EHA-based six-degree-of-freedom motion positioning platform control system and method

Abstract

The invention discloses an EHA-based six-degree-of-freedom motion positioning platform control system and method. The system comprises an EHA-based six-degree-of-freedom platform, an upper computer, a single-chip microcomputer controller, a displacement sensor, an attitude sensor, a data acquisition card and a motor driver. The six-degree-of-freedom platform is provided with a plurality of electro-hydrostatic actuators, and each electro-hydrostatic actuator is provided with a hydraulic cylinder and a direct current motor; the upper computer calculates the target length of each hydraulic cylinder under a target attitude based on a kinematics inverse solution algorithm, calculates the target displacement values of the driving cylinder and the driven cylinder, generates a corresponding duty ratio control instruction, outputs a PWM signal of a corresponding duty ratio to the motor driver, and the motor driver changes the output voltage and drives the direct current motor to perform speed regulation and reversing. And speed regulation reversing and position control are carried out on the electro-hydrostatic actuator. Spatial motion and positioning of the six-degree-of-freedom platform are achieved, trajectory planning is not needed, and the control process is simple and efficient.

Description

Technical Field

[0001] This invention relates to the field of six-degree-of-freedom platform control technology, specifically to a six-degree-of-freedom motion positioning platform control system and method based on EHA. Background Technology

[0002] Traditional six-degree-of-freedom (6DOF) platforms are typically driven by hydraulic cylinders, electric cylinders, pneumatic cylinders, or piezoelectric ceramics, and their control systems generally employ valve-controlled cylinders. Electro-hydraulic actuators (EHAs) offer advantages such as high power density and high energy efficiency. Using an EHA system as the drive system for a 6DOF platform overcomes the drawbacks of traditional electro-hydraulic systems, such as the high cost of electro-hydraulic servo valves, sensitivity to oil contamination, low energy utilization, and the need for a separate cooling system due to high oil temperatures.

[0003] Compared to pneumatic drives, EHA direct-drive six-degree-of-freedom platforms offer higher precision and simpler structure. Compared to electric drives, they have greater load capacity, higher energy efficiency, lower cost, and are easier to maintain. Using the EHA system as the drive component of a six-degree-of-freedom platform combines the advantages of the EHA system (high power density, high energy efficiency, and low maintenance cost) with the advantages of the six-degree-of-freedom platform (high rigidity, high precision, high load capacity, fast dynamic response, and low cumulative error). However, the current cooperative control strategy for six-degree-of-freedom platforms mainly uses interpolation algorithms. The longer the interpolation algorithm period, the greater the motion error. Generally, the shorter the period, the smaller the abrupt changes and deviations during motion, and the smaller the motion error. However, the interpolation algorithm has a large computational load, which can lead to system oscillations in complex motion processes. Summary of the Invention

[0004] To overcome the defects and shortcomings of existing technologies, this invention provides a six-degree-of-freedom motion positioning platform control system and method based on EHA. This invention performs master-slave collaborative control of hydraulic cylinders for the single-posture motion process of a six-degree-of-freedom motion platform, and realizes the spatial motion and positioning of the six-degree-of-freedom platform based on the BP-nonlinear PID control strategy. No trajectory planning is required, and the control process is simple and efficient.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a six-degree-of-freedom motion positioning platform control system based on EHA, comprising: an EHA-based six-degree-of-freedom platform, a host computer, a microcontroller, a displacement sensor, an attitude sensor, a data acquisition card, and a motor driver; The six-degree-of-freedom platform is equipped with multiple electro-hydraulic actuators, each of which includes a hydraulic cylinder and a DC motor. The motor driver is connected to the DC motor; The displacement sensor is located on one side of the hydraulic cylinder and is used to collect the displacement voltage signal of the hydraulic cylinder. The attitude sensor is used to acquire the real-time pose of the six-degree-of-freedom platform; The host computer calculates the target length of each hydraulic cylinder under the target posture based on the inverse kinematics algorithm, determines the active cylinder, and uses the target length as the target displacement value of the active cylinder. The driven cylinder length is calculated using the inverse kinematics algorithm and used as the target displacement value of the driven cylinder. The corresponding duty cycle control command is then generated. The microcontroller receives the duty cycle control command output by the host computer and outputs a PWM signal with the corresponding duty cycle to the motor driver. The motor driver changes the output voltage according to the PWM signal, drives the DC motor to perform speed regulation and commutation, and performs speed regulation, commutation and position control of the electro-hydraulic actuator to realize three-dimensional spatial motion and positioning.

