Cylinder control method based on four-imaginary-constellation limited displacement pump and proportional back pressure valve coordination

Abstract

The present application is suitable for the technical field of oil cylinder control, and provides an oil cylinder control method based on cooperation of a four-quadrant limited displacement pump and a proportional back pressure valve, comprising the following steps: S1, a control system acquires state parameters in real time; S2, a working quadrant and working condition are determined; S3, pump control is dominant control in normal working conditions; S4, cooperative control in abnormal working conditions; S5, working condition switching control, the device solves the problems of instability and insufficient safety of pump control type oil cylinder under complex working conditions, the method realizes the complementary advantages of pump control and valve control through pump valve cooperative control strategy, introduces a back pressure valve for auxiliary control under special working conditions, ensures the stability and safety of the control system, and plays the characteristics of four-quadrant motor-pump unit fast response and reversible operation, and the characteristics of proportional valve continuous adjustment, so that the oil cylinder can be accurately controlled when driving or regenerative braking, the throttling loss of the hydraulic system is reduced to the minimum, and the response efficiency of the engineering machinery actuator control is improved.

Description

Technical Field

[0001] This invention relates to the field of hydraulic cylinder control technology, and more specifically, to a cylinder control method based on the coordination of a four-quadrant displacement pump and a proportional back pressure valve. Background Technology

[0002] As the core actuator of a hydraulic system, the hydraulic cylinder is widely used in heavy-duty operations such as construction machinery and industrial automation. Its control performance directly determines the equipment's operating accuracy, stability, and energy efficiency. The core requirement of hydraulic cylinder control is to precisely regulate the movement speed, displacement position, and output force according to operating commands and changes in working conditions, while adapting to complex scenarios such as variable loads and energy recovery, achieving rapid response and precise tracking.

[0003] Currently, traditional hydraulic cylinder control is mainly divided into two categories: valve control and pump control. Valve control systems offer fast response and high control precision, but suffer from severe throttling losses, high energy consumption, and significant heat generation. Pump control systems use a motor-driven four-quadrant pump as the core control unit. The core logic is to directly control the output flow and pressure of the hydraulic pump by adjusting the motor's speed, direction, and torque through the controller, thereby achieving precise control of the cylinder's movement. The pump control method fully utilizes the four-quadrant operating characteristics of the motor and pump unit, supporting forward drive (such as cylinder lifting and retraction) and regenerative braking (such as energy recovery when the load drives the cylinder to descend). It is particularly suitable for scenarios with high loads, continuous operation, and energy recovery requirements, and is widely used in construction machinery and heavy-duty automated equipment. Its control process relies on a closed-loop algorithm, dynamically adjusting the motor output by collecting parameters such as motor speed, current, cylinder displacement, and load pressure to track preset cylinder speed or pressure targets.

[0004] While pump-controlled hydraulic cylinders offer advantages such as high energy efficiency and four-quadrant operation, they also present stability and safety issues under complex operating conditions. Specifically, they are prone to loss of control under overload conditions. When the cylinder is driven by external forces such as gravity (e.g., a falling object), the load forces the cylinder to move faster than the pump's flow capacity. Motor speed and torque regulation alone cannot provide effective damping, easily leading to cylinder overspeed and loss of control. This can also cause hydraulic cavitation, damaging system components. Furthermore, when the cylinder needs to move or hover precisely at extremely low speeds, factors such as motor speed control errors and internal system leaks can cause the cylinder to creep. Pump control logic alone cannot filter out minute speed fluctuations, affecting operational accuracy. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a hydraulic cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a hydraulic cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve, comprising the following steps: S1. The control system acquires status parameters in real time, including the target speed control command of the hydraulic cylinder, the position displacement sensor signal of the hydraulic cylinder piston and the hydraulic cylinder speed signal, the load pressure sensor signal, and the motor speed. The status parameters are used for subsequent working quadrant determination and working condition identification.

[0007] S2. Determine the working quadrant and working condition: Based on the status parameters collected by S1, the control system determines the current working state of the cylinder in the four quadrants and identifies the working state of the cylinder. The working state of the cylinder is divided into normal working condition and abnormal working condition.

[0008] S3. Pump-controlled dominance under normal operating conditions: Under normal operating conditions, a four-quadrant displacement pump-controlled dominance is adopted. The pump output is controlled by adjusting the motor speed and torque through closed-loop regulation to precisely adjust the cylinder speed and output force.

[0009] S4. Cooperative control of abnormal working conditions: When the cylinder is determined to enter an abnormal working condition, the control system introduces the proportional back pressure valve for cooperative control. That is, the opening of the proportional back pressure valve on the oil return side of the cylinder is adjusted according to the type of abnormal working condition, and the corresponding back pressure is applied to dampen the movement of the cylinder. The back pressure provides a reaction torque to ensure that the four-quadrant displacement pump is in a controlled state.

[0010] S5, Working Condition Switching Control: When the cylinder movement returns to normal working condition, the proportional back pressure valve gradually releases the back pressure, and the pump control returns to the normal control state of S3.

[0011] The present invention is further configured such that, in step S2, the four-quadrant working states are defined as follows: First quadrant: The cylinder extends and drives the load. The motor rotates forward to drive the four-quadrant limited displacement pump to pump oil. The load is a resistance load. The oil is output from the pump to the rodless chamber of the cylinder, and the oil in the rod chamber returns.

[0012] Second quadrant: The cylinder retracts and is reverse-driven by the load, the motor is in regenerative braking state, the load is an auxiliary load, the oil flows back from the rodless chamber of the cylinder to the pump, and the pump is in energy regeneration mode.

[0013] Third quadrant: The cylinder retracts and drives the load. The motor reverses to drive the four-quadrant limited displacement pump to pump oil. The load is a resistance load. The oil is output from the pump to the rod chamber of the cylinder, and the oil returns from the rodless chamber.

[0014] Fourth quadrant: The cylinder extends and is reverse-driven by the load, the motor is in regenerative braking state, the load is an auxiliary load, the oil flows back from the rod chamber of the cylinder to the pump, and the pump is in energy regeneration mode.

[0015] The present invention is further configured such that, in step S2, the abnormal working condition of the hydraulic cylinder is specifically determined according to four conditions: overload condition, extremely low speed crawling condition, hovering condition, and external disturbance oscillation condition.

