301 is lifted is:

[0043]

[0044] b) Hydraulic pad pre-acceleration: Before the upper die moves downward and contacts the blank holder, the hydraulic pad 301 drives the blank holder downward in advance. At this time, the pilot electromagnetic ball valve 4 is energized, and the A port and the B port of the support cartridge valve 3 are bidirectionally connected. The three-way control valve 1 works in the working position of the A port to the T port. The hydraulic oil from the main oil source 302 enters the rod chamber of the hydraulic cylinder 10, and the piston rod of the hydraulic cylinder 10 retreats. At this stage, the desired blank holder force of the hydraulic pad is achieved. Fc The theoretical calculation speed at the time is the reference calculation control instruction, including the pre-acceleration instruction ugh and synchronous leveling control instructions ul . ul Using formula 2, ugh The calculation formula is:

[0045]

[0046] kv Available through product catalog.

[0047] The control signal of the three-way control valve 1 during pre-acceleration of the hydraulic cushion 301 is:

[0048]

[0049] c) Hydraulic pad stretching: When stretching the workpiece, the upper die presses the edge holding device downward, and the piston rod of the hydraulic cylinder 10 is also forced to move downward. At this time, the pilot electromagnetic ball valve 4 is energized, and the A port and the B port of the supporting cartridge valve 3 are connected in both directions. The three-way control valve 1 works in the working position of the A port to the T port. The hydraulic oil from the main oil source 302 is replenished into the rod chamber of the hydraulic cylinder 10, and the piston rod of the hydraulic cylinder 10 retreats; during stretching, the hydraulic cylinder 10 and the hydraulic pad 301 are forced to move. At this stage, it is necessary to control the edge holding force to be parallel to the hydraulic pad 301 at the same time. The control command is controlled by the pre-acceleration command ugh , Synchronous leveling control instructions ul , Blank holding force control command uc It consists of three parts. ul Using formula 2, ugh Using formula 4, uc The calculation formula is:

[0050]

[0051] fPID Is to make the hydraulic pad pressure force error he / she The PID control function should be as small as possible. Dad × Ah - Pb × Ab ) represents the resultant force of four groups of hydraulic cylinders 10.

[0052] When the hydraulic cushion 301 is stretched, the control signal of the three-way control valve 1 is:

[0053]

[0054] d) Hydraulic pad retraction: When the hydraulic pad 301 needs to move downward actively, the pilot electromagnetic ball valve 4 is energized, and the A port and the B port of the supporting cartridge valve 3 are bidirectionally connected. The three-way control valve 1 works in the working position of the A port connecting to the T port. The hydraulic oil from the main oil source 302 enters the rod chamber of the hydraulic cylinder 10, and the piston rod of the hydraulic cylinder 10 retreats. The control method at this stage is the same as that when the hydraulic pad 301 is lifted, and the control signal of the three-way control valve 1 is the same as that of the formula 3.

[0055] e) Hydraulic pad suspension: When the hydraulic pad 301 stops moving, the pilot electromagnetic ball valve 4 is de-energized, the first shuttle valve 2 and the second shuttle valve 6 ensure that the highest system pressure acts on the control chamber of the support cartridge valve 3, the support cartridge valve 3 is in a reliable cut-off state, the three-way control valve 1 works in the working position of port A to port T, the rodless chamber of the hydraulic cylinder 10 is cut off, and the piston rod of the hydraulic cylinder 10 is stationary.