[0006] As a preferred technical solution, the six-degree-of-freedom platform further includes: a moving platform, a first pad, a second pad, and a stationary platform. The moving platform is connected to the electro-hydraulic actuator through the first pad, and the electro-hydraulic actuator is connected to the stationary platform through the second pad.

[0007] As a preferred technical solution, the electro-hydraulic actuator further includes: a first ball joint, an integrated valve block, a gear pump, a pressure oil tank, and a second ball joint; The first ball joint and the second ball joint are located at both ends of the hydraulic cylinder. The first ball joint is connected to the moving platform through the first pad, and the second ball joint is connected to the stationary platform through the second pad. The DC motor is connected to the gear pump via a coupling. The gear pump is located in the pressure tank. The gear pump changes its displacement based on the speed of the DC motor. The flow rate discharged by the gear pump flows through the integrated valve block to the hydraulic cylinder. The stroke length of the hydraulic cylinder is adjusted based on the pump displacement.

[0008] As a preferred technical solution, the host computer calculates the control quantity based on the BP-nonlinear PID algorithm, which includes positional digital PID algorithm, anti-integral saturation algorithm, integral separation algorithm, variable speed integral algorithm, and correction coefficient algorithm. After inputting the previous control quantity, previous error value, target displacement value, current displacement value, and cumulative integral value, determine whether the control quantity has reached its maximum or minimum value. If so, use the anti-integral saturation algorithm; otherwise, determine whether the absolute value of the difference between the target displacement value and the current displacement value exceeds the set threshold. If so, use the integral separation algorithm; otherwise, determine whether the error value is within the variable speed integral range. If so, use the variable speed integral algorithm to calculate the integral value, calculate the control quantity using the positional PID algorithm, and determine whether the control quantity is less than 0. If so, use the correction coefficient algorithm; otherwise, output the control quantity. The PID parameters are adjusted based on the BP neural network, and the outputs of the neurons in the output layer of the BP neural network correspond to the control parameters of the PID controller.

[0009] As a preferred technical solution, the anti-integral saturation algorithm, before calculating the integral term, determines whether the value of the control quantity at the previous moment is within the interval [u]. min u max In addition, when the control quantity u at the previous moment (k-1) ≥u max At that time, the integral term only accumulates negative deviations, and the control quantity u from the previous moment... (k-1) min When the integral term accumulates only the positive deviation, the integral term only accumulates the positive deviation.

[0010] As a preferred technical solution, in the integral separation algorithm, when the deviation value exceeds the set threshold, the integral term is not accumulated.

[0011] As a preferred technical solution, in the variable speed integral algorithm, the accumulation speed of the integral term is changed to correspond to the magnitude of the deviation.

[0012] As a preferred technical solution, the expression for the correction coefficient algorithm is: ; in, The area of ​​the rodless cavity, For the area of ​​the rod cavity, , These represent the values ​​before and after the correction, respectively.

[0013] As a preferred technical solution, the expression for the positional digital PID algorithm is: ; Where kp is the proportional coefficient, ki is the integral coefficient, kd is the differential coefficient, k is the sampling number, and e(k) and e(k-1) are the deviation signals obtained at time k and time k-1, respectively.