[0016] Condition a: The condition for determining the overload condition is that the actual movement speed of the cylinder is opposite to the direction of the load force, and the actual speed of the cylinder is greater than the commanded speed.

[0017] Condition b: The condition for determining the extremely low-speed crawling condition is that the actual speed of the hydraulic cylinder is less than the commanded speed.

[0018] Condition c: The condition for determining the hovering condition is that the hydraulic cylinder is in the preset position and the actual speed of the hydraulic cylinder equals the commanded speed.

[0019] Condition d: The condition for determining the external disturbance oscillation condition is as follows: Based on the actual cylinder speed signal and load pressure signal, calculate the oscillation amplitude in the high-frequency band. When the high-frequency oscillation amplitude continuously exceeds the preset oscillation threshold and the duration reaches the preset time, it is determined that the external disturbance oscillation condition has been entered.

[0020] The present invention is further configured such that, in step S3, the target speed and target torque of the motor are given by the closed-loop control algorithm, and the output flow and pressure of the four-quadrant limited displacement pump are adjusted by tracking the target speed and torque, thereby realizing the tracking of the cylinder speed or pressure.

[0021] The present invention is further configured such that the coordinated control of abnormal operating conditions in step S4 is more specifically defined as follows: S41. Cooperative control under overload conditions: The control system calculates the opening control signal of the proportional back pressure valve through a proportional-derivative algorithm based on the deviation and differential of the actual speed and commanded speed of the cylinder. It adjusts the proportional back pressure valve on the oil return side of the cylinder to the preset opening, applies the corresponding back pressure to dampen the movement of the cylinder, provides reaction torque, and ensures the controlled operation of the four-quadrant displacement pump.

[0022] S42. Coordinated control of ultra-low speed crawling and hovering conditions: The control system calculates the opening control signal of the proportional back pressure valve through a proportional-integral algorithm based on the deviation between the actual speed and the commanded speed of the hydraulic cylinder and the integral of the deviation. The opening of the proportional back pressure valve is reduced to increase the motion damping, so that the oil circuit forms a hydraulic damping control loop, filtering out small speed fluctuations and ensuring that the hydraulic cylinder moves smoothly or maintains a stable position.

[0023] S43. Coordinated control under external disturbance and oscillation conditions: Implement coordinated anti-oscillation control of pumps and valves.

[0024] The present invention is further configured such that step S43 specifically comprises the following steps: S431, Oscillation State Identification: Real-time analysis of the oscillation frequency and amplitude of cylinder speed and pressure signals.

[0025] S432, Pump control mode switching and parameter adjustment: The drive motor of the four-quadrant limited displacement pump is switched from the pump control-dominated control under normal operating conditions in step S3 to the cooperative control under abnormal operating conditions based on oscillation feedback. The torque or speed control command of the motor is dynamically adjusted according to the identified oscillation characteristics in order to actively suppress oscillation through pump output.

[0026] S433, Valve-controlled Co-damping Injection: Synchronously adjust the opening of the proportional back pressure valve, and inject adjustable hydraulic damping into the control system based on the oscillation characteristics, co-acting with the adjustment action on the pump control side to jointly attenuate the oscillation.

[0027] The present invention is further configured such that the dynamic adjustment based on oscillation characteristics in steps S432 and S433 employs an adaptive control algorithm. The adaptive control algorithm takes the amplitude and frequency of the oscillation signal as input, and through preset fuzzy logic rules combined with a neural network model, calculates and dynamically adjusts the matching combination of pump control commands and proportional back pressure valve opening commands online.

[0028] The present invention is further configured such that the more specific steps of step S5, the operating condition switching control, are as follows: S51, back pressure gradually released: The control system controls the proportional back pressure valve to gradually increase the opening degree according to the working condition recovery signal, so that the back pressure drops to the preset normal back pressure threshold at a constant speed. The normal back pressure threshold is matched with the preset static judgment threshold to ensure that the back pressure release process is adapted to the normal motion state of the cylinder speed returning to above the above.

[0029] S52, Pump control system switching: When the back pressure drops to the preset normal back pressure threshold and the actual speed of the cylinder is stable above the preset static judgment threshold, the pump control system officially returns to the normal control state described in S3, and the control system switches the control strategy synchronously to ensure the tracking of cylinder speed and output force.

[0030] The present invention is further configured such that, in step S1, the control system includes a four-quadrant displacement pump, a motor driving the four-quadrant displacement pump, a hydraulic cylinder, a proportional back pressure valve connected to the return oil lines of the rod chamber and rodless chamber of the hydraulic cylinder respectively, a displacement sensor for detecting the displacement speed of the hydraulic cylinder, a pressure sensor for detecting the pressure of the rodless chamber and rod chamber of the hydraulic cylinder, a speed sensor for detecting the speed of the motor, and a control module.

[0031] The control module is connected to the motor, proportional back pressure valve, displacement sensor, pressure sensor and speed sensor.

[0032] The present invention is further configured such that when the hydraulic cylinder is determined to be in an overload condition, the control module adjusts the opening of the proportional back pressure valve on the oil return side of the hydraulic cylinder and applies adjustable back pressure to dampen the movement of the hydraulic cylinder, thereby ensuring that the four-quadrant limited displacement pump operates under control.

[0033] When the hydraulic cylinder is determined to enter the extremely low speed crawling or hovering conditions, the opening of the proportional back pressure valve is adjusted to increase the system damping, ensuring smooth cylinder movement and position maintenance.

[0034] When the hydraulic cylinder is determined to be in an external disturbance and oscillation condition, the control module executes pump-valve coordinated anti-oscillation control, synchronously adjusts the control parameters of the four-quadrant limited displacement pump drive motor and the opening of the proportional back pressure valve, and injects adaptive damping into the control system to attenuate the oscillation.

[0035] In summary, this application includes at least one of the following beneficial technical effects: (1) Through the pump-valve coordinated control strategy, the advantages of pump control and valve control are complemented. That is, pump control is the main control, and back pressure valve is introduced for auxiliary control under special working conditions to ensure the stability and safety of the control system. It gives full play to the characteristics of rapid response and reversible operation of the four-quadrant motor-pump unit, as well as the characteristics of continuous adjustment of the proportional valve, so that the oil cylinder can be accurately controlled when driving forward or regenerative braking. This setting minimizes the throttling loss of the hydraulic system while ensuring dynamic performance, and improves the response efficiency of the actuator control of engineering machinery.

