A kind of pipe expansion axial feed force and internal pressure decoupling coordinated control system

Abstract

The present application relates to the technical fields of metal tube hydraulic forming, and discloses a kind of pipe expansion axial feed force and the decoupling coordination control system of internal pressure, comprising: forming host unit, including the forming die with forming cavity and the axial feed mechanism configured to move along the axis direction of tube blank, the axial feed mechanism has the movement component of generating axial feed displacement;Hydraulic power unit is configured to inject liquid medium into the internal cavity of the tube blank and establish forming pressure;Central control unit is configured to send control instructions to the axial feed mechanism and the hydraulic power unit;Variable transmission ratio volume modulation unit is arranged between the axial feed mechanism and the internal fluid circuit of the tube blank.The present application rigidly couples axial feed motion and volume compensation action at physical level through nonlinear mechanical linkage mechanism, and realizes the essential decoupling of feed motion and internal pressure fluctuation.

Description

Technical Field

[0001] This invention relates to the field of hydraulic forming technology for metal pipes, specifically a decoupled and coordinated control system for the axial feed force and internal pressure of pipe expansion forming. Background Technology

[0002] In the tube forming process, the coordinated control of axial feeding and internal high-pressure fluid is a key factor determining the forming quality. As the geometric complexity of tubes increases, the forming process places higher demands on the real-time matching of feeding accuracy and pressure stability.

[0003] Current tube forming equipment typically employs independent axial feed control loops and hydraulic control loops. During the initial forming stage and the feeding process, the intrusion of the axial pusher directly reduces the volume of the enclosed space inside the tube blank. Due to the compressibility of the liquid medium, this rapid change in volume causes drastic pressure fluctuations within the tube blank. Existing control methods primarily rely on feedback signals from pressure sensors to adjust the output flow of the hydraulic pump station or booster to counteract the effects of volume changes. However, there is an inherent time lag between the hydraulic components receiving the signal and the actuator's action. This delay in dynamic response prevents the system from eliminating the interference of the feed motion on the internal pressure in real time, resulting in significant oscillations and lag in pressure control.

[0004] After entering the tube blank plastic forming stage, the rapid expansion of the tube diameter generates a large instantaneous volume increase demand. At this time, the hydraulic system needs to replenish the tube blank cavity with high-pressure fluid. Traditional feeding methods rely entirely on the hydraulic power source to provide the entire flow required for forming. This not only requires the pump source to have extremely high output power and extremely fast response speed, but also makes it prone to pressure overshoot during high-flow feeding. Since the displaced flow generated by axial feed cannot be directly converted into an effective feeding source, the system consumes a large amount of external energy while struggling to ensure precise adjustment of the wall thickness distribution within the complex deformation range, easily leading to defects such as tube cracking or instability and wrinkling.

[0005] Furthermore, existing control systems often employ a single pressure closed-loop control logic, with the controller's load entirely focused on compensating for errors in measured pressure. In this mode, the system lacks an effective mechanical feedforward mechanism to pre-balance volume evolution. Because the hydraulic control loop and mechanical feed loop lack physical rigid constraints, the system struggles to accurately locate the fault source through a single signal comparison in the event of hydraulic leakage or mechanical jamming. This control logic, lacking redundant monitoring mechanisms, makes the system prone to inaccurate control precision and even logical inconsistencies when dealing with sudden changes in process parameters or mechanical wear, thus reducing the safety and reliability of the forming process. Summary of the Invention

[0006] To achieve the above objectives, the present invention provides the following technical solution: a decoupled and coordinated control system for the axial feed force and internal pressure of a pipe fitting during bulging, comprising: The forming main unit includes a forming mold with a forming cavity and an axial feed mechanism configured to move along the axis of the tube blank, the axial feed mechanism having a moving component that generates axial feed displacement; A hydraulic power unit is configured to inject a liquid medium into the internal cavity of the tube blank and establish forming pressure; The central control unit is configured to send control commands to the axial feed mechanism and the hydraulic power unit; A variable transmission ratio volume modulation unit is disposed between the axial feed mechanism and the internal fluid circuit of the tube blank; The variable transmission ratio volume modulation unit includes a volume compensation cylinder and a nonlinear mechanical linkage mechanism; The central control unit further integrates a constraint reference model module and an intelligent decoupling algorithm module, specifically: The constraint reference model module is configured to store and dynamically generate multi-dimensional safety constraint boundaries for the tube blank forming process; the constraint reference model is constructed based on the forming limit diagram (FLD) of the tube blank material, and maps the axial feed and internal pressure during the forming process into a safety allowable domain, a wrinkling risk domain, and a rupture risk domain; The intelligent decoupling algorithm module is configured to calculate the residual coupling amount after mechanical decoupling based on the data from the sensor feedback network, and generate dynamic compensation commands for the hydraulic power unit.

[0007] The volume compensation cylinder has a hydraulic working chamber in fluid communication with the internal cavity of the tube blank, and has a movable component capable of changing the volume of the hydraulic working chamber. The nonlinear mechanical linkage mechanism physically connects the moving part of the axial feed mechanism with the movable part of the volume compensation cylinder; The nonlinear mechanical linkage mechanism is configured to establish a rigid position mapping relationship between the axial feed displacement of the axial feed mechanism and the volume adjustment movement of the volume compensation cylinder, so that when the axial feed mechanism feeds into the tube blank, it synchronously drives the volume compensation cylinder to change the volume of the hydraulic working chamber to absorb or discharge fluid.

[0008] Preferably, the volume compensation cylinder includes a cylinder body assembly and a compensation piston assembly coaxially slidably disposed therein; The compensation piston assembly divides the internal space of the cylinder assembly into a variable-capacity working chamber and a back pressure balance chamber. The variable-capacity working chamber is connected in parallel with the internal cavity of the tube blank through a high-pressure flow guide pipe, so that the variable-capacity working chamber, the high-pressure flow guide pipe and the internal cavity of the tube blank together constitute a closed fluid control body; The compensation piston assembly includes a drive piston rod extending to the outside of the cylinder assembly, the drive piston rod being rigidly connected to the nonlinear mechanical linkage mechanism.

[0009] Preferably, the back pressure balancing chamber is provided with a fluid interface leading to the low-pressure side or the atmospheric environment; The hydraulic power unit is connected to the closed fluid control body via a main inlet pipeline, and the hydraulic power unit is configured to supplement the pressure of the closed fluid control body to establish the required flow difference according to the instructions of the central control unit.