[0014] As a preferred technical solution, the following steps are included: After inputting the target posture, the lengths of the six hydraulic cylinders under the final target posture are calculated using the inverse kinematics algorithm of the six-degree-of-freedom platform. Find the absolute value of the difference between the target length of the hydraulic cylinder and the actual length of the current hydraulic cylinder, and designate the hydraulic cylinder with the largest absolute value as the driving cylinder, and the rest as driven cylinders; The target displacement of the active cylinder is the length calculated from the final target attitude; The real-time attitude of the six-degree-of-freedom platform during motion is calculated using a modified version of the inverse kinematics algorithm. The length of the driven cylinder calculated by the inverse kinematics algorithm is used as the target displacement of the driven cylinder. ​The maximum value of the control quantity output by the control algorithm of the active cylinder or the maximum speed is limited; The host computer generates corresponding duty cycle control commands based on the control quantities. The microcontroller receives the duty cycle control commands output by the host computer and outputs a PWM signal with the corresponding duty cycle to the motor driver. The motor driver changes the output voltage according to the PWM signal, drives the DC motor to perform speed regulation and commutation, and performs speed regulation, commutation and position control on the electro-hydraulic actuator to realize three-dimensional spatial motion and positioning.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention provides master-slave collaborative control of hydraulic cylinders for the single-posture motion process of a six-degree-of-freedom motion platform. Based on the BP-nonlinear PID control strategy, it realizes the spatial motion and positioning of the six-degree-of-freedom platform without the need for trajectory planning, and the control process is simple and efficient. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the six-degree-of-freedom motion positioning platform control system based on EHA of the present invention; Figure 2 This is a schematic diagram of the overall structure of the electro-hydraulic actuator of the present invention; Figure 3 This is a flowchart illustrating the master-slave collaborative control process of the six-free motion positioning platform of the present invention. Figure 4 This is a schematic diagram of the basic process of the BP-nonlinear PID algorithm of the present invention.

[0017] Among them, 1-moving platform, 2-first pad block, 3-electro-hydraulic actuator, 4-second pad block, 5-static platform, 6-first ball joint, 7-DC motor, 8-motor driver, 9-gear pump, 10-pressure oil tank, 11-second ball joint, 12-hydraulic cylinder; Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] Example 1 This embodiment provides a six-degree-of-freedom motion positioning platform control system based on EHA, including: a six-degree-of-freedom platform based on EHA, a host computer, a microcontroller, a displacement sensor, an attitude sensor, a data acquisition card, and a motor driver; like Figure 1As shown, the six-degree-of-freedom platform based on EHA includes: a moving platform 1, a first pad 2, an electro-hydraulic actuator 3, a second pad 4, and a stationary platform 5. The moving platform 1 is connected to the electro-hydraulic actuator 3 through the first pad 2, and the electro-hydraulic actuator 3 is connected to the stationary platform 5 through the second pad 4. like Figure 2 As shown, the electro-hydraulic actuator includes: a first ball joint 6, a DC motor 7, an integrated valve block 8, a gear pump 9, a pressure oil tank 10, a second ball joint 11, and a hydraulic cylinder 12. The first ball joint and the second ball joint are located at both ends of the hydraulic cylinder. The first ball joint is connected to the moving platform through a first pad, and the second ball joint is connected to the stationary platform through a second pad. Among them, the hydraulic cylinder adopts an asymmetric hydraulic cylinder. The direction, speed and position of the hydraulic cylinder are controlled by the direction, speed and running time of the DC motor. The motor driver has two PWM signal input ports. The polarity of the output voltage can be changed according to the different PWM signal input ports. The output voltage can be changed according to the PWM duty cycle, thereby realizing the speed regulation and commutation function of the DC motor. The DC motor is directly connected to the gear pump via a coupling. The gear pump is a variable speed fixed displacement pump. The gear pump is connected to the DC motor via a coupling and is immersed in the oil in the pressure tank. By changing the speed of the DC motor, the pump displacement is changed, thereby achieving position control of the hydraulic cylinder. The integrated valve block uses a multi-channel integrated valve body to achieve oil pressure distribution; In this embodiment, the displacement sensor is located on one side of the hydraulic cylinder. During the movement of the hydraulic cylinder, the displacement sensor rod is driven to move. The displacement sensor is used to collect the displacement voltage signal of the hydraulic cylinder and the real-time length of the hydraulic cylinder, and transmit the displacement voltage signal to the data acquisition card. In this embodiment, six displacement sensors are preferred. In this embodiment, the attitude sensor is located at the center of the moving platform to detect the real-time pose of the moving platform; like Figure 3 As shown, the master-slave collaborative control process of the six-free motion positioning platform is as follows: After the target pose is input, the host computer calculates the target length of each hydraulic cylinder in the final target pose based on the inverse kinematics algorithm. Then, the active cylinder is determined, and its target length is used as the target displacement value Set_Value of the active cylinder. During the active cylinder position control process, given the real-time length of the active cylinder and the other five attitude parameters, a modified algorithm of the six-degree-of-freedom platform inverse kinematics algorithm can be used to calculate the real-time attitude of the six-degree-of-freedom platform during motion. The length of the driven cylinder calculated by the inverse kinematics algorithm is used as the target displacement value of the driven cylinder control algorithm. Then, the control quantity u is calculated by the BP-nonlinear PID algorithm and sent to the microcontroller. The microcontroller outputs a PWM signal to the corresponding motor driver at the corresponding port to control the coordinated movement of the six hydraulic cylinders, realizing the motion positioning function of the six-degree-of-freedom platform.