[0036] (2) The pump-valve coordinated control strategy can effectively solve the problem of external disturbance oscillation, which avoids the risk of valve core wear and electromagnetic component overheating caused by repeated opening and closing of the proportional back pressure valve, and ensures the tracking accuracy of cylinder speed and output force, thereby improving the reliability and stability of the control system. Attached Figure Description

[0037] Fig. 1 This is a flowchart of the hydraulic cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve according to the present invention.

[0038] Fig. 2 This is a flowchart of the control system in this invention.

[0039] Fig. 3 This is a graph showing the integrated oscillation index and threshold curve in this invention. Detailed Implementation

[0040] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0041] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0042] Please see Figs. 1-3 The present invention provides the following technical solutions: Example 1: A cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve, comprising the following steps: S1. The control system acquires status parameters in real time, including the target speed control command of the hydraulic cylinder, the position displacement sensor signal of the hydraulic cylinder piston and the hydraulic cylinder speed signal, the load pressure sensor signal, and the motor speed. The status parameters are used for subsequent working quadrant determination and working condition identification.

[0043] A dynamic model is established based on the acquired state parameters.

[0044] In the dynamic model, the continuity equation for the cylinder flow rate is as follows: Hydraulic cylinders are divided into rodless chambers. And rod-shaped cavity.

[0045] When the hydraulic cylinder extends, the rodless chamber... and rod cavity The formula is as follows:

[0046]

[0047] During the retraction motion of the hydraulic cylinder, the rodless chamber and rod cavity The formula is as follows:

[0048]

[0049] In the formula, The output flow rate of the four-dimensional displacement pump is limited. The flow rate through the proportional back pressure valve, For leaked flow within the system, and These are the effective areas of the rodless cavity and the rod cavity, respectively. and represent the pressures in the rodless chamber and rod chamber, respectively, i.e., the pressures that change with time. and These refer to the control volume between the chamber and the control valve, respectively. The effective bulk modulus of hydraulic oil. The instantaneous speed during the extension and retraction of the hydraulic cylinder.

[0050] S2. Determine the working quadrant and working condition: Based on the status parameters collected by S1, the control system determines the current working state of the cylinder in the four quadrants and identifies the working state of the cylinder. The working state of the cylinder is divided into normal working condition and abnormal working condition.

[0051] S21. Based on the collected state parameters, the formula for calculating the hydraulic cylinder load force is as follows:

[0052] In the formula, This refers to the equivalent total mass of the piston and load. The viscous damping coefficient is... Coulomb friction, This is the load force, and its positive direction is the same as the piston extension direction. The instantaneous acceleration during the extension and retraction of the hydraulic cylinder. and The instantaneous pressure in the rodless and rod-type chambers.

[0053] S22. Determine the four-quadrant state: Based on the directional relationship between the actual speed of the hydraulic cylinder and the load force, that is, defining the piston extension direction as the positive direction, determine the working quadrant of the hydraulic cylinder.

[0054] The specific identification strategy for the working quadrant is as follows: First quadrant: Cylinder speed > 0, load force > 0, cylinder extends and drives the load, motor rotates forward to drive the four-quadrant limited displacement pump to pump oil, load is a resistance load, oil is output from the pump to the rodless chamber of the cylinder, and oil returns from the rod chamber.

[0055] Second quadrant: Cylinder speed < 0, load force >0, the cylinder retracts and is reverse-driven by the load, the motor is in regenerative braking state, the load is an auxiliary load, the oil flows back from the rodless chamber of the cylinder to the pump, and the pump is in energy regeneration mode.

[0056] Third quadrant: Cylinder speed < 0, load force When the value is less than 0, the cylinder retracts and drives the load. The motor reverses and drives the four-quadrant limited displacement pump to pump oil. The oil is output from the pump to the rod chamber of the cylinder, and the oil in the rodless chamber returns to the cylinder.

[0057] Fourth quadrant: Cylinder speed > 0, load force <0, the cylinder extends and is reverse-driven by the load, the motor is in regenerative braking state, the load is an auxiliary load, the oil flows back from the rod chamber of the cylinder to the pump, and the pump is in energy regeneration mode.

[0058] S23. Identify the working status of the hydraulic cylinder. The working status of the hydraulic cylinder is divided into normal working conditions and abnormal working conditions.

[0059] S3. Pump-controlled dominance under normal operating conditions: Under normal operating conditions, a four-quadrant displacement pump-controlled dominance is adopted. The pump output is controlled by adjusting the motor speed and torque through closed-loop regulation to precisely adjust the cylinder speed and output force.

[0060] In step S3, the target speed and target torque of the motor are given by the closed-loop control algorithm. The control system receives the actual speed signal of the hydraulic cylinder in real time and compares it with the target speed command input by external operation. It calculates the deviation between the two and then processes the deviation using a combination of proportional-derivative and proportional-integral algorithms.

[0061] The proportional action provides an immediate and proportional response to any deviation in speed or force, while the integral action provides cumulative compensation for persistent, small deviations. The differential action senses the trend and rate of deviation change and applies a reverse inhibitory force before the deviation is about to expand, effectively smoothing out fluctuations and preventing overshoot.

[0062] Based on the magnitude of the deviation, the duration of the deviation, and the rate of change of the deviation, a control quantity is calculated. This control quantity is then converted into a target speed command or a target torque command for the drive motor. By tracking the target speed and torque, the output flow and pressure of the four-quadrant displacement pump are adjusted, thereby achieving the tracking of the cylinder speed or pressure.

[0063] S4. Cooperative control of abnormal working conditions: When the cylinder is determined to enter an abnormal working condition, the control system introduces the proportional back pressure valve for cooperative control. That is, the opening of the proportional back pressure valve on the oil return side of the cylinder is adjusted according to the type of abnormal working condition, and the corresponding back pressure is applied to dampen the movement of the cylinder. The back pressure provides a reaction torque to ensure that the four-quadrant displacement pump is in a controlled state.

[0064] The specific criteria for determining abnormal operating conditions are as follows: Abnormal operating conditions of hydraulic cylinders specifically include overload conditions, extremely low-speed crawling conditions, hovering conditions, and external disturbance and vibration conditions.

[0065] Condition a: The condition for determining the overload condition is that the actual movement speed of the cylinder is opposite to the direction of the load force, and the actual speed of the cylinder is greater than the commanded speed.

[0066] Condition b: The condition for determining the extremely low-speed crawling condition is that the actual speed of the hydraulic cylinder is less than the commanded speed.