[0010] Preferably, the nonlinear mechanical linkage mechanism adopts a cam drive architecture, including: A variable curvature cam plate is rigidly fixed to the moving part of the axial feed mechanism and has a shaped guide surface. The driven roller assembly is rotatably connected to the end of the drive piston rod and abuts against the forming guide surface; A reset biasing assembly is configured to apply a biasing force to the compensating piston assembly to maintain continuous contact between the driven roller assembly and the forming guide surface.

[0011] Preferably, the nonlinear mechanical linkage mechanism adopts a linkage transmission structure, including: An adjustable fulcrum assembly is fixedly mounted on the frame of the forming main unit; The swing lever assembly is rotatably mounted on the adjustable fulcrum seat assembly via a central pivot. The input linkage assembly is hinged at both ends to the moving part of the axial feed mechanism and one end of the swing lever assembly, respectively. The output linkage assembly is hinged at both ends to the other end of the swing lever assembly and the drive piston rod, respectively. The adjustable fulcrum assembly is configured to adjust the position of the central pivot on the swing lever assembly to change the length ratio of the input lever arm to the output lever arm.

[0012] Preferably, the forming guide surface has a linear holding section and a nonlinear modulation section distributed along the axial direction; The forming process of the tube blank is defined by an elastic deformation range and a plastic forming range; the linear holding section has a constant profile slope and is configured to make the absorption flow rate generated by the volume compensation cylinder due to the retraction movement equal to the discharge flow rate generated by the axial feed mechanism due to the feed movement when the tube blank is in the elastic deformation range, thereby maintaining the net flow rate of the fluid control body at zero. The nonlinear modulation segment has a varying profile slope and is configured such that when the tube blank is in the plastic forming range, the absorption flow rate generated by the volume compensation cylinder is less than the discharge flow rate generated by the axial feed mechanism, thereby generating a positive net mechanical flow rate inside the fluid control body.

[0013] Preferably, the instantaneous geometric transmission ratio of the nonlinear mechanical linkage mechanism is determined based on the ratio of the effective cross-sectional area of ​​the pusher of the axial feed mechanism to the effective cross-sectional area of ​​the compensating piston of the volume compensation cylinder; Furthermore, when the tube blank is in the plastic forming range, the instantaneous geometric transmission ratio is also configured to be related to the rate of change of the tube blank's internal volume with respect to the feed displacement, so that the net mechanical flow generated by the nonlinear mechanical linkage mechanism matches the volume growth rate of the tube blank due to plastic deformation.

[0014] Preferably, it further includes a sensing feedback network, the sensing feedback network comprising: A displacement detection sensor is configured to measure the axial feed displacement of the axial feed mechanism in real time; A pressure sensor is configured to measure the hydrostatic pressure of the fluid in the internal fluid circuit of the tube blank in real time; A piston position monitoring sensor is configured to measure the actual retraction displacement of the compensation piston in the volume compensation cylinder in real time.

[0015] Preferably, the central control unit is configured to store the theoretical position mapping function of the nonlinear mechanical linkage mechanism; The central control unit compares the axial feed displacement collected by the displacement detection sensor with the actual retraction displacement collected by the piston position monitoring sensor in real time. If the correspondence between the two deviates from the theoretical position mapping function by more than a preset tolerance, the nonlinear mechanical linkage mechanism is determined to have malfunctioned and a shutdown protection is triggered.

[0016] Preferably, the intelligent decoupling algorithm module adopts a feedforward-feedback composite control logic based on a disturbance observer, specifically configured as follows: A nominal system model incorporating mechanical linkage characteristics is established, defining the pressure and flow deviations caused by billet wall thickness tolerance, material hardening fluctuations, and mechanical wear during the actual forming process as generalized disturbances; the intelligent decoupling algorithm module calculates the generalized disturbances in real time and superimposes an anti-phase compensation component into the active flow command of the hydraulic power unit, thereby achieving soft decoupling of microfluidic dynamics based on mechanical hard decoupling.

[0017] Preferably, a decoupled and coordinated control method for the axial feed force and internal pressure of a pipe fitting bulging process includes the following steps: Step S100: Based on the volume evolution law of the tube blank to be processed, plan the mechanical transmission ratio distribution of the nonlinear mechanical linkage mechanism, configure the geometric parameters of the nonlinear mechanical linkage mechanism accordingly, initialize the constraint reference model, import the constitutive equation of the tube blank material into the central control unit, and generate the feed displacement. Changing dynamic pressure upper limit (Fragmentation prevention boundary) and lower limit of dynamic pressure (Anti-wrinkling boundary); Step S200: Load the tube blank into the forming mold and inject a liquid medium into the tube blank to establish a closed fluid control body; Step S300: Control the axial feed mechanism to perform axial feed, and simultaneously drive the volume compensation cylinder to retract linearly through the nonlinear mechanical linkage mechanism, so that the flow rate absorbed by the volume compensation cylinder offsets the flow rate displaced by the axial feed mechanism, maintaining the net flow rate of the closed fluid control body at zero. The intelligent decoupling algorithm monitors the hydrostatic pressure of the fluid in real time. volatility ,like If the preset threshold is exceeded, the algorithm determines that it is a mechanical linkage lag or a seal compressibility error, and immediately controls the hydraulic power unit to output high-frequency micro-flow pulses for dynamic correction. Step S400: When the axial feed mechanism enters the plastic forming zone, the nonlinear mechanical linkage mechanism drives the volume compensation cylinder to retract in a nonlinear proportion, generating a positive net mechanical flow to fill the new volume generated by the plastic deformation of the tube blank. The intelligent decoupling algorithm performs the following operations: Real-time display of current working point Mapped to the constraint reference model; Calculate the forming trajectory and Approximation index; When the approximation index exceeds the safety warning value, the algorithm temporarily takes over the control, prioritizes adjusting the output pressure of the hydraulic power unit, and performs secondary flow shaping on the net mechanical flow generated by the nonlinear mechanical linkage mechanism to ensure that the forming path is always within the safe allowable range. Step S500: Control the axial feed mechanism to stop moving, and control the hydraulic power unit to increase the pressure to shape the tube blank.

[0018] This invention provides a decoupled and coordinated control system for the axial feed force and internal pressure of pipe fittings during bulging. It offers the following advantages: (1) This invention firstly uses a nonlinear mechanical linkage mechanism to rigidly couple the axial feed motion and the volume compensation action at the physical level, thereby eliminating the main interference of the feed action on the internal pressure from the physical source and solving the problem of response lag in traditional hydraulic forming. On this basis, an intelligent decoupling algorithm is used to calculate and compensate for fluid compressibility drift, seal friction fluctuation and mechanical micro-wear that cannot be completely eliminated by mechanical linkage in real time, ensuring that the system maintains extremely high pressure control accuracy during long-term operation and high-speed forming.

