A control method for electrostatic hydraulic actuator with leakage compensation

Abstract

The present application relates to a control method for an electrostatic hydraulic actuator with leakage compensation, which realizes control of an EHA system through a pressure difference controller and a current controller, and includes the following steps: inputting a pressure difference instruction, the pressure difference instruction includes an expected pressure difference, the pressure difference controller calculates an expected current, the current controller outputs a voltage signal to a motor driver according to the expected current, the motor driver drives the EHA motor to actuate, the expected pressure difference is calculated by a feedforward part to obtain a feedforward expected current, the expected pressure difference is subtracted from the actual pressure difference to obtain a pressure difference error, a PD controller calculates a feedback expected current, the motor speed required for leakage compensation is calculated by the actual pressure difference, the motor speed is subtracted from the actual motor speed to obtain a speed error, and the speed error is used to obtain a leakage compensation expected current through a PID controller. The control method for an electrostatic hydraulic actuator has a faster response speed and a better pressure-maintaining effect.

Description

Technical Field

[0001] The present application relates to the technical field of electrostatic hydraulic actuators, and in particular to a control method of an electrostatic hydraulic actuator with leakage compensation. Background Art

[0002] Electrostatic hydraulic actuator (EHA) is a commonly used hydraulic system that uses advanced hydraulic components and control devices to achieve high-precision and high-speed motion control. When the existing electrostatic hydraulic actuator outputs steady-state force (i.e., maintains pressure), the pressure difference of the system will decrease over time due to leakage of the pump and hydraulic cylinder. Therefore, during the process of maintaining pressure, the motor needs to rotate to generate flow to compensate for the leakage flow, thereby maintaining a stable pressure difference.

[0003] At present, the force control of the electrostatic hydraulic actuator mainly adopts the control strategy of pressure difference-speed-current loop. A speed loop is added between the pressure difference loop and the current loop to control the pressure difference, and the speed loop is used to compensate for leakage. However, the control strategy of pressure difference-speed-current loop will slow down the force control response of the system because a speed loop is added between the pressure difference-current loop.

[0004] Some existing nonlinear force control methods, such as robust control and adaptive control, are easy to implement in simulation, but have many inconveniences in actual use. First, they are limited by the limited computing power of the controller, and second, the parameter debugging is complicated. Therefore, PID controllers are still the main controllers in actual use. However, the existing pressure-current loop PID control strategy is mainly used for low-pressure conditions, with small leakage, so leakage compensation is not considered. However, the EHA leakage increases at high pressure, so the existing PID control strategy is not suitable for high-pressure conditions. Summary of the invention

[0005] The present invention aims to provide an electrostatic hydraulic actuator control method with leakage compensation to solve the deficiencies in the prior art. The method can perform leakage compensation of the pressure difference-current loop without reducing the EHA force control response speed, improve the pressure holding capacity of the EHA in a steady state, and be applicable to high and low pressure working conditions. The control strategy is simple, and the control parameters are easy to adjust and can be used in practice. The technical problem to be solved by the present invention is achieved by the following technical solutions.

[0006] A control method for an electrostatic hydraulic actuator with leakage compensation realizes control of an EHA system through a pressure difference controller and a current controller, and specifically comprises the following steps:

[0007] S1: Input the pressure difference instruction, which includes the set expected pressure difference;

[0008] S2: The pressure difference controller calculates the desired current;

[0009] S3: The current controller outputs a voltage signal to the motor driver according to the desired current;

[0010] S4: The motor driver drives the EHA motor to actuate;

[0011] The pressure difference controller consists of three parts, namely the feedforward part, the PD controller and the leakage compensation part, where S2 includes the following steps:

[0012] S21: The expected voltage difference is calculated by the feedforward part to obtain the feedforward expected current i ff ;

[0013] S22: The expected pressure difference is subtracted from the actual pressure difference to obtain the pressure difference error. The pressure difference error is calculated by the PD controller to obtain the feedback expected current. i PD ;

[0014] S23: The leakage compensation part calculates the motor speed required for leakage compensation through the actual pressure difference. The speed error is obtained by subtracting the motor speed from the actual motor speed. The speed error is used to obtain the leakage compensation expected current through the PID controller. i ed ;

[0015] S24: Feedforward desired current i ff , Feedback expected current i PD , leakage compensation expected current i ed The three are added together to get the desired current.

[0016] Preferably, S3 comprises the following steps:

[0017] S31: Subtract the expected current from the actual motor current fed back by the EHA system to obtain a current error;

[0018] S32: The PID controller converts the current error into a voltage signal and outputs it to the motor driver.

[0019] Preferably, the actual pressure difference is collected by the pressure sensors of the two chambers of the EHA system and obtained by subtracting them, the actual current of the motor is collected by the driver of the EHA system, and the actual speed of the motor is collected by the encoder of the EHA system.

[0020] Preferably, the feed-forward desired current i ff Calculated by the following method:

[0021] First, the kinetic equation of the EHA system is established.

[0022] Motor Driven Piston Pump Model:

[0023]

[0024] Piston pump driven hydraulic cylinder model:

[0025]

[0026] Hydraulic cylinder drive load model:

[0027]

[0028] Taking the derivative of (2), we get

[0029]

[0030] Substituting equations (1) and (3) into equation (4), we can obtain

[0031]

[0032] in, x is the displacement of the piston rod, m is the piston rod mass, Δ P is the pressure difference between the two chambers of the hydraulic cylinder, A is the effective area of ​​the piston rod, F l is the load force, ω is the motor speed, J is the motor pump moment of inertia, K is the torque constant of the motor, is the motor current, D p is the pump displacement, E is the elastic modulus of the hydraulic oil