[0067] Condition c: The condition for determining the hovering condition is that the hydraulic cylinder is in the preset position and the actual speed of the hydraulic cylinder equals the commanded speed.

[0068] Condition d: The condition for determining the external disturbance oscillation condition is as follows: Based on the actual cylinder speed signal and load pressure signal, calculate the oscillation amplitude in the high-frequency band. When the high-frequency oscillation amplitude continuously exceeds the preset oscillation threshold and the duration reaches the preset time, it is determined that the external disturbance oscillation condition has been entered.

[0069] The more specific steps of the coordinated control of abnormal operating conditions in step S4 are as follows: S41. Cooperative control under overload conditions: The control system calculates the opening control signal of the proportional back pressure valve through a proportional-derivative algorithm based on the deviation and differential of the actual speed and commanded speed of the cylinder. It adjusts the proportional back pressure valve on the oil return side of the cylinder to the preset opening, applies the corresponding back pressure to dampen the movement of the cylinder, provides reaction torque, and ensures the controlled operation of the four-quadrant displacement pump.

[0070] Specifically, the output of the proportional-derivative controller is determined by a control quantity proportional to the magnitude of the current speed deviation and a control quantity proportional to the rate of change of the speed deviation. The proportional coefficient determines the instantaneous strength of the response deviation, while the derivative coefficient is used to predict the trend of the deviation and apply advance correction.

[0071] When the actual speed of the hydraulic cylinder exceeds the commanded speed, resulting in a positive speed deviation, the proportional control circuit immediately generates a control signal that reduces the opening of the proportional back pressure valve. The magnitude of this signal is proportional to the magnitude of the deviation, thereby establishing a base back pressure in the return oil circuit corresponding to the degree of overspeed, generating a damping force to suppress overspeed. At the instant the overload begins, the speed increases rapidly, and the rate of change of the deviation is large. At this time, the derivative circuit outputs a strong control signal, prompting the proportional back pressure valve to further and rapidly reduce its opening, thereby injecting a larger damping force in advance, effectively suppressing the rapid increase in speed, preventing overshoot, and improving the system's response speed and stability.

[0072] S42. Coordinated control of ultra-low speed crawling and hovering conditions: The control system calculates the opening control signal of the proportional back pressure valve through a proportional-integral algorithm based on the deviation between the actual speed and the commanded speed of the hydraulic cylinder and the integral of the deviation. The opening of the proportional back pressure valve is reduced to increase the motion damping, so that the oil circuit forms a hydraulic damping control loop, filtering out small speed fluctuations and ensuring that the hydraulic cylinder moves smoothly or maintains a stable position.

[0073] Specifically, the output of the proportional-integral controller is the sum of a control quantity proportional to the current deviation and a control quantity proportional to the cumulative value of the deviation over time. The proportional coefficient provides a fast response, while the integral coefficient eliminates static error by continuously accumulating the deviation.

[0074] When the hydraulic cylinder begins to move at extremely low speed due to a minor disturbance, resulting in a slight deviation, the proportional circuit will output a corresponding signal to fine-tune the opening of the back pressure valve to quickly counteract the disturbance. The integral circuit continuously accumulates historical deviation values. For extremely low-speed crawling and hovering conditions, the integral circuit will gradually adjust its output over time by continuously accumulating these minor deviations, thereby continuously correcting the opening of the proportional back pressure valve until all accumulated deviations are fully compensated, ultimately eliminating the steady-state error.

[0075] S43. Coordinated control under external disturbance and oscillation conditions: Implement coordinated anti-oscillation control using pump control and valve control.

[0076] The specific collaborative control process for external disturbance oscillation conditions is as follows: S431, Oscillation State Recognition: Limit the preset vibration amplitude and vibration time, and analyze the oscillation frequency and actual oscillation amplitude of the cylinder speed and pressure signals in real time.

[0077] S432, Pump control mode switching and parameter adjustment: The drive motor of the four-quadrant limited displacement pump is switched from the pump control-dominated control under normal operating conditions in step S3 to the cooperative control under abnormal operating conditions based on oscillation feedback. The torque or speed control command of the motor is dynamically adjusted according to the identified oscillation characteristics in order to actively suppress oscillation through pump output.

[0078] S433, Valve-controlled Co-damping Injection: Synchronously adjust the opening of the proportional back pressure valve, inject adjustable hydraulic damping into the control system based on the oscillation characteristics, and coordinate with the adjustment action of the pump control side to jointly dampen the oscillation.

[0079] In steps S432 and S433, the dynamic adjustment based on oscillation characteristics employs an adaptive control algorithm. This algorithm takes the actual oscillation amplitude and frequency as input, and uses preset fuzzy logic rules combined with a neural network model to calculate and dynamically adjust the matching combination of pump control commands and proportional back pressure valve opening commands online.

[0080] The specific control process based on the collected data is as follows: First, collect all sensor and command signals, and calculate based on the hydraulic cylinder load force formula. It then determines the current working quadrant and whether an abnormal working condition has been triggered based on the cylinder speed, and then makes a control decision.

[0081] Second, if no abnormal working condition is triggered, the pump control-led control in step S3 will be entered. That is, when the load is pushed horizontally (in the first and third quadrants), the control system will directly output the motor speed according to the deviation between the target speed command and the cylinder speed through a closed-loop control algorithm, so as to drive the cylinder to move smoothly.

[0082] Third, if the overload condition is triggered, the system enters the coordinated control of the overload condition in step S41, and the boom is lowered under load (second quadrant). When the cylinder speed is detected to be greater than the target speed command, the control system calculates and outputs a valve control signal to the corresponding proportional back pressure valve according to the proportional-derivative algorithm to establish back pressure, generate damping force, and restore the cylinder speed to the target speed command.

[0083] Fourth, if the extremely low-speed crawling or hovering condition is triggered, the system enters the coordinated control of the extremely low-speed crawling and hovering conditions in step S42. The control system calculates and outputs a valve control signal to the corresponding proportional back pressure valve to control the opening degree according to the proportional-integral algorithm, generating damping force. The generated variable damping is used to absorb the small fluctuations of the control system.