[0019] (2) This invention introduces a constraint reference model based on the forming limit diagram (FLD). The system can map the working condition to the safety domain composed of wrinkling and cracking boundaries in real time. When the forming trajectory approaches the dangerous edge, the algorithm actively adjusts the hydraulic power unit to perform secondary shaping on the net mechanical flow, so that the system has the ability to adapt when facing differences in pipe batches or uneven material, effectively avoiding cracking and unstable wrinkling.

[0020] (3) The present invention adopts a parallel architecture of volume feedforward (mechanical first channel) and pressure feedback (hydraulic second channel). Combined with disturbance observer technology, the first channel is responsible for high flow compensation without hysteresis, and the second channel is responsible for online estimation and cancellation of unmodeled disturbances. With dual redundant monitoring of displacement and piston position, the central control unit can compare the deviation between the actual motion law and the preset mapping function in real time, thereby ensuring forming accuracy while having the ability to make immediate judgment and protection against mechanical faults. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the system framework of the present invention; Figure 2 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Please see Figure 1 This invention provides a decoupled and coordinated control system for the axial feed force and internal pressure of pipe expansion forming, which mainly includes: a forming host unit, a hydraulic power unit, a variable transmission ratio volume modulation unit, and a central control unit.

[0024] The main unit, as the basic support platform of the system, includes a forming mold and an axial feed mechanism. The forming mold has a cavity corresponding to the shape of the target part. The axial feed mechanism includes a drive source and a pusher at the end. The pusher is configured to move along the axial direction of the tube blank, abut against the end of the tube blank and form a seal, thereby applying an axial load to the tube blank and generating an axial feed displacement.

[0025] The hydraulic power unit is connected to the internal cavity of the tube blank through a high-pressure pipeline. It is responsible for injecting liquid medium into the tube blank and establishing the hydrostatic pressure required for forming. The hydraulic power unit includes an independent high-pressure booster source, which is configured to provide the tube blank with time-varying forming pressure and supplemental flow required for plastic deformation.

[0026] The variable transmission ratio volume modulation unit is located between the axial feed mechanism and the internal fluid circuit of the tube blank. As a passive adjustment device for fluid-structure interaction, the variable transmission ratio volume modulation unit includes a volume compensation cylinder and a nonlinear mechanical linkage mechanism.

[0027] The volume compensation cylinder has an independent hydraulic working chamber, which forms a parallel branch with the internal cavity of the tube blank through a fluid circuit. The volume compensation cylinder is equipped with a movable compensation piston, which changes the effective volume of the hydraulic working chamber connected to the system through the reciprocating motion of the compensation piston.

[0028] The nonlinear mechanical linkage mechanism physically connects the moving parts of the axial feed mechanism with the compensation piston of the volume compensation cylinder. It is used to convert the axial feed displacement generated by the axial feed mechanism into the linear displacement of the compensation piston of the volume compensation cylinder according to a preset mapping relationship. The nonlinear mechanical linkage mechanism has a variable mechanical transmission ratio, which is determined by the cam profile or connecting rod geometry parameters inside the mechanism.

[0029] The central control unit is connected to the axial feed mechanism and the hydraulic power unit via signal lines. It is used to send displacement commands to the axial feed mechanism and pressure commands to the hydraulic power unit according to the preset process curve.

[0030] During system operation, the axial feed mechanism passively drives the volume compensation cylinder through a nonlinear mechanical linkage mechanism. The volume compensation cylinder absorbs or expels fluid in real time according to the transmission relationship defined by the nonlinear mechanical linkage mechanism, thereby mechanically modulating the total volume change rate of the fluid circuit inside the tube blank. The hydraulic power unit independently replenishes the remaining volume and pressure required for the plastic deformation of the tube blank to maintain the required flow rate.

[0031] The volumetric compensation cylinder mainly includes a cylinder body assembly, a compensation piston assembly, and a high-pressure guide pipeline. The volumetric compensation cylinder is a single-rod linear hydraulic actuator, and its pressure resistance rating is matched with the maximum internal pressure required for pipe forming.

[0032] The cylinder assembly is rigidly fixed to the base of the forming host unit by bolts or flanges. The cylinder assembly has a cylindrical inner hole, a closed cylinder bottom at one end, and an end cap with a central through hole at the other end.

[0033] The compensating piston assembly is coaxially and slidably disposed in the inner hole of the cylinder assembly. The compensating piston assembly includes a compensating piston body and a drive piston rod connected to one side of the compensating piston body. The outer peripheral surface of the compensating piston body is in contact with the inner hole wall of the cylinder assembly.

[0034] The compensating piston body divides the internal space of the cylinder assembly into two independent chambers: a variable displacement working chamber and a back pressure balance chamber. In this embodiment, the variable displacement working chamber is located on the side of the compensating piston body away from the driving piston rod (i.e., the rodless chamber), and the back pressure balance chamber is located on the side of the compensating piston body closer to the driving piston rod (i.e., the rod chamber). The driving piston rod passes through the back pressure balance chamber and extends to the outside of the cylinder assembly through the central through hole of the end cap.

[0035] A first fluid interface is provided on the bottom or side wall of the variable volume working chamber. One end of the high pressure guide pipe is connected to the first fluid interface, and the other end is directly connected to the internal cavity of the tube blank or the main liquid inlet circuit of the forming host unit. Through the high pressure guide pipe, the variable volume working chamber and the internal cavity of the tube blank form a parallel fluid passage, so that the fluid pressure in the variable volume working chamber and the fluid pressure in the tube blank are balanced in real time.

[0036] The end of the drive piston rod extending outside the cylinder assembly is provided with a mechanical coupling interface. This mechanical coupling interface is an external thread structure, a flange structure, or a pin-connected lug structure. The mechanical coupling interface is used to establish a rigid connection with the nonlinear mechanical linkage mechanism. Under the drive of the nonlinear mechanical linkage mechanism, the drive piston rod drives the compensation piston body to reciprocate axially within the cylinder assembly, thereby changing the volume of the variable displacement working chamber.

[0037] The compensating piston assembly also includes a combined sealing ring disposed on the circumference of the compensating piston body to isolate the variable displacement working chamber from the back pressure balance chamber. The cylinder assembly is provided with a guide sleeve and a rod sealing assembly at the end cap through which the driving piston rod passes, for radial support and axial dynamic sealing of the driving piston rod.