[0020] like Figure 4 As shown, the BP-nonlinear PID algorithm includes a positional digital PID algorithm, an anti-integral saturation algorithm, an integral separation algorithm, a variable speed integral algorithm, and a correction coefficient algorithm. When the previous control quantity u, the previous error value err_last, the target displacement value Set_Value, the current displacement value Actual_Value, and the cumulative integral value integral are input, it first determines whether the control quantity u has reached its maximum value (e.g., 100) or minimum value (-100). If so, the anti-integral saturation algorithm is used. Otherwise, it determines whether the absolute value of the difference between the target displacement value Set_Value and the current displacement value Actual_Value, |err|, exceeds the set threshold. If so, the integral separation algorithm is used. Otherwise, it determines whether the error value err is within the variable speed integral range. If so, the variable speed integral algorithm is used to calculate the integral value integral. Finally, the control quantity u is calculated using the positional PID algorithm, and it is determined whether the control quantity u is less than 0. If so, the correction coefficient algorithm is used. Otherwise, the control quantity u and the integral value integral are output, and the current error value err is assigned to err_last.

[0021] In this embodiment, the control quantity u is directly input to the microcontroller to generate a PWM signal with a corresponding duty cycle. The integral term of the PID algorithm and the error value err of the current cycle control algorithm are used in the next cycle control algorithm to calculate the control quantity u. In this embodiment, the anti-integral saturation algorithm is mainly used to avoid integral runaway due to excessive integral accumulation. This algorithm determines whether the value of the control variable at the previous moment is within the interval [u...]. min u max [Outside, that is, when the control quantity u at the previous moment...] (k-1) ≥u max At that time, the integral term only accumulates negative deviations, and the control quantity u from the previous moment... (k-1) <umin When the integral term accumulates only positive deviations; In this embodiment, the integral separation algorithm separates the integrals when the deviation exceeds a manually set threshold, meaning the integral term is not accumulated. Using the integral separation PID algorithm does not compromise the function of the integral term in eliminating steady-state error, thus enhancing system stability. In this embodiment, the variable-speed integral algorithm changes the cumulative velocity of the integral term to correspond to the magnitude of the deviation. Due to internal leakage in the hydraulic system and the "creeping" problem of the hydraulic cylinder, the control quantity is not zero, but the hydraulic cylinder does not move. Therefore, the variable-speed integral algorithm significantly improves the system's integral capability near zero control quantity by changing the accumulation rate of the integral term, enhancing the system's speed. The specific expression is as follows: ; In this embodiment, the expression for the correction coefficient algorithm is: ; in, The area of ​​the rodless cavity, Given the area of ​​the rod chamber, PID is a type of deviation control, and asymmetric cylinders have the characteristics of slow extension and rapid retraction. Therefore, the positive or negative control quantity is multiplied by a correction factor to weaken this effect. The correction factor can be determined by the ratio of the rod-side and rodless chamber areas of the hydraulic cylinder. In this embodiment, the expression for the positional digital PID algorithm is: ; The k-th output control quantity u(k) is calculated, with a value range of [-100, 100]. The control quantity u(k) is the duty cycle of the PWM control signal. When the control quantity is zero, the motor stops rotating; when it is positive, the DC motor rotates forward and the hydraulic cylinder extends; and when it is negative, the motor rotates backward. kp is the proportional coefficient, ki is the integral coefficient, kd is the derivative coefficient, k is the sampling number, k = 1, 2, 3…, and e(k) and e(k-1) are the deviation signals obtained at time k and time k-1, respectively. In this embodiment, the BP neural network is mainly used to improve the speed of PID control under different load conditions in EHA. By using the autonomous learning ability of the BP neural network to dynamically adjust the PID parameters, it replaces the human experience value and makes the parameters achieve the best control effect according to the load change. The three-layer BP neural network has a 4-5-3 structure. The input of the neurons in the input layer are the target displacement, actual displacement, deviation, and network threshold, respectively. The target displacement and actual displacement need to be normalized in advance. The output of the neurons in the output layer corresponds to the control parameters of the PID controller.