[0084] Fifth, if an external disturbance oscillation condition is triggered, then the coordinated control of the external disturbance oscillation condition in step S43 is entered, specifically as follows: Within a set vibration time window, a preset oscillation threshold is set, and the actual oscillation amplitude of the cylinder piston displacement is calculated. The oscillation frequency of the displacement signal is extracted through spectrum analysis. A comprehensive oscillation index is calculated based on the actual oscillation amplitude and oscillation frequency, and then compared with the preset oscillation threshold. When the oscillation index is less than or equal to the preset oscillation threshold, it is determined to be a small oscillation under normal operating conditions. Small oscillation can be determined to be the mechanical linkage vibration during the normal operation of the loader.

[0085] When the oscillation index exceeds the preset oscillation threshold, it is judged as an abnormal oscillation condition. Abnormal oscillation conditions will cause the cylinder to repeatedly exceed the load condition. The control system will repeatedly judge and, within the set time window, the proportional back pressure valve will repeatedly open and close, which will lead to problems such as accelerated wear of valve core and seals, and overheating and damage to electromagnetic control components, thereby affecting the accuracy of subsequent pump control and valve control coordination.

[0086] Therefore, by dynamically adjusting the motor's torque or speed control command based on the identified oscillation characteristics, the oscillation can be actively suppressed through the output of the four-quadrant displacement pump, and the opening of the proportional back pressure valve can be adjusted synchronously. Based on the oscillation characteristics, adjustable hydraulic damping is injected into the control system, which works in conjunction with the adjustment action on the pump control side to jointly attenuate the oscillation.

[0087] S5, Working Condition Switching Control: When the cylinder movement returns to normal working condition, the proportional back pressure valve gradually releases the back pressure, and the pump control returns to the normal control state of S3.

[0088] The more specific steps of step S5, the operating condition switching control, are as follows: S51. Gradual back pressure release: The control system controls the proportional back pressure valve to gradually increase its opening according to the working condition recovery signal, so that the back pressure drops to the preset normal back pressure threshold at a uniform speed, ensuring that the back pressure release process is adapted to the normal motion state of the cylinder speed.

[0089] S52, Pump Control System Switching: When the back pressure drops to the above-mentioned preset normal back pressure threshold, the pump control system officially returns to the normal control state of S3, and the control system synchronously switches the control strategy to ensure the tracking of cylinder speed and output force.

[0090] In Example 2, the above-mentioned hydraulic cylinder control method uses a control system to coordinate control, including pump control, valve control, and pump control and valve control to coordinate control of the stable extension and retraction of the hydraulic cylinder. The control system includes an execution and power unit, a sensing and detection unit, a valve control auxiliary unit, and a control core unit.

[0091] The actuation and power unit includes a hydraulic cylinder, a motor, and a four-quadrant displacement pump. The hydraulic cylinder has a rodless chamber and a rod chamber. The motor drives the four-quadrant displacement pump, which is connected to the rodless chamber and the rod chamber of the hydraulic cylinder through an oil circuit. It pumps oil in both directions to achieve four-quadrant operation of the hydraulic cylinder.

[0092] The sensing and detection unit includes a displacement sensor for detecting the displacement of the piston rod of the hydraulic cylinder, a pressure sensor for detecting the pressure in the rodless chamber and the pressure in the rod chamber of the hydraulic cylinder respectively, and a speed sensor for detecting the speed of the motor.

[0093] The valve-controlled auxiliary unit includes a proportional back pressure valve, which is connected in series in the return oil lines of the rod chamber and the rodless chamber of the hydraulic cylinder. The opening degree of the proportional back pressure valve can be continuously and proportionally adjusted by an electrical signal, thereby generating a controllable back pressure in the return oil line.

[0094] The control core unit includes a control module, which receives signals from displacement sensors, pressure sensors, speed sensors, and external manipulation commands. The control module runs the control algorithm of this invention and sends control signals to the motor driver and the proportional back pressure valve.

[0095] The basic working principle of this control system is that the control module calculates the required speed and force of the hydraulic cylinder in real time based on the operating commands and feedback from various sensors. Under normal operating conditions, by controlling the speed and torque of the motor, the four-quadrant limited displacement pump is driven to output the required flow and pressure, thereby controlling the hydraulic cylinder. At this time, the proportional back pressure valve maintains a large opening and the back pressure is very small. When the control system detects that an abnormal operating condition has been entered, the control module will calculate and output the corresponding control signal to the proportional back pressure valve on the corresponding return oil line according to the type of operating condition, adjust its opening to apply appropriate back pressure, and coordinate with the pump control to ensure the stability of the control system.

[0096] The specific implementation method of the control system is as follows: Step 1: Obtain real-time status parameters.

[0097] The control module continuously collects parameters: externally given operating commands, cylinder piston displacement, rodless chamber pressure, rod chamber pressure, and motor speed.

[0098] Step 2: Determine the working quadrant and operating conditions.

[0099] The quadrant determination process is as follows: by combining the direction of the control command, the actual direction of the cylinder's movement, the direction of the load force, and the working state of the motor, the quadrant in which the control system is currently located is determined.

[0100] The process of operating condition identification is as follows: compare the current state with a preset threshold to distinguish between normal operating conditions and abnormal operating conditions.

[0101] The logic for identifying abnormal operating conditions is as follows: When the hydraulic cylinder is determined to be in an overload condition, the control module adjusts the opening of the proportional back pressure valve on the oil return side of the hydraulic cylinder and applies adjustable back pressure to dampen the movement of the hydraulic cylinder, ensuring that the four-quadrant limited displacement pump operates under control.

[0102] When the hydraulic cylinder is determined to enter the extremely low speed crawling or hovering conditions, the opening of the proportional back pressure valve is adjusted to increase the damping of the control system, ensuring smooth movement and position maintenance of the hydraulic cylinder.

[0103] When the hydraulic cylinder is determined to be in an external disturbance and oscillation condition, the control module executes pump-valve coordinated anti-oscillation control, synchronously adjusts the control parameters of the four-quadrant displacement pump drive motor and the opening of the proportional back pressure valve, and injects adaptive damping into the control system to attenuate the oscillation.

[0104] Step 3: Pump control under normal operating conditions.

[0105] When the operating condition is determined to be normal, the control system adopts a pump-controlled mode. The control module, based on the target speed and target force of the hydraulic cylinder, controls the motor to track these targets via a servo driver, thereby driving the four-quadrant limited displacement pump to output flow and pressure, and controlling the movement of the hydraulic cylinder. At this time, the control signal of the proportional back pressure valve is set to its maximum value, corresponding to the maximum opening, so as to minimize the back pressure generated and reduce unnecessary throttling losses.

