Feedback linearization hydraulic actuator force servo anti-disturbance control method

Abstract

The invention discloses a feedback linearization hydraulic actuator force servo anti-disturbance control method, which comprises the following steps of: 1, establishing a complete nonlinear force servo system model by determining key parameters of a hydraulic quadruped robot actuator; step 2, converting the nonlinear model into a linear form based on a single-input single-output feedback linearization thought, and designing a final nominal control law in combination with a sliding mode control thought; and step 3, designing a Lyapunov function, theoretically proving the stability of the closed-loop system, establishing a simulation model in simulation software, and performing simulation verification on the effectiveness of the control law. The control law has anti-disturbance robustness, and the compensation nonlinear part is combined, so that the hydraulic actuator force servo tracking dynamic performance and tracking precision are improved.

Description

Technical Field

[0001] This invention belongs to the field of servo control and motion modeling of hydraulic quadruped robots, and specifically relates to a feedback linearized hydraulic actuator force servo anti-disturbance control method. Background Technology

[0002] Quadruped robots, a hot topic in biomimetic robotics research, demonstrate strong adaptability in various complex and unstructured working environments due to their high dynamic flexibility and stability under discontinuous support. This has led to a surge in demand for quadruped robots in numerous fields and scenarios, particularly in harsh environments such as field exploration, earthquake rescue, and border patrol. Compared to electric and pneumatic drives, hydraulic drives offer higher dynamic performance, greater load capacity, and stronger anti-interference capabilities. However, traditional hydraulic position servo control cannot meet the requirement of smooth interaction between the robot and its environment during movement, resulting in poor stability during actual operation. Addressing these issues necessitates high-precision force servo capabilities in hydraulic actuators.

[0003] In existing technologies, hydraulic servo control mainly focuses on using model-independent PID control to track the output force of the hydraulic cylinder. Patent CN112460095A only uses the error between the actual output force and the expected output force to generate the servo valve control current. This PID parameter is only applicable to a certain working point. However, the output force and output displacement of the hydraulic actuators on legged robots vary widely and frequently, resulting in poor force servo accuracy outside the working point range. Another control approach is to use intelligent methods such as reinforcement learning to complete the nonlinear model for control. Patent CN114953510A uses an intelligent control method to achieve optimal coordinated control of the hydraulic cylinder's motion and output force. However, intelligent control is highly dependent on all working condition data, making it difficult to transfer to practical engineering applications. Summary of the Invention

[0004] To address the problem of high-precision force servo control for hydraulic actuators in hydraulic quadruped robots, this invention proposes an anti-disturbance sliding mode control method based on the concept of feedback linearization.

[0005] The technical solution to achieve the purpose of this invention is as follows:

[0006] A feedback linearized force servo disturbance rejection control method for hydraulic actuators, with the following control law:

[0007] ;

[0008] in For the desired servo valve control current, k is the derivative of the desired output force. s and q s For control coefficients, The piston area of ​​the rodless chamber of the hydraulic cylinder. This refers to the piston area of ​​the rod chamber in a hydraulic cylinder. The effective bulk modulus of hydraulic oil. Where L is the displacement of the hydraulic cylinder piston, and K is the stroke of the hydraulic cylinder piston. v For gain, This represents the actual servo valve current. For oil supply pressure, The pressure in the rodless chamber of the hydraulic cylinder. For the rod chamber pressure of the hydraulic cylinder, For the designed sliding surface, sign(s) and sign(I) are both sign functions, where:

[0009] ; .

[0010] The significant advantages of this invention compared to existing technologies are:

[0011] Based on the structural characteristics of the hydraulic quadruped robot drive unit, this invention establishes a complete nonlinear system model of hydraulic actuator force servo and designs a sliding mode control law based on feedback linearization. The control law has robustness against disturbances, and the combination of compensation nonlinear part improves the dynamic performance and tracking accuracy of hydraulic actuator force servo tracking, which can effectively improve the motion stability of hydraulic quadruped robots. Attached Figure Description

[0012] Figure 1 Schematic diagram of an asymmetric cylinder controlled by a zero-opening four-way slide valve.

[0013] Figure 2 This is a schematic diagram of a force servo control system for a hydraulic actuator.