[0022] The transformation function for the hidden layer is chosen to be the positive-negative symmetric sigmoid function, which is: The transformation function for the output layer is chosen to be a non-negative sigmoid function, as follows: The system uses the square of the error as the performance index function, employs gradient descent to adjust the connection weights of the neural network, and updates the three control parameters kp, ki, and kd of the PID in real time during system operation.

[0023] Example 2 This embodiment provides a control method for a six-degree-of-freedom motion positioning platform based on EHA. The specific steps of the six-degree-of-freedom motion positioning platform based on EHA in embodiment 1 include: After the target posture is input (single posture parameter change), the length of the six hydraulic cylinders under the final target posture is calculated by the six-degree-of-freedom platform kinematics inverse solution algorithm; In this embodiment, single-posture motion refers to a platform motion process in which only one posture parameter (x,y,z,α,β,γ) changes. Find the absolute value of the difference between the target length of the hydraulic cylinder and the actual length of the current hydraulic cylinder, and designate the hydraulic cylinder with the largest absolute value (hydraulic cylinder stroke) as the driving cylinder, and the rest as driven cylinders; Among them, the target displacement of the active cylinder is the length calculated from the final target attitude, which is a fixed value during the movement; In the process of controlling the position of the active cylinder, given the real-time length of the active cylinder and the attitude parameters of the other five driven cylinders, the real-time attitude of the six-degree-of-freedom platform during motion can be calculated using a modified algorithm of the six-degree-of-freedom platform inverse kinematics algorithm. The length of the driven cylinder calculated by the kinematics inverse kinematics algorithm is used as the target displacement of the driven cylinder control algorithm. This value is dynamic and is updated once in each sampling control cycle.

[0024] For example, if the current posture is (0, 0, 450, 0, 0, 0), the outrigger length is 460.3. The final posture of the single-posture motion is (0, 0, 450, 15, 0, 0). In this posture, the lengths of each EHA cylinder are (482.2655, 511.8207, 489.2136, 431.1461, 411.2666, 439.5482). Cylinder 2 has the longest stroke and is the active cylinder; its control algorithm's target displacement is always 511.82. 07. The other cylinders are driven cylinders, and the driving cylinder extends from 460.3. In the next control cycle, the driving cylinder becomes 462. Then, based on the length of the driving cylinder 462 at this time and the other five unchanged attitude parameters (0, 0, 450, X, 0, 0), the ideal attitude at this time is calculated by inverse kinematics as (0, 0, 450, 0.2, 0, 0). Then, based on the ideal attitude, the length of each EHA cylinder in this attitude is calculated by inverse kinematics as the target displacement of the control algorithm of the other driven cylinders. This process is repeated.