[0106] Step 4: Coordinated control of abnormal operating conditions.

[0107] When any abnormal operating condition is detected, the control system immediately enters the coordinated control mode. The control module first determines the return oil side of the current cylinder based on the quadrant determination result. For example, when the cylinder extends, the rod chamber is the return oil side, so the corresponding proportional back pressure valve is mainly controlled. When the cylinder retracts, the rodless chamber is the return oil side, so the corresponding proportional back pressure valve is mainly controlled. Then, according to the specific abnormal operating condition type, different control strategies are used to generate the control signal for the proportional back pressure valve, and the pump control command is adjusted synchronously according to the actual operating conditions.

[0108] First, coordinated control beyond load conditions.

[0109] A proportional-derivative (PD) control algorithm is employed, where the control signal is determined by both a proportional term and a derivative term. The proportional term is the product of the proportional coefficient and the difference between the actual speed and the commanded speed, while the derivative term is the product of the derivative coefficient and the rate of change of that speed difference. Under overload conditions, the difference between the actual speed and the commanded speed is typically negative.

[0110] The proportional-derivative algorithm calculates and outputs a small control signal, which reduces the opening of the proportional back pressure valve, thereby establishing sufficient back pressure on the return side. The back pressure acts on the effective working area of ​​the rod or rodless chamber of the cylinder, thus generating a corresponding damping force. This control method can prevent the hydraulic pump from becoming unstable due to being dragged by the load. On the pump control side, the corresponding motor switches to regenerative braking mode to smoothly absorb the energy generated during the load movement.

[0111] Second, coordinated control of extremely low-speed crawling and hovering conditions.

[0112] The proportional-integral control algorithm is adopted. The control signal is the product of the proportional coefficient and the deviation, and the product of the integral coefficient and the integral result of the deviation. The static error of the control system is eliminated by the integral action, while the proportional action is used to achieve a fast response to the deviation. The output control signal value is smaller, which drives the opening of the proportional back pressure valve to decrease accordingly. This establishes a stable and high back pressure in the hydraulic circuit, enhances the hydraulic damping of the control system, and achieves the extremely low-speed crawling state of the cylinder. It can also resist small external force disturbances when the control system is in a hovering state, ensuring the stability of the cylinder position.

[0113] Third, coordinated control of external disturbance and oscillation conditions.

[0114] First, oscillation state identification.

[0115] The real-time signal is analyzed by Fast Fourier Transform to identify the current dominant oscillation frequency and amplitude.

[0116] Secondly, pump control mode switching and parameter adjustment.

[0117] The control module switches the motor's control mode from the conventional mode to the active damping injection mode. For example, based on the oscillation frequency and amplitude, it dynamically modifies the gain of the motor torque loop or adds a torque compensation amount that is negatively correlated with the speed oscillation derivative, so that the pump control directly consumes the oscillation energy.

[0118] Secondly, valve-controlled coordinated damping injection.

[0119] Based on the same oscillation characteristics, an additional control signal for the proportional back pressure valve is generated through online calculation. The opening is dynamically fine-tuned so that the back pressure change it generates is inversely related to the oscillation speed. In this way, the oscillation energy is consumed through hydraulic damping. The damping injection actions of pump control and valve control are coordinated in terms of timing and vibration amplitude to achieve the oscillation attenuation effect.

[0120] An adaptive control algorithm is employed during the coordinated control operation under external disturbance and oscillation conditions. This algorithm takes the oscillation frequency and amplitude as input and uses a trained fuzzy neural network model. The fuzzy neural network model stores the mapping relationship between the optimal pump control parameter adjustment and valve opening adjustment under different oscillation characteristics. The control system can query this model online to obtain the appropriate combination of coordinated control commands, thus achieving intelligent oscillation suppression.

[0121] Step 5: Operating condition switching control.

[0122] When the control system detects that the abnormal operating conditions have disappeared, it initiates switching control.

[0123] First, the back pressure is gradually released.

[0124] The control module generates a ramp signal, which gradually increases the control signal of the proportional back pressure valve used for coordinated control under abnormal conditions from the current value to the maximum opening. The back pressure then decreases at a constant speed to the back pressure threshold under normal conditions. This process needs to be gradual to avoid sudden acceleration of the cylinder due to a sudden drop in back pressure.

[0125] Second, switch the pump control system.

[0126] During the back pressure release process, the calculation of pump control commands gradually transitions from the algorithm of the cooperative control mode back to the algorithm of the normal pump control dominant mode. When the back pressure drops to the normal threshold and the actual speed of the cylinder stabilizes within the normal range, the control module completes the flag switching, and the control system fully returns to the normal pump control dominant state in step three.

[0127] The specific operation process is as follows: Normal lifting (normal working condition): The operating command requires the hydraulic cylinder to lift the load at a constant speed. The control system judges it as a normal working condition. The control module increases the speed by adjusting the forward rotation of the motor, which drives the four-quadrant top displacement pump to supply oil to the rodless chamber. The hydraulic cylinder lifts smoothly. During this process, the proportional back pressure valve opens to its maximum and the back pressure is extremely low.

[0128] Rapid load descent (overload condition): When a heavy object needs to be lowered quickly, the control command outputs the lowering speed. At this time, the load gravity becomes an auxiliary load. The control system immediately identifies the deviation of the actual speed from the command speed and determines that it has entered the overload condition. The control module controls the corresponding proportional back pressure valve to close the opening according to the proportional-derivative control algorithm, establish back pressure, generate an upward damping force, suppress the overspeed of the lowering, control the motor to enter the regenerative power generation state, smoothly control the pump speed, absorb the load potential energy, and the cylinder can lower the load smoothly at the command speed.

[0129] Position limitation (hovering condition): When the cylinder needs to stay at a certain height, the control system determines that it has entered the hovering condition. The control module maintains the corresponding proportional back pressure valve at a small opening according to the proportional-integral control algorithm, forming a stable static back pressure, which improves the position stiffness of the control system. Even if there is slight leakage or thermal expansion, the integral control can fine-tune the back pressure to compensate, thus achieving long-term position limitation.