Claims

1. A servo hydraulic pad electro-hydraulic system, characterized in that: servo The hydraulic cushion electro-hydraulic system mainly includes a three-way control valve (1), a first shuttle valve (2), a support cartridge valve (3), a pilot electromagnetic ball valve (4), a first safety valve (5), a second shuttle valve (6), a second safety valve (7), a hydraulic cushion displacement sensor (8), a first pressure sensor (9), a hydraulic cylinder (10), a cylinder displacement sensor (11), an accumulator (12), a second pressure sensor (13), and a controller (14); wherein, the three-way control valve (1), the first shuttle valve (2), the support cartridge valve (3), the pilot electromagnetic ball valve (4), the first safety valve (5), the second shuttle valve (6), the second safety valve (7), the first pressure sensor (9), the hydraulic cylinder (10), the cylinder displacement sensor (11), the accumulator (12), the second pressure sensor (13), and the controller (14). ), a cylinder displacement sensor (11), an accumulator (12), and a second pressure sensor (13) form a group of electro-hydraulic drive shafts. The hydraulic cushion is driven by four groups of electro-hydraulic drive shafts. The hydraulic cylinders (10) of the four groups of electro-hydraulic drive shafts are respectively installed at the four corners of the hydraulic cushion; the P port of the three-way control valve (1) is connected to the A port of the first shuttle valve (2), the oil inlet of the second safety valve (7), the rod chamber of the hydraulic cylinder (10), the oil port of the accumulator (12), the detection port of the second pressure sensor (13), and the main oil source; the A port of the three-way control valve (1) is connected to the A port of the support cartridge valve (3); the B port of the support cartridge valve (3) is connected to the oil inlet of the first safety valve (5) and the A port of the second shuttle valve (6). , the detection port of the first pressure sensor (9) is connected to the rodless chamber of the hydraulic cylinder (10); the B port of the first shuttle valve (2) is connected to the control oil X port of the three-way control valve (1) and the pilot control oil source; the C port of the first shuttle valve (2) is connected to the B port of the second shuttle valve (6); the C port of the second shuttle valve (6) is connected to the P port of the pilot electromagnetic ball valve (4); the A port of the pilot electromagnetic ball valve (4) is connected to the control chamber of the support cartridge valve (3); the hydraulic oil tank is connected to the T port and the control oil Y port of the three-way control valve (1), the T port of the pilot electromagnetic ball valve (4), the oil outlet of the first safety valve (5), and the oil outlet of the second safety valve (7); the detection end of the hydraulic pad displacement sensor (8) is installed on the liquid The pressure pad and the cylinder displacement sensor (11) detection end are built into the hydraulic cylinder (10); the controller (14) is electrically connected to the three-way control valve (1) amplifier, the pilot electromagnetic ball valve (4) electromagnet, the hydraulic pad displacement sensor (8) circuit, the first pressure sensor (9) circuit, the cylinder displacement sensor (11) circuit, and the second pressure sensor (13) circuit; the first shuttle valve (2) and the second shuttle valve (6) connect the pilot control oil source, the main oil source and the highest pressure in the rodless chamber of the hydraulic cylinder (10) to the P port of the pilot electromagnetic ball valve (4); when the pilot electromagnetic ball valve (4) loses power, the support cartridge valve (3) is effectively cut off; the hydraulic pad displacement sensor (8) detects the displacement of the hydraulic pad sc , and converts it into an electrical signal and transmits it to the controller (14). The controller (14) can calculate the speed of the hydraulic pad. vc ; The first pressure sensor (9) detects the rodless chamber pressure of the hydraulic cylinder (10) Pa , and converts it into an electrical signal and transmits it to the controller (14); the cylinder displacement sensor (11) detects the displacement of the hydraulic cylinder (10) s , and converts it into an electrical signal and transmits it to the controller (14). The controller (14) can calculate the speed of the hydraulic cylinder (10) va The second pressure sensor (13) detects the rod chamber pressure of the hydraulic cylinder (10) Pb , and converts it into an electrical signal and transmits it to the controller (14); the controller (14) receives the sensor signal, executes the control algorithm, and converts the control command into an electrical signal to control the hydraulic valve; the flow coefficient of the three-way control valve (1) is kv ; The effective area of ​​the rodless chamber of the hydraulic cylinder (10) is Aa , the effective area of ​​the rod cavity is Ab .