[0038] The back pressure balance chamber is equipped with a second fluid interface, which is connected to a low-pressure oil tank or atmospheric environment to maintain a constant pressure in the back pressure balance chamber and eliminate back pressure resistance during piston movement.

[0039] The nonlinear mechanical linkage mechanism adopts a flat cam direct-acting push rod transmission architecture. The nonlinear mechanical linkage mechanism includes a variable curvature cam plate, a driven roller assembly, a linear guide seat, and a reset bias assembly.

[0040] The variable curvature cam plate is horizontally set and rigidly fixed to the moving parts of the axial feed mechanism by bolt assembly. The length direction of the variable curvature cam plate is parallel to the axis direction of the tube blank and moves axially linearly synchronously with the axial feed mechanism.

[0041] The upper or side surface of the variable curvature cam plate is machined with a forming guide surface. The forming guide surface has a lift coordinate that changes continuously along the axial direction. Its profile curve includes a linear holding segment and a nonlinear modulation segment. The profile slope of the linear holding segment is constant, and the profile slope of the nonlinear modulation segment is variable.

[0042] In this embodiment, the axis of the volume compensation cylinder is arranged perpendicular to the motion axis of the axial feed mechanism. The driven roller assembly is rotatably connected to the end of the drive piston rod of the volume compensation cylinder, and the outer circumferential surface of the driven roller assembly abuts against the forming guide surface of the variable curvature cam plate.

[0043] The linear guide seat is fixedly mounted on the frame of the forming main unit, located between the variable curvature cam plate and the volume compensation cylinder. The driving piston rod passes through the guide hole of the linear guide seat. The linear guide seat is used to constrain the driving piston rod to only produce linear motion perpendicular to the axial feed direction, and to bear the lateral component force from the variable curvature cam plate.

[0044] The reset bias assembly is sleeved outside the drive piston rod, between the linear guide seat and the mechanical coupling interface. The reset bias assembly is a high-stiffness helical compression spring, and its elastic force is directed towards the variable curvature cam plate, maintaining continuous contact between the driven roller assembly and the forming guide surface.

[0045] Furthermore, the nonlinear mechanical linkage mechanism can also adopt an adjustable fulcrum swing linkage architecture, which includes an input linkage assembly, a swing lever assembly, an adjustable fulcrum seat assembly, and an output linkage assembly.

[0046] One end of the input linkage assembly is hinged to the moving part of the axial feed mechanism via a first rotating pin, and the other end is hinged to one end of the swing lever assembly via a second rotating pin. The input linkage assembly is used to convert the linear motion of the axial feed mechanism into the driving torque of the swing lever assembly.

[0047] The swing lever assembly is a rigid long rod, and the adjustable fulcrum seat assembly is fixedly installed on the frame of the forming main unit, located between the axial feed mechanism and the volume compensation cylinder.

[0048] The swing lever assembly is rotatably mounted on the adjustable fulcrum seat assembly via a central pivot. The key point is that the central pivot is located between the hinge points at both ends of the swing lever assembly, so that the swing lever assembly forms a single-stage lever structure. The central pivot divides the swing lever assembly into an input lever arm segment and an output lever arm segment.

[0049] The adjustable fulcrum assembly is equipped with an adjustment groove and a position locking nut extending along the length of the swing lever assembly. By changing the fixed position of the central pivot on the swing lever assembly, the length ratio of the input lever segment to the output lever segment is continuously adjusted, thereby setting the basic volume compensation ratio of the system.

[0050] One end of the output linkage assembly is hinged to the other end of the swing lever assembly (i.e., the end away from the input linkage assembly) via a third rotating pin, and the other end is hinged to the mechanical coupling interface on the drive piston rod of the volume compensation cylinder via a fourth rotating pin.

[0051] During system operation, the axial feed mechanism feeds forward in a straight line. The input linkage assembly pushes the swing lever assembly to rotate around the central pivot. Due to the reverse action of the lever, the output end of the swing lever assembly pulls the output linkage assembly, which in turn drives the drive piston rod of the volume compensation cylinder to retract. This reverse linkage mechanism ensures that the volume compensation cylinder simultaneously frees up volume space when the pusher is inserted into the billet.

[0052] Meanwhile, as the axial feed increases, the transmission angle between the input connecting rod assembly and the swing lever assembly, as well as the transmission angle between the output connecting rod assembly and the drive piston rod, changes continuously. This evolution of geometric angles causes the instantaneous speed of the drive piston rod to exhibit nonlinear characteristics relative to the axial feed speed. This nonlinear characteristic is used to match the nonlinear volume growth requirements during the plastic deformation stage of the tube blank.

[0053] Furthermore, this invention utilizes a nonlinear mechanical linkage mechanism to establish a rigid motion constraint between the axial feed mechanism and the volumetric compensation cylinder. This constraint relationship follows the following kinematic mapping model, specifically: set up Let time be the variable, and define the axial feed displacement of the axial feed mechanism as... The direction in which the pusher moves toward the inside of the tube blank is defined as the positive direction; the corresponding feed rate is... .

[0054] The displacement of the compensating piston of the volumetric compensating cylinder is defined as... The direction in which the piston retracts outward, increasing the volume of the hydraulic chamber, is defined as the positive direction; the corresponding speed is... .

[0055] The geometric characteristics of nonlinear mechanical linkage mechanisms determine Position mapping function between For cam-type structures, For cam lift curves; for linkage structures, The analytical relationship between the mechanism and the two satisfy the position constraint equation: in: : Compensate for the displacement of the piston assembly; : Displacement of the axial feed mechanism; : The mechanical modulation function determined by the geometric characteristics of the mechanism.

[0056] Regarding time Differentiating, we obtain the velocity transfer equation: in: : Compensation for the instantaneous speed of the piston assembly; : Instantaneous speed of the axial feed mechanism; Mapping function For displacement The spatial derivative of .

[0057] Define instantaneous geometric transmission ratio : in: Depends only on the current feed position Instantaneous transmission ratio, Combining the above formulas, the response speed of the volumetric compensation cylinder can be expressed as: This model shows that by designing the geometric parameters of the mechanism, Distributed according to a preset pattern, the volumetric compensation speed can be achieved. Axial feed rate Passive following and adjustment.

[0058] Furthermore, the present invention defines the internal cavity of the tube blank, the variable volume working chamber of the volume compensation cylinder, and the high-pressure guide pipe connecting the two as a closed fluid control body. The fluid mass inside the fluid control body is conserved and follows the principle of fluid continuity. Based on this principle, the dynamic characteristics of the internal fluid pressure (i.e., the rate of pressure change) of the fluid control body are determined by the net flow rate of the system and satisfy the following flow balance equation.