[0130] Impact Encounter (External Disturbance Oscillation Condition): During the cylinder lifting process, a slight lateral collision suddenly occurs with the load, triggering high-frequency chattering of the cylinder piston rod. The sensor detects the high-frequency oscillation signal, and the control module quickly identifies it as an external disturbance oscillation condition. Based on the oscillation amplitude characteristics, the fuzzy neural network immediately outputs a set of instructions: increasing the motor torque loop gain by 20% and adding a torque compensation that is negatively correlated with the speed derivative. Simultaneously, it instructs the proportional back pressure valve opening to oscillate at a frequency of 5Hz with an amplitude of ±5%, inversely related to the speed. With the coordinated action of the pump and valve, the control system quickly dampens the oscillation and restores stable lifting.

[0131] like Fig. 3 As shown, this embodiment verifies the effectiveness of the coordinated control of pump control and valve control by monitoring changes in the overall oscillation index: The horizontal axis represents time, indicating the time progression of the hydraulic cylinder control process.

[0132] The vertical axis represents the comprehensive oscillation index, which is a quantitative indicator calculated based on the oscillation amplitude and oscillation frequency of the cylinder piston displacement.

[0133] The abnormal threshold line is the critical value for determining abnormal operating conditions caused by external disturbances and oscillations.

[0134] The normal threshold line is the critical value for determining normal operating conditions.

[0135] The waveform curve represents the real-time change curve of the comprehensive oscillation index.

[0136] The nodes marked by dashed lines represent the disturbance start node, control intervention node, and disturbance end node, corresponding to the key time points in the control process.

[0137] Fig. 3 middle: Pre-disturbance stage (0-3s): The comprehensive oscillation index is above the normal threshold line, and the control system is in the pump control dominant control state of step S3, which is a normal small-amplitude oscillation condition of the loader's conventional mechanical linkage.

[0138] Disturbance intervention stage (3s node, disturbance start line): External disturbances, including mechanical shaking of the loader due to uneven ground, act in the opposite direction on the hydraulic cylinder, the comprehensive oscillation index rises rapidly, deviates from the normal threshold line, and the control system begins to transition to abnormal working conditions.

[0139] Control Initiation Phase (4s Node, Control Intervention Line): When the comprehensive oscillation index exceeds the abnormal threshold, the control system determines that it has entered an abnormal operating condition due to external disturbance oscillation, triggering the pump-valve coordinated anti-oscillation control in step S43: First, pump control side: the drive motor of the four-quadrant limited displacement pump switches to the coordinated control of abnormal oscillation feedback conditions, and actively suppresses oscillation by dynamically adjusting torque and speed commands.

[0140] Second, valve control side: synchronously adjust the opening of the proportional back pressure valve and inject appropriate hydraulic damping into the control system.

[0141] With the combined effect of pump control and valve control, the overall oscillation index dropped rapidly.

[0142] Disturbance termination phase (7s node, disturbance termination line): The external disturbance disappears, the comprehensive oscillation index further decreases and stabilizes below the normal threshold line, the control system returns to normal operating conditions, and then the operating condition switching control of step S5 is executed: the proportional back pressure valve gradually increases its opening, releases the back pressure, and the pump control system returns to the normal control state of step S3.

[0143] The pump-valve coordinated control strategy can effectively solve the problem of external disturbances and oscillations. It avoids the risk of valve core wear and electromagnetic component overheating caused by repeated opening and closing of the proportional back pressure valve, and ensures the tracking accuracy of cylinder speed and output force, thereby improving the reliability and stability of the control system.

[0144] Obviously, the embodiments described above are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

Claims

1. A cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve, characterized in that, Includes the following steps: S1. The control system acquires status parameters in real time, including the target speed control command of the hydraulic cylinder, the position displacement sensor signal of the hydraulic cylinder piston and the hydraulic cylinder speed signal, the load pressure sensor signal, and the motor speed. The status parameters are used for subsequent working quadrant determination and working condition identification. S2. Determine the working quadrant and working condition: Based on the status parameters collected in S1, the control system determines the current working state of the cylinder in the four quadrants and identifies the working state of the cylinder. The working state of the cylinder is divided into normal working condition and abnormal working condition; the abnormal working conditions are overload working condition, extremely low speed crawling working condition, hovering working condition and external disturbance oscillation working condition. S3. Pump-controlled dominance under normal operating conditions: Under normal operating conditions, a four-quadrant displacement pump-controlled dominance is adopted. The pump output is controlled by adjusting the motor speed and torque through closed-loop regulation to precisely adjust the cylinder speed and output force. S4. Cooperative control of abnormal working conditions: When the cylinder is determined to enter an abnormal working condition, the control system introduces the proportional back pressure valve for cooperative control. That is, the opening of the proportional back pressure valve on the oil return side of the cylinder is adjusted according to the type of abnormal working condition, and the corresponding back pressure is applied to dampen the movement of the cylinder. The back pressure provides a reaction torque to ensure that the four-quadrant displacement pump is in a controlled state. The more specific steps of the coordinated control of abnormal operating conditions in step S4 are as follows: S41, Cooperative control beyond load conditions; S42, Coordinated control of ultra-low speed crawling and hovering conditions; S43. Coordinated control under external disturbance and oscillation conditions; The specific steps of step S43 are as follows: S431, Oscillation State Identification; S432, Pump control mode switching and parameter adjustment; S433, Valve-controlled Cooperative Damping Injection; The specific control process based on the collected data is as follows: Real-time acquisition of sensor signals determines operating conditions. Under normal operating conditions, pump control is dominant. When the load exceeds the limit, the proportional-derivative algorithm is used to adjust the proportional back pressure valve to generate damping and suppress overspeed. At extremely low speeds or when hovering, the proportional-integral algorithm is used to adjust the back pressure valve to increase damping and eliminate fluctuations. When there is external disturbance and oscillation, the comprehensive oscillation index is calculated through spectrum analysis. If the oscillation index exceeds the preset oscillation threshold, it is judged as abnormal. An adaptive control algorithm is used to simultaneously adjust the motor torque or speed and the back pressure valve opening. The pump and valve work together to inject damping, avoid valve core wear and overheating, and effectively attenuate oscillations. S5, Working Condition Switching Control: When the cylinder movement returns to normal working condition, the proportional back pressure valve gradually releases the back pressure, and the pump control returns to the normal control state of S3.