[0025] In this embodiment, all six hydraulic cylinders are controlled using a BP-nonlinear PID algorithm. Since the target length input of the active cylinder is directly the length corresponding to the final target posture, when the posture changes significantly, the displacement input is also large, which can cause the active cylinder to move too fast. Excessive speed of the active cylinder can lead to an increase in system coordination error. Therefore, it is necessary to limit the maximum value (duty cycle) or the maximum speed of the control quantity u output by the control algorithm of the active cylinder. The maximum speed can be directly calculated as the real-time speed. Once the set speed is exceeded, the duty cycle is not allowed to increase further. The maximum duty cycle limit can be set so that if the duty cycle calculated by the control algorithm exceeds the maximum duty cycle, the output will be based on the maximum allowable duty cycle. If it does not exceed the maximum duty cycle, the output will be based on the original value. Through the above control strategy, the coordinated movement of the six cylinders and the single posture movement of the six-degree-of-freedom platform can be achieved.

[0026] In this embodiment, the control quantity u is sent to the host computer, which generates a control command with a corresponding duty cycle. The microcontroller receives the duty cycle control command output by the host computer and outputs a PWM signal with a corresponding duty cycle to the PWM signal input port of the motor driver. The motor driver can adjust the polarity of the output voltage according to the control interface of the PWM signal input and adjust the magnitude of the output voltage according to the PWM duty cycle, thereby controlling the speed, direction and position of the electro-hydraulic actuator, so that the moving platform can achieve three-dimensional spatial motion and positioning. In this embodiment, the microcontroller receives the data acquisition control command output by the host computer, obtains the displacement voltage signal of the data acquisition card, quantizes and analyzes it into the actual displacement value, and transmits it to the host computer. By calculating the attitude and target displacement in real time, the active cylinder and the driven cylinder achieve coordinated control, thereby reaching the target displacement of the six-free platform. In this embodiment, the microcontroller receives alarm control commands output by the host computer, and issues alarms for displacement sensor values ​​exceeding limits and platform reaching extreme positions.

[0027] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A six-degree-of-freedom motion positioning platform control system based on EHA, characterized in that, include: The system consists of an EHA-based six-degree-of-freedom platform, a host computer, a microcontroller, displacement sensors, attitude sensors, a data acquisition card, and a motor driver. The six-degree-of-freedom platform is equipped with multiple electro-hydraulic actuators, each of which includes a hydraulic cylinder and a DC motor. The motor driver is connected to the DC motor; The displacement sensor is located on one side of the hydraulic cylinder and is used to collect the displacement voltage signal of the hydraulic cylinder. The attitude sensor is used to acquire the real-time pose of the six-degree-of-freedom platform; The host computer calculates the target length of each hydraulic cylinder under the target posture based on the inverse kinematics algorithm, determines the active cylinder, and uses the target length as the target displacement value of the active cylinder. The driven cylinder length is calculated using the inverse kinematics algorithm and used as the target displacement value of the driven cylinder. The corresponding duty cycle control command is then generated. The microcontroller receives the duty cycle control command output by the host computer and outputs a PWM signal with the corresponding duty cycle to the motor driver. The motor driver changes the output voltage according to the PWM signal, drives the DC motor to perform speed regulation and commutation, and performs speed regulation, commutation and position control of the electro-hydraulic actuator to realize three-dimensional spatial motion and positioning.

2. The six-degree-of-freedom motion positioning platform control system based on EHA according to claim 1, characterized in that, The six-degree-of-freedom platform further includes: a moving platform, a first pad, a second pad, and a stationary platform. The moving platform is connected to the electro-hydraulic actuator through the first pad, and the electro-hydraulic actuator is connected to the stationary platform through the second pad.

3. The six-degree-of-freedom motion positioning platform control system based on EHA according to claim 2, characterized in that, The electro-hydraulic actuator further includes: a first ball joint, an integrated valve block, a gear pump, a pressure tank, and a second ball joint; The first ball joint and the second ball joint are located at both ends of the hydraulic cylinder. The first ball joint is connected to the moving platform through the first pad, and the second ball joint is connected to the stationary platform through the second pad. The DC motor is connected to the gear pump via a coupling. The gear pump is located in the pressure tank. The gear pump changes its displacement based on the speed of the DC motor. The flow rate discharged by the gear pump flows through the integrated valve block to the hydraulic cylinder. The stroke length of the hydraulic cylinder is adjusted based on the pump displacement.