[0014] Figure 3 This is a schematic diagram of a hydraulic actuator force servo system tracking the desired force. Detailed Implementation

[0015] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0016] The present invention provides a feedback linearized force servo anti-disturbance control method for hydraulic actuators, comprising the following steps:

[0017] 1. By determining the key parameters of the hydraulic quadruped robot actuator, a complete nonlinear force servo system model is established. The specific steps are as follows:

[0018] First, a nonlinear force servo system model of the corresponding hydraulic actuator is established based on the direction of the operating force output from the input control current signal to the actuator. (Refer to...) Figure 1As shown, the actuator employs the principle of a zero-opening four-way spool valve controlling an asymmetric hydraulic cylinder. The control algorithm on the drive controller generates a control current and sends it to the servo valve. The servo valve controls the valve core displacement based on the input current. The valve core displacement signal directly affects the flow rate into / out of the two chambers of the asymmetric hydraulic cylinder, ultimately determining the pressure change in both chambers. (Servo valve core displacement) With servo valve current The relationship is

[0019]

[0020] in, For the servo valve spool displacement-current gain ( ); For the servo valve's natural frequency ( ); For servo valve damping ratio; For valve core displacement ( ); Valve core speed ( ); Valve core acceleration ( The natural frequency of a servo valve is strongly correlated with its hardware structure design, but it is much higher than the 2Hz motion frequency commonly found in hydraulic quadruped robots. Furthermore, most servo valve products lack a spool displacement sensor. Therefore, the following relationship is used to approximate the servo valve spool displacement. ( ) and servo valve current ( The relationship between )

[0021]

[0022] Further establishing the flow equation for the servo valve, the servo valve spool displacement and the pressure difference across the servo valve orifice jointly determine the flow direction and magnitude. That is, the servo valve spool displacement and pressure difference are the input signals, and the flow rate through the servo valve orifice... ( )for

[0023]

[0024] in, For the servo valve slide valve throttle port flow coefficient; The gradient of the throttling orifice area of ​​the slide valve ( ); The density of hydraulic oil ( ); Let be the pressure difference at the spool valve orifice. Since the servo valve orifice flow coefficient, spool valve area gradient, and hydraulic oil density are inherent values ​​for a given hydraulic actuator, a gain is defined for ease of subsequent expression.

[0025]

[0026] The expression for the inlet flow rate is then obtained as follows:

[0027]

[0028] in, For oil supply pressure ( ); For the rodless chamber pressure of the hydraulic cylinder ( ); For the oil inlet flow rate ( Since the sign of the input current to the servo valve indicates its direction, that is, the direction of movement of the servo valve, the positive / negative sign of this flow rate expression can be considered as the magnitude of the flow rate flowing into / out of the rodless chamber of the hydraulic cylinder. To simplify the expression, the above formula is further simplified to...

[0029]

[0030] Among them, the sign function Meanwhile, the expression for the oil outlet flow rate is:

[0031]

[0032] in, Oil outlet flow rate ( ); For the rod chamber pressure of the hydraulic cylinder ( The above formula can also be simplified to:

[0033]

[0034] Further, an asymmetric hydraulic cylinder model is established. During analysis, it's important to note that the two chambers of the asymmetric hydraulic cylinder have different areas. Therefore, the flow rates into / out of the two chambers at the same velocity are different, but the required instantaneous flow rate is smaller. Furthermore, it is assumed that the pressure in each chamber of the hydraulic cylinder is the same everywhere, and leakage is ignored. Then, from the continuity equation of the hydraulic cylinder, we have:

[0035]

[0036] in, The derivative of pressure in a rodless cavity ( ); The derivative of pressure in the rod cavity ( ); The effective bulk modulus of hydraulic oil (Pa); The volume of the rodless chamber of the hydraulic cylinder ( ); The volume of the rod chamber of the hydraulic cylinder ( ); The piston area of ​​the rodless chamber of the hydraulic cylinder ( ); The piston area of ​​the rod chamber of the hydraulic cylinder ( ); The displacement of the hydraulic cylinder piston (m); For the piston speed of the hydraulic cylinder ( ).

[0037] Furthermore, the output force of the hydraulic actuator is obtained based on the pressure in both chambers of the hydraulic cylinder. ( )for

[0038]

[0039] 2. Based on the single-input single-output feedback linearization concept, the above nonlinear model is transformed into a linear form. Then, combined with the sliding mode control concept, the final nominal control law is designed. The complete hydraulic actuator force servo control system structure is as follows: Figure 2 As shown, the specific steps are as follows:

[0040] First, the hydraulic actuator force servo system model established in step 1, which focuses on control and transforms input control current into output force, is summarized as follows:

[0041]

[0042] As can be seen from the complete nonlinear model of the hydraulic actuator force servo above, the input control current signal first affects the displacement of the servo valve slide valve, further changes the flow rate into and out of the two chambers of the hydraulic cylinder, then affects the pressure in the two chambers of the hydraulic cylinder and the piston movement, and finally determines the output force of the hydraulic cylinder.

[0043] Then, based on the single-input single-output feedback linearization concept, the control current explicitly expresses the hydraulic cylinder output force by deriving the equation of the hydraulic cylinder output force from the hydraulic cylinder output force equation. First, the derivative of the hydraulic cylinder output force is obtained...