2. The cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve according to claim 1, characterized in that: In step S2, the four-quadrant working states are defined as follows: First quadrant: The cylinder extends and drives the load. The motor rotates forward to drive the four-quadrant limited displacement pump to pump oil. The load is a resistance load. The oil is output from the pump to the rodless chamber of the cylinder. The oil in the rod chamber returns to the cylinder. Second quadrant: The cylinder retracts and is reverse-driven by the load, the motor is in regenerative braking state, the load is an auxiliary load, the oil flows back from the rodless chamber of the cylinder to the pump, and the pump is in energy regeneration mode. Third quadrant: The cylinder retracts and drives the load. The motor reverses to drive the four-quadrant limited displacement pump to pump oil. The load is a resistance load. The oil is output from the pump to the rod chamber of the cylinder. The oil returns from the rodless chamber. Fourth quadrant: The cylinder extends and is reverse-driven by the load, the motor is in regenerative braking state, the load is an auxiliary load, the oil flows back from the rod chamber of the cylinder to the pump, and the pump is in energy regeneration mode.

3. The cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve according to claim 2, characterized in that: In step S2, four judgment conditions are set according to the abnormal working conditions of the hydraulic cylinder. Condition a: The condition for determining the overload condition is that the actual speed of the cylinder is opposite to the direction of the load force, and the actual speed of the cylinder is greater than the commanded speed. Condition b: The condition for determining the extremely low-speed crawling condition is that the actual speed of the hydraulic cylinder is less than the commanded speed; Condition c: The condition for determining the hovering condition is that the hydraulic cylinder is in the preset position and the actual speed of the hydraulic cylinder equals the commanded speed; Condition d: The condition for determining the external disturbance oscillation condition is: based on the actual speed signal of the hydraulic cylinder and the load pressure signal, calculate its oscillation amplitude in the high-frequency band; When the amplitude of high-frequency oscillation continuously exceeds the preset oscillation threshold and the duration reaches the preset time, it is determined that the external disturbance oscillation condition has been entered.

4. The cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve according to claim 1, characterized in that: In step S3, the target speed and target torque of the motor are given by the closed-loop control algorithm. By tracking the target speed and torque, the output flow and pressure of the four-quadrant limited displacement pump are adjusted, thereby achieving tracking of the cylinder speed or pressure.

5. The cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve according to claim 3, characterized in that: Step S41 is as follows: The control system calculates the opening control signal of the proportional back pressure valve based on the deviation and differential of the actual speed of the oil cylinder and the commanded speed, and adjusts the proportional back pressure valve on the oil return side of the oil cylinder to the preset opening, applies the corresponding back pressure to dampen the movement of the oil cylinder, provides the reaction torque, and ensures the controlled operation of the four-quadrant limited displacement pump. Step S42 is as follows: The control system calculates the opening control signal of the proportional back pressure valve based on the deviation between the actual speed of the oil cylinder and the commanded speed and the integral of the deviation, and reduces the opening of the proportional back pressure valve to increase the motion damping, so that the oil circuit forms a hydraulic damping control loop, filters out small speed fluctuations, and ensures that the oil cylinder moves smoothly or its position remains stable. Step S43 specifically involves: executing pump-valve coordinated anti-oscillation control.

6. The cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve according to claim 5, characterized in that: The specific steps of step S43 are as follows: Step S431 specifically involves: real-time analysis of the oscillation frequency and amplitude of the cylinder speed and pressure signals; Step S432 specifically involves: switching the drive motor of the four-quadrant limited displacement pump from the pump-controlled dominance in the normal operating condition of step S3 to the cooperative control based on oscillation feedback in the abnormal operating condition, and dynamically adjusting the torque or speed control command of the motor according to the identified oscillation characteristics, so as to actively suppress oscillation through pump output. Step S433 specifically involves: synchronously adjusting the opening of the proportional back pressure valve, injecting adjustable hydraulic damping into the control system based on the oscillation characteristics, and coordinating with the adjustment action on the pump control side to jointly dampen the oscillation.

7. The cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve according to claim 6, characterized in that: In steps S432 and S433, the dynamic adjustment based on oscillation characteristics employs an adaptive control algorithm. The adaptive control algorithm takes the amplitude and frequency of the oscillation signal as input, and uses preset fuzzy logic rules combined with a neural network model to calculate and dynamically adjust the matching combination of pump control commands and proportional back pressure valve opening commands online.

8. The cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve according to claim 3, characterized in that: The more specific steps of the operating condition switching control in step S5 are as follows: S51, back pressure gradually released: The control system controls the proportional back pressure valve to gradually increase the opening degree according to the working condition recovery signal, so that the back pressure drops to the preset normal back pressure threshold at a constant speed. The normal back pressure threshold is matched with the preset static judgment threshold to ensure that the back pressure release process is adapted to the normal motion state of the cylinder speed returning to above. S52, Pump control system switching: When the back pressure drops to the preset normal back pressure threshold and the actual speed of the cylinder is stable above the preset static judgment threshold, the pump control system officially returns to the normal control state described in S3, and the control system switches the control strategy synchronously to ensure the tracking of cylinder speed and output force.

9. The cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve according to claim 1, characterized in that: In step S1, the control system includes a four-quadrant displacement pump, a motor driving the four-quadrant displacement pump, a hydraulic cylinder, a proportional back pressure valve connected to the return oil lines of the rod chamber and rodless chamber of the hydraulic cylinder respectively, a displacement sensor for detecting the displacement speed of the hydraulic cylinder, a pressure sensor for detecting the pressure of the rodless chamber and rod chamber of the hydraulic cylinder, a speed sensor for detecting the motor speed, and a control module. The control module is connected to the motor, proportional back pressure valve, displacement sensor, pressure sensor and speed sensor.

10. The cylinder control method based on the coordinated operation of a four-quadrant displacement pump and a proportional back pressure valve according to claim 9, characterized in that: When the control module determines that the cylinder has entered an overload condition, it adjusts the opening of the proportional back pressure valve on the oil return side of the cylinder and applies adjustable back pressure to dampen the movement of the cylinder, ensuring that the four-quadrant limited displacement pump operates under control. When the hydraulic cylinder is determined to enter the extremely low speed crawling and hovering conditions, the opening of the proportional back pressure valve is adjusted to increase the system damping, ensuring smooth movement and position maintenance of the hydraulic cylinder. When the hydraulic cylinder is determined to be in an external disturbance and oscillation condition, the control module executes pump-valve coordinated anti-oscillation control, synchronously adjusts the control parameters of the four-quadrant limited displacement pump drive motor and the opening of the proportional back pressure valve, and injects adaptive damping into the control system to attenuate the oscillation.

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