4. The six-degree-of-freedom motion positioning platform control system based on EHA according to claim 1, characterized in that, The host computer calculates the control quantity based on the BP-nonlinear PID algorithm, which includes positional digital PID algorithm, anti-integral saturation algorithm, integral separation algorithm, variable speed integral algorithm, and correction coefficient algorithm. After inputting the previous control quantity, previous error value, target displacement value, current displacement value, and cumulative integral value, determine whether the control quantity has reached its maximum or minimum value. If so, use the anti-integral saturation algorithm; otherwise, determine whether the absolute value of the difference between the target displacement value and the current displacement value exceeds the set threshold. If so, use the integral separation algorithm; otherwise, determine whether the error value is within the variable speed integral range. If so, use the variable speed integral algorithm to calculate the integral value, calculate the control quantity using the positional PID algorithm, and determine whether the control quantity is less than 0. If so, use the correction coefficient algorithm; otherwise, output the control quantity. The PID parameters are adjusted based on the BP neural network, and the outputs of the neurons in the output layer of the BP neural network correspond to the control parameters of the PID controller.

5. The six-degree-of-freedom motion positioning platform control system based on EHA according to claim 4, characterized in that, Before calculating the integral term, the anti-integral saturation algorithm determines whether the value of the control quantity at the previous moment is within the interval [u]. min u max In addition, when the control quantity u at the previous moment (k-1) ≥u max At that time, the integral term only accumulates negative deviations, and the control quantity u from the previous moment... (k-1) min When the integral term accumulates only the positive deviation, the integral term only accumulates the positive deviation.​ 6. The six-degree-of-freedom motion positioning platform control system based on EHA according to claim 4, characterized in that, In the integral separation algorithm, when the deviation value exceeds the set threshold, the integral term is not accumulated.

7. The six-degree-of-freedom motion positioning platform control system based on EHA according to claim 4, characterized in that, In the variable-speed integral algorithm, the accumulation speed of the integral term is changed to correspond to the magnitude of the deviation.

8. The six-degree-of-freedom motion positioning platform control system based on EHA according to claim 4, characterized in that, The expression for the correction coefficient algorithm is: ； in, The area of ​​the rodless cavity, For the area of ​​the rod cavity, , These represent the values ​​before and after the correction, respectively.

9. The six-degree-of-freedom motion positioning platform control system based on EHA according to claim 4, characterized in that, The expression for the positional digital PID algorithm is: ； Where kp is the proportional coefficient, ki is the integral coefficient, kd is the differential coefficient, k is the sampling number, and e(k) and e(k-1) are the deviation signals obtained at time k and time k-1, respectively.

10. The control method for a six-degree-of-freedom motion positioning platform control system based on EHA according to any one of claims 1-9, characterized in that, Includes the following steps: After inputting the target posture, the lengths of the six hydraulic cylinders under the final target posture are calculated using the inverse kinematics algorithm of the six-degree-of-freedom platform. Find the absolute value of the difference between the target length of the hydraulic cylinder and the actual length of the current hydraulic cylinder, and designate the hydraulic cylinder with the largest absolute value as the driving cylinder, and the rest as driven cylinders; The target displacement of the active cylinder is the length calculated from the final target attitude; The real-time attitude of the six-degree-of-freedom platform during motion is calculated using a modified version of the inverse kinematics algorithm. The length of the driven cylinder calculated by the inverse kinematics algorithm is used as the target displacement of the driven cylinder. The maximum value of the control quantity output by the control algorithm of the active cylinder or the maximum speed is limited; The host computer generates corresponding duty cycle control commands based on the control quantities. The microcontroller receives the duty cycle control commands output by the host computer and outputs a PWM signal with the corresponding duty cycle to the motor driver. The motor driver changes the output voltage according to the PWM signal, drives the DC motor to perform speed regulation and commutation, and performs speed regulation, commutation and position control on the electro-hydraulic actuator to realize three-dimensional spatial motion and positioning.

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