[0059] The relevant physical quantity parameters are set as follows: : Instantaneous total volume of the fluid control volume; : Effective bulk modulus of elasticity of hydraulic medium; Hydrostatic pressure Regarding time The first derivative; : Active flow injected by the hydraulic power unit; Volume growth rate due to plastic deformation of tube blank ; : These are the effective cross-sectional areas of the axial feed pusher and the compensating piston, respectively.

[0060] According to the aforementioned principle of fluid continuity, the rate of change of pressure in the control volume depends on the algebraic sum of the input flow rate and the output flow rate: in, The axial feed rate as defined above. The compensated piston speed is as defined above.

[0061] Speed ​​transmission relationship Substituting into the above equation, we obtain the modified flow balance equation describing the dynamic pressure characteristics of the system: In the formula Defined as net mechanical flow item , When the system is in the linear holding phase, set ,but , eliminate from the equation This indicates that the pressure dynamics are no longer affected by the feed rate, thus achieving decoupling.

[0062] When the system is in the nonlinear modulation range, set ,but Compensating for deformable flow rate using net mechanical flow rate This reduces the load on the pump source.

[0063] Furthermore, the system also includes a sensor feedback network, which is connected to each execution component and the central control unit of the system, and is used to collect physical state parameters during system operation in real time and provide feedback signals.

[0064] The sensor feedback network includes a displacement detection sensor mounted on the axial feed mechanism. The displacement detection sensor can be a linear encoder, magnetostrictive displacement sensor, or rotary encoder, and is rigidly mounted between the stator and mover of the axial feed mechanism. The displacement detection sensor is used to measure the absolute axial displacement of the pusher of the axial feed mechanism relative to the mechanical origin in real time, denoted as . The symbol In accordance with the feed displacement defined in the aforementioned kinematic model, the central control unit will transmit this real-time displacement signal. The current forming stage of the tube blank (elastic deformation range or plastic forming range) is determined by comparing it with the preset process position threshold, thereby switching the control logic of the hydraulic power unit.

[0065] The sensor feedback network includes pressure sensors installed in the high-pressure guide pipeline, the variable-volume working chamber of the volume compensation cylinder, or the pressure measurement interface of the forming mold. The pressure sensors are piezoresistive or piezoelectric pressure transmitters, whose sensing probes directly contact the hydraulic medium inside the fluid control body to measure the static pressure of the fluid inside the system in real time, denoted as . The symbol In accordance with the fluid pressure defined in the aforementioned flow balance equation, during the shaping and pressure holding phases, the central control unit uses this pressure signal... The main booster pump of the hydraulic power unit is controlled by PID closed-loop as a feedback variable.

[0066] The sensor feedback network also includes a piston position monitoring sensor mounted on the volume compensation cylinder. This piston position monitoring sensor detects the actual retraction displacement of the compensation piston assembly, denoted as... The symbol Consistent with the output displacement defined in the aforementioned kinematic model, the piston position monitoring sensor and the displacement detection sensor constitute a dual redundant monitoring architecture.

[0067] Central control unit reads in real time and The values ​​are then used to verify whether the two satisfy the position mapping relationship defined in the aforementioned kinematic model: in: The real-time position of the compensated piston assembly, as measured by the piston position monitoring sensor; The real-time position of the axial feed mechanism as measured by the displacement detection sensor; The aforementioned definition of the mechanical modulation function of a nonlinear mechanical linkage mechanism characterizes the theoretical design... Follow Changing geometric constraints.

[0068] If the calculated actual positional relationship matches the preset function If the deviation exceeds the allowable safety tolerance, the central control unit determines that the nonlinear mechanical linkage mechanism has suffered a wear, jamming, or breakage fault, and triggers the emergency stop protection. The central control unit connects to the aforementioned sensors via an industrial fieldbus or analog I / O interface, and synchronously reads the status data of each sensor at a preset sampling frequency for logic control and process data recording.

[0069] Furthermore, this invention employs a dual-channel control strategy based on a hybrid mechanical and hydraulic drive, which enables precise management of the forming process by executing kinematic coupling control and hydraulic active compensation control in parallel through a central control unit.

[0070] The first channel is the kinematic coupling channel, which constitutes the volumetric feedforward control loop of the system, specifically: The central control unit is based on the preset axial feed rate curve. The system sends motion commands to the axial feed mechanism, and the displacement detection sensor collects the pusher position of the axial feed mechanism in real time. The motion of the axial feed mechanism is fed back to the central control unit to maintain the accuracy of the axial feed motion. In this channel, the motion of the axial feed mechanism is directly driven by the rigid transmission of the nonlinear mechanical linkage mechanism to produce the corresponding compensation action of the volume compensation cylinder.

[0071] This channel utilizes the aforementioned mechanical modulation principle to generate a net mechanical flow rate within the fluid control volume. According to the aforementioned flow balance equation, the net mechanical flow rate is... It is the feed position Deterministic functions: in: These are the effective cross-sectional areas of the axial feed pusher and the compensating piston, as defined above. The aforementioned nonlinear geometric transmission ratio; : Axial feed rate.

[0072] In the elastic deformation range, the channel outputs zero net flow; in the plastic forming range, the channel outputs a filling flow that matches the theoretical deformation rate of the tube blank 50. This process does not rely on feedback from the pressure sensor and has hysteresis-free feedforward characteristics.

[0073] The second channel is a hydraulic active compensation channel, forming the system's pressure feedback control loop, specifically: The central control unit receives real-time hydrostatic pressure signals from pressure sensors. and compare it with the preset target pressure curve. In comparison, the central control unit adjusts the output power of the hydraulic power unit based on the pressure deviation value through frequency conversion drive or proportional valve control technology, thereby changing the active flow rate of the injected fluid control body. .

[0074] The control objective of this channel is to dynamically compensate for system errors and establish forming back pressure. During system operation, the active flow rate output by the hydraulic power unit is adjusted to address flow deviations caused by hydraulic medium compressibility, minor pipeline leaks, and inhomogeneities in the actual billet material. The following balance relationship must be satisfied: in: : The flow term required to establish the target rate of change of system pressure; Actual tube blank deformation flow rate With net mechanical flow The residual deviation term between them The central control unit synchronizes and coordinates the two channels mentioned above to achieve the control logic of mechanically handling large-flow volume replacement and hydraulically handling small-flow pressure fine adjustment. This reduces the dynamic response load of the hydraulic power unit and eliminates the pressure lag and overshoot phenomena commonly found in traditional single hydraulic closed-loop control.