2. The control method of a servo hydraulic pad electro-hydraulic system according to claim 1, characterized in that: At least the following steps are included: Hydraulic pad lifting: After the last stretching is completed, the hydraulic pad needs to be lifted to the initial setting position. During this process, the pilot electromagnetic ball valve (4) is energized, and the A port and the B port of the support cartridge valve (3) are bidirectionally connected. The three-way control valve (1) works in the working position of the P port connecting the A port. The hydraulic oil from the main oil source enters the rodless chamber of the hydraulic cylinder (10), and the piston rod of the hydraulic cylinder (10) extends. The hydraulic circuit recycles the hydraulic oil flowing out of the rod chamber of the hydraulic cylinder (10), thereby reducing the rated input flow of the system, reducing the installed power, and saving energy. The controller (14) controls the displacement of the hydraulic pad. sc ,speed vc and the displacement of the hydraulic cylinder (10) s ,speed va Calculate control instructions, control the three-way control valve (1) to adjust the speed of the hydraulic cylinder (10) and the hydraulic pad and make the final positioning; the control instructions include motion control instructions um and synchronous leveling control instructions ul ; Assume that the desired trajectory of the hydraulic pad is scd ,but um for mPID Is to let the motion error esc , evc The PID control function should be as small as possible; um Make the hydraulic pad move along the desired trajectory; ul The calculation formula is θ x , θ y They are the inclination angles of the hydraulic pad in the front-back and left-right directions respectively; PID Yes θ x , θ y The PID control function should be as small as possible; ul Make four sets of hydraulic axes move synchronously; The control signal of the three-way control valve (1) when the hydraulic cushion is lifted is: Hydraulic pad pre-acceleration: Before the upper die moves downward and contacts the blank holder, the hydraulic pad drives the blank holder downward in advance. At this time, the pilot electromagnetic ball valve (4) is energized, and the A and B ports of the support cartridge valve (3) are bidirectionally connected. The three-way control valve (1) works in the working position of A port to T port. The hydraulic oil from the main oil source enters the rod chamber of the hydraulic cylinder (10), and the piston rod of the hydraulic cylinder (10) retreats. At this stage, the desired blank holder force of the hydraulic pad is achieved. Fc The theoretical calculation speed at the time is the reference calculation control instruction, including the pre-acceleration instruction u and synchronous leveling control instructions ul ; ul Using formula 2, u The calculation formula is kv It can be obtained through product samples; The control signal of the three-way control valve (1) during the pre-acceleration of the hydraulic cushion is Hydraulic pad stretching: When stretching the workpiece, the upper die presses the blank holder downward, and the piston rod of the hydraulic cylinder (10) is also forced to move downward. At this time, the pilot electromagnetic ball valve (4) is energized, and the A port and the B port of the support cartridge valve (3) are bidirectionally connected. The three-way control valve (1) works in the working position of the A port connecting to the T port. The hydraulic oil from the main oil source is replenished into the rod chamber of the hydraulic cylinder (10), and the piston rod of the hydraulic cylinder (10) is retracted. During stretching, the hydraulic cylinder (10) and the hydraulic pad are forced to move. At this stage, it is necessary to simultaneously control the blank holder force and the hydraulic pad to be parallel. The control command is the pre-acceleration command. u , Synchronous leveling control instructions ul , Blank holding force control command uc It consists of three parts; ul Calculated using formula 2, u Calculated using formula 4, uc The calculation formula is fPID Is to make the hydraulic pad pressure force error ef As small a PID control function as possible;∑( Pa × Aa - Pb × Ab ) represents the resultant force of the four groups of hydraulic cylinders (10); When the hydraulic cushion is stretched, the control signal of the three-way control valve (1) is Hydraulic cushion retraction: When the hydraulic cushion needs to be actively moved downward, the pilot solenoid ball valve (4) is energized, and the A port and the B port of the support cartridge valve (3) are bidirectionally connected. The three-way control valve (1) works in the working position of the A port connecting to the T port. The hydraulic oil from the main oil source enters the rod chamber of the hydraulic cylinder (10), and the piston rod of the hydraulic cylinder (10) retracts. The control method at this stage is the same as that when the hydraulic cushion is lifted. The control signal of the three-way control valve (1) is the same as that of Formula 3. Hydraulic cushion suspension: When the hydraulic cushion stops moving, the pilot electromagnetic ball valve (4) is de-energized, the first shuttle valve (2) and the second shuttle valve (6) ensure that the highest system pressure acts on the control chamber of the support cartridge valve (3), the support cartridge valve (3) is in a reliable cut-off state, the three-way control valve (1) works in the working position of port A to port T, the rodless chamber of the hydraulic cylinder (10) is cut off, and the piston rod of the hydraulic cylinder (10) is stationary.

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