[0044]

[0045] in, This is the derivative of the hydraulic cylinder's output force. Substituting the derivatives of the pressures in the two chambers of the hydraulic cylinder into the above equation, we get...

[0046]

[0047] Assume the piston stroke of the hydraulic cylinder is L ( Given the length of the rodless chamber of the hydraulic cylinder and the displacement of the hydraulic cylinder piston. If equivalent, the above equation can be written as

[0048]

[0049] Further substituting the flow equation into the...

[0050]

[0051] The above formula shows the explicit relationship between the output force derivative of the hydraulic actuator and the control current of the servo valve.

[0052] Next, we can transform the above equation, assuming there exists an ideal servo valve control current. ( This makes the hydraulic drive unit force servo closed-loop system become

[0053]

[0054] in, ; For the designed sliding surface; For the ideal hydraulic cylinder output force ( ); Derivatives of the designed sliding surface; sign function ; and If is the control coefficient, then the final actual control law is:

[0055]

[0056] in, This is the derivative of the desired output force.

[0057] 3. Design a Lyapunov function, theoretically prove the stability of the closed-loop system, and build a simulation model to verify the effectiveness of the above control law. The specific steps are as follows:

[0058] First, analyzing the hydraulic actuator force servo closed-loop system using the aforementioned control law requires considering whether the denominator of the control law can be zero. If the denominator is zero, it will lead to calculation divergence and errors in practical engineering applications. Furthermore, constraints exist from the perspective of the actual physical system.

[0059]

[0060] As can be seen from the above constraints, the denominator in the above control law will never be equal to zero, therefore the control law has practical engineering significance.

[0061] Next, the stability of the hydraulic actuator force servo closed-loop system is analyzed. First, the Lyapunov function is defined. Differentiating it has

[0062]

[0063] As can be seen from the above formula, when there is an error between the actual output force and the desired force of the hydraulic actuator, the control law will always make the actual output force move in the direction of reducing the error until the error is zero. This shows that under the control law, the hydraulic actuator force servo closed-loop system is always asymptotically stable.

[0064] To weaken the control law mentioned above The system chattering problem arises from a sudden change at the zero crossing, which can lead to system chattering issues. The aforementioned control law... Replace with a continuously varying hyperbolic tangent function The specific expression for the hyperbolic tangent function is as follows:

[0065]

[0066] in, is the base of the natural logarithm.

[0067] Finally, a nonlinear simulation model of the hydraulic actuator force servo was built. The load was set as an inertial load in the simulation. However, for the force servo system, the piston is rigidly connected to the load, meaning the piston's speed is the same as the load's speed. Therefore, this force servo system operates under displacement disturbance, tracking the output force. The desired output force is set as... The piston's speed is ,in For simulation time ( Then, the actual output force tracking of the hydraulic actuator is as follows: Figure 3 As shown in the figure. The simulation results show that under this control law, the force tracking error of the force servo closed-loop system is 5.5%, and the phase lag is 21.6°.

Claims

1. A feedback linearized hydraulic actuator force servo disturbance control method, characterized by, The control law thereof is: ； wherein is the desired servo valve control current, is the derivative of the desired output force, k s and q s is a control coefficient, is the hydraulic cylinder rodless chamber piston area, is the hydraulic cylinder rodded chamber piston area, is the hydraulic oil effective volume modulus of elasticity, is the hydraulic cylinder piston displacement, L is the hydraulic cylinder piston stroke, K v is the gain, is the actual servo valve current, is the supply oil pressure, is the hydraulic cylinder rodless chamber pressure, is the hydraulic cylinder rodded chamber pressure, is the designed sliding mode surface, sign(s), sign(I) are sign functions, wherein: ； 。 2. The feedback linearized hydraulic actuator force servo anti-disturbance control method according to claim 1, characterized by, Slip surface Is: ； ； wherein is the output force of the hydraulic actuator, is the desired hydraulic cylinder output force.

3. The feedback linearized hydraulic actuator force servo anti-disturbance control method according to claim 1, characterized by, Gain K v is: ； wherein, Ksv is the spool valve spool orifice flow coefficient, Ksv is the spool valve spool orifice flow coefficient, Ksv is the spool valve spool orifice flow coefficient, 4. The feedback linearized hydraulic actuator force servo disturbance control method according to claim 1 or 2, characterized by, The pressure of the rodless cavity of the hydraulic cylinder and the pressure of the rod cavity satisfy: ； wherein is the rodless chamber pressure derivative, is the rod chamber pressure derivative, is the hydraulic cylinder rodless chamber volume, is the hydraulic cylinder rod chamber volume, is the oil inlet flow, is the oil outlet flow, is the hydraulic cylinder piston velocity.

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