[0075] Please see Figure 2 Based on the above, this invention provides a decoupled and coordinated control method for the axial feed force and internal pressure of pipe fitting bulging. This method is based on the aforementioned decoupled and coordinated control system for the axial feed force and internal pressure of pipe fitting bulging and includes the following steps: Step S100: Establish the volume evolution model and hardware configuration. This step constitutes the preset and initialization stage of the entire control method, aiming to establish the physical decoupling foundation. This stage specifically includes the following sub-steps: Sub-step S101: Establish the billet volume change model: Obtain the initial geometric parameters of the tube blank to be processed and the 3D CAD model data of the target part. Then, use finite element analysis software or volume integration algorithm to calculate the internal volume of the tube blank during the entire forming process. Feed displacement of the axial feed mechanism By establishing the corresponding relationships between changes, a curve depicting the volume change of the tube blank is constructed. And calculate its relationship with respect to the feed displacement. first derivative The derivative It characterizes the volume growth rate of the tube blank at different feed positions (i.e., the increase in internal cavity volume corresponding to a unit axial feed).

[0076] Sub-step S102, plan the mechanical transmission ratio distribution: Based on the volume change curve and its derivative, and combined with the aforementioned modified flow balance equation, the instantaneous geometric transmission ratio required for the nonlinear mechanical linkage mechanism is calculated. : 1. Set the net mechanical flow rate for the elastic deformation range of the tube blank (including the initial sealing section). When the value is zero, the target transmission ratio of the system is a constant. ,in, The effective cross-sectional area of ​​the pusher head of the axial feed mechanism. The effective cross-sectional area of ​​the piston in the volume compensation cylinder.

[0077] 2. Set the net mechanical flow rate for the plastic forming range of the tube blank. The target transmission ratio of the system is set to a positive value to compensate for the increase in plastic volume, and is thus a variable. ,in, The preset volume compensation coefficient has a value range of [value range missing]. , is used to define the proportion of mechanical compensation flow to total deformation flow.

[0078] Sub-step S103: Generate hardware manufacturing data: Based on the planned instantaneous geometric transmission ratio distribution Generate machining contour data or adjustment parameters for nonlinear mechanical linkage mechanisms: 1. If a cam-type embodiment is used, the instantaneous geometric transmission ratio... Along feed displacement Integrating the curves yields the cam lift curve, which is then converted into two-dimensional machining coordinate data for the forming guide surface of the variable curvature cam plate.

[0079] 2. If a linkage-type embodiment is adopted, the inverse kinematics model of the mechanism is used, according to... Solve for the ratio of the length of the input lever arm to the length of the output lever arm required for the swing lever assembly, and determine the locking position coordinates of the adjustable fulcrum assembly on the frame of the forming main unit.

[0080] Sub-step S104: Perform hardware configuration and system zero-point calibration. Based on the generated machining coordinate data, a corresponding variable curvature cam plate is manufactured or selected and rigidly fixed to the moving parts of the axial feed mechanism; or the position of the adjustable fulcrum assembly is adjusted and locked according to the locking position coordinates, the central control unit controls the axial feed mechanism to reset to the mechanical origin, the hydraulic power unit drives the compensation piston assembly of the volume compensation cylinder to move to the corresponding initial standby position, the preload of the reset bias assembly is adjusted, the mechanical clearance between the variable curvature cam plate and the driven roller assembly or between the hinge points of the connecting rod is eliminated, and the mechanical zero point calibration of the system is completed.

[0081] After completing the preset and initialization stage described in step S100, proceed to step S200: billet loading and initial liquid filling and sealing, specifically: The tube blank to be processed is placed into the forming mold of the forming host unit. The central control unit drives the pusher of the axial feed mechanism to abut against both ends of the tube blank to establish a mechanical sealing interface. The hydraulic power unit injects liquid medium into the internal cavity of the tube blank until the air is exhausted and the tube blank is filled. Thus, a closed fluid control body filled with incompressible fluid is formed between the internal cavity of the tube blank, the high-pressure guide pipe and the variable volume working chamber of the volume compensation cylinder.

[0082] After step S200 is completed, the system immediately proceeds to step S300: linear volumetric compensation feed. This step mainly covers the elastic deformation stage or low-pressure loading stage of the billet. Specifically: The central control unit drives the axial feed mechanism according to the process instructions, so that its pusher moves axially into the internal cavity of the tube blank. During this process, the axial feed mechanism drives the rigidly connected variable curvature cam plate to move linearly in sync.

[0083] The driven roller assembly of the nonlinear mechanical linkage mechanism maintains rolling contact with the linear holding section of the variable curvature cam plate. According to the planning in step S100 above, the linear holding section has a constant profile slope, which corresponds to a preset constant transmission ratio. .

[0084] Driven by the linear holding section, the compensation piston assembly of the volume compensation cylinder moves at a speed Retracting outwards, the system satisfies the complete decoupling condition: the effective cross-sectional area of ​​the axial feed mechanism pusher. With axial feed rate The product of these two is equal to the effective cross-sectional area of ​​the compensating piston in the volumetric compensating cylinder. With rollback speed The product of.

[0085] The physical process is as follows: the pusher of the axial feed mechanism penetrates into the interior of the tube blank, causing the volume of the fluid control body to decrease and generating a positive discharge flow; simultaneously, the compensation piston assembly of the volume compensation cylinder retracts, causing the volume of the fluid control body to increase and generating a negative absorption flow. Since the discharge flow and the absorption flow are equal in value and opposite in direction, the closed fluid control body composed of the tube blank inner cavity, the high-pressure guide pipe and the variable volume working chamber maintains a net flow of zero.

[0086] Therefore, the main booster pump of the hydraulic power unit only needs to maintain the basic back pressure and does not need to respond to the axial feed action. The movement of the axial feed mechanism no longer causes fluctuations in the fluid pressure inside the tube blank, thus achieving decoupling between the axial feed action and the internal pressure.

[0087] When the pusher of the axial feed mechanism moves beyond the preset elastic deformation range and into the plastic deformation range, step S400 is entered: nonlinear differential feeding. This step corresponds to the forming stage where the billet undergoes significant plastic expansion deformation. Specifically: During this stage, the central control unit continues to control the axial feed mechanism at a preset feed rate. As it advances axially, the axial feed mechanism drives the variable curvature cam plate to continue moving synchronously. Guided by the geometric contour of the variable curvature cam plate, the driven roller assembly of the nonlinear mechanical linkage mechanism smoothly transitions to the nonlinear modulation section.

[0088] The contour characteristics of the nonlinear modulation segment are based on the nonlinear transmission ratio planned in step S100 above. The retraction speed of the compensation piston assembly of the volume compensation cylinder, which is manufactured and driven by the nonlinear modulation section, is... It no longer maintains the original linear ratio, but is instead relative to the axial feed rate. Decrease.

[0089] At this point, the system enters the differential injection state: the positive displacement flow generated by the axial feed mechanism... Numerically greater than the negative absorption flow rate generated by the volumetric compensation cylinder The difference in flow rates between the two results in a positive net mechanical flow rate within the fluid control volume, denoted as . .

[0090] According to the aforementioned flow balance equation, this net mechanical flow... The calculation formula is: in: : This represents the net flow rate generated by the mechanical linkage mechanism to compensate for the deformation of the tube blank; The effective cross-sectional area of ​​the pusher head of the axial feed mechanism as defined above; The effective cross-sectional area of ​​the compensating piston in the volumetric compensation cylinder as defined above; The aforementioned definition refers to the plastic forming range with varying feed positions. Variable nonlinear geometric transmission ratio; The feed rate of the axial feed mechanism as defined above.

[0091] Due to nonlinear transmission ratio The design basis includes the volume evolution derivative of the tube blank. The above formula can be further expanded as follows: in: The volume compensation coefficient defined above ; The first derivative of the billet cavity volume with respect to the feed displacement, as defined above; The volume growth rate of the tube blank due to plastic deformation, as defined above.

[0092] The physical process is as follows: the excess fluid expelled by the pusher of the axial feed mechanism is directly pressed into the expanding internal cavity of the tube blank through the high-pressure guide pipe, actively filling the new volume generated by plastic deformation. This differential feeding mechanism realizes the direct conversion of the mechanical thrust of axial feed into the feeding hydraulic energy required for tube forming.

[0093] During this process, the hydraulic power unit only needs to replenish the net mechanical flow. With actual deformation flow rate The slight difference between them, or in the full compensation mode The system maintains a constant pressure without outputting flow. The forming process ends when the axial feed mechanism reaches the target endpoint and the tube blank conforms to the mold surface. When the axial feed mechanism reaches the preset axial feed endpoint position, and the outer wall surface of the tube blank is substantially in contact with the inner wall of the forming mold cavity, the subsequent steps are performed as follows: Step S500: High-pressure shaping and holding: The central control unit controls the axial feed mechanism to stop moving and maintain position lock. At this time, the nonlinear mechanical linkage mechanism is in a stationary state, the volume of the variable volume working chamber of the volume compensation cylinder remains locked, and the hydraulic power unit controls the main booster pump to output high-pressure fluid, further increasing the fluid pressure inside the tube blank to the preset shaping pressure value.

[0094] The forming pressure value is higher than the yield strength of the tube blank material, driving the wall material of the tube blank to completely conform to the tiny rounded corners and complex feature areas of the forming mold. After maintaining the forming pressure for a preset time, the elastic rebound tendency of the tube blank is eliminated, and it is finally shaped into the target tube fitting product.

[0095] Step S600: Depressurization and Demolding The central control unit controls the hydraulic power unit to open the unloading valve, rapidly releasing the fluid pressure inside the tube blank cavity and the closed fluid control body to atmospheric pressure. Subsequently, the forming mold opens, and the operator or robot arm removes the formed tube product. Step S700: System mechanical reset: The central control unit controls the axial feed mechanism to retract in the opposite direction of the axial feed until it returns to the mechanical origin. During the return stroke of the axial feed mechanism, the rigidly connected variable curvature cam plate or input linkage assembly moves in the opposite direction synchronously.

[0096] During this return stroke, under the elastic force of the reset bias assembly, the driven roller assembly or swing lever assembly closely adheres to the contour surface of the variable curvature cam plate or maintains contact with the kinematic pair of the linkage mechanism. This elastic constraint ensures that the nonlinear mechanical linkage mechanism will not generate mechanical disengagement or impact vibration during reverse motion.

[0097] Driven by the reverse following of the nonlinear mechanical linkage mechanism, the compensation piston assembly of the volume compensation cylinder resets from the retracted position to the initial extended position. The hydraulic medium in the variable volume working chamber flows back to the oil tank of the hydraulic power unit through the return oil branch of the hydraulic system or the switching valve. When the axial feed mechanism and the volume compensation cylinder have both returned to the initial state, the system is ready to carry out the next forming cycle of the tube blank.

[0098] Furthermore, in specific implementation, the intelligent decoupling algorithm operated by the central control unit is based on the following augmented state equation: Define state variables ,in For unmodeled system disturbances (including mechanical friction nonlinearity and volume change deviations caused by pipe anisotropy); The algorithm estimates the disturbance using the following observer equation. : in is the observer gain matrix.

[0099] The final control voltage output to the hydraulic power unit Determined by the following formula: in, The feedforward control quantity is calculated based on the constraint reference model. This refers to the control gain coefficient of the hydraulic system. This is a decoupling compensation term used to offset generalized disturbances.

[0100] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A decoupled and coordinated control system for the axial feed force and internal pressure of a pipe fitting during bulging, characterized in that, include: The forming main unit includes a forming mold with a forming cavity and an axial feed mechanism configured to move along the axis of the tube blank, the axial feed mechanism having a moving component that generates axial feed displacement; A hydraulic power unit is configured to inject a liquid medium into the internal cavity of the tube blank and establish forming pressure; The central control unit is configured to send control commands to the axial feed mechanism and the hydraulic power unit; A variable transmission ratio volume modulation unit is disposed between the axial feed mechanism and the internal fluid circuit of the tube blank; The variable transmission ratio volume modulation unit includes a volume compensation cylinder and a nonlinear mechanical linkage mechanism; The volume compensation cylinder has a hydraulic working chamber in fluid communication with the internal cavity of the tube blank, and has a movable component capable of changing the volume of the hydraulic working chamber. The nonlinear mechanical linkage mechanism physically connects the moving part of the axial feed mechanism with the movable part of the volume compensation cylinder; The nonlinear mechanical linkage mechanism is configured to establish a rigid position mapping relationship between the axial feed displacement of the axial feed mechanism and the volume adjustment movement of the volume compensation cylinder, so that when the axial feed mechanism feeds into the tube blank, it synchronously drives the volume compensation cylinder to change the volume of the hydraulic working chamber to absorb or discharge fluid.

2. The decoupled and coordinated control system for the axial feed force and internal pressure of a pipe fitting bulging process according to claim 1, characterized in that: The volume compensation cylinder includes a cylinder body assembly and a compensation piston assembly that is coaxially slidably disposed therein; The compensation piston assembly divides the internal space of the cylinder assembly into a variable-capacity working chamber and a back pressure balance chamber. The variable-capacity working chamber is connected in parallel with the internal cavity of the tube blank through a high-pressure flow guide pipe, so that the variable-capacity working chamber, the high-pressure flow guide pipe and the internal cavity of the tube blank together constitute a closed fluid control body; The compensation piston assembly includes a drive piston rod extending to the outside of the cylinder assembly, the drive piston rod being rigidly connected to the nonlinear mechanical linkage mechanism.

3. The decoupled and coordinated control system for the axial feed force and internal pressure of a pipe fitting bulging process according to claim 2, characterized in that: The back pressure balancing chamber is provided with a fluid interface leading to the low-pressure side or the atmospheric environment. The hydraulic power unit is connected to the closed fluid control body via a main inlet pipeline, and the hydraulic power unit is configured to supplement the pressure of the closed fluid control body to establish the required flow difference according to the instructions of the central control unit.

4. The decoupled and coordinated control system for axial feed force and internal pressure of pipe fitting bulging according to claim 2, characterized in that: The nonlinear mechanical linkage mechanism adopts a cam drive architecture, including: A variable curvature cam plate is rigidly fixed to the moving part of the axial feed mechanism and has a shaped guide surface. The driven roller assembly is rotatably connected to the end of the drive piston rod and abuts against the forming guide surface; A reset biasing assembly is configured to apply a biasing force to the compensating piston assembly to maintain continuous contact between the driven roller assembly and the forming guide surface.

5. The decoupled and coordinated control system for the axial feed force and internal pressure of a pipe fitting bulging according to claim 2, characterized in that: The nonlinear mechanical linkage mechanism adopts a linkage transmission structure, including: An adjustable fulcrum assembly is fixedly mounted on the frame of the forming main unit; The swing lever assembly is rotatably mounted on the adjustable fulcrum seat assembly via a central pivot. The input linkage assembly is hinged at both ends to the moving part of the axial feed mechanism and one end of the swing lever assembly, respectively. The output linkage assembly is hinged at both ends to the other end of the swing lever assembly and the drive piston rod, respectively. The adjustable fulcrum assembly is configured to adjust the position of the central pivot on the swing lever assembly to change the length ratio of the input lever arm to the output lever arm.

6. The decoupled and coordinated control system for the axial feed force and internal pressure of a pipe fitting bulging according to claim 4, characterized in that: The forming guide surface is distributed along the axial direction with linear holding sections and nonlinear modulation sections; The forming process of the tube blank is defined by an elastic deformation range and a plastic forming range; the linear holding section has a constant profile slope and is configured to make the absorption flow rate generated by the volume compensation cylinder due to the retraction movement equal to the discharge flow rate generated by the axial feed mechanism due to the feed movement when the tube blank is in the elastic deformation range, thereby maintaining the net flow rate of the fluid control body at zero. The nonlinear modulation segment has a varying profile slope and is configured such that when the tube blank is in the plastic forming range, the absorption flow rate generated by the volume compensation cylinder is less than the discharge flow rate generated by the axial feed mechanism, thereby generating a positive net mechanical flow rate inside the fluid control body.

7. The decoupled and coordinated control system for the axial feed force and internal pressure of a pipe fitting bulging according to claim 1, characterized in that: The instantaneous geometric transmission ratio of the nonlinear mechanical linkage mechanism is determined based on the ratio of the effective cross-sectional area of ​​the pusher of the axial feed mechanism to the effective cross-sectional area of ​​the compensating piston of the volume compensation cylinder; Furthermore, when the tube blank is in the plastic forming range, the instantaneous geometric transmission ratio is also configured to be related to the rate of change of the tube blank's internal volume with respect to the feed displacement, so that the net mechanical flow generated by the nonlinear mechanical linkage mechanism matches the volume growth rate of the tube blank due to plastic deformation.

8. The decoupled and coordinated control system for axial feed force and internal pressure of pipe fitting bulging according to claim 1, characterized in that: It also includes a sensor feedback network, which comprises: A displacement detection sensor is configured to measure the axial feed displacement of the axial feed mechanism in real time; A pressure sensor is configured to measure the hydrostatic pressure of the fluid in the internal fluid circuit of the tube blank in real time; A piston position monitoring sensor is configured to measure the actual retraction displacement of the compensation piston in the volume compensation cylinder in real time.

9. The decoupled and coordinated control system for the axial feed force and internal pressure of a pipe fitting bulging according to claim 8, characterized in that: The central control unit is configured to store the theoretical position mapping function of the nonlinear mechanical linkage mechanism; The central control unit compares the axial feed displacement collected by the displacement detection sensor with the actual retraction displacement collected by the piston position monitoring sensor in real time. If the correspondence between the two deviates from the theoretical position mapping function by more than a preset tolerance, the nonlinear mechanical linkage mechanism is determined to have malfunctioned and a shutdown protection is triggered.

10. A decoupled and coordinated control method for the axial feed force and internal pressure of a pipe fitting during bulging, characterized in that, The system based on any one of claims 1 to 9 is executed, comprising the following steps: Step S100: Based on the volume evolution law of the tube blank to be processed, plan the mechanical transmission ratio distribution of the nonlinear mechanical linkage mechanism, and configure the geometric parameters of the nonlinear mechanical linkage mechanism accordingly. Step S200: Load the tube blank into the forming mold and inject a liquid medium into the tube blank to establish a closed fluid control body; Step S300: Control the axial feed mechanism to perform axial feed, and at the same time drive the volume compensation cylinder to retract in a linear proportion through the nonlinear mechanical linkage mechanism, so that the flow rate absorbed by the volume compensation cylinder offsets the flow rate displaced by the axial feed mechanism, and maintains the net flow rate of the closed fluid control body at zero. Step S400: When the axial feed mechanism enters the plastic forming zone, the nonlinear mechanical linkage mechanism drives the volume compensation cylinder to retract in a nonlinear proportion, generating a positive net mechanical flow to fill the new volume generated by the plastic deformation of the tube blank. Step S500: Control the axial feed mechanism to stop moving, and control the hydraulic power unit to increase the pressure to shape the tube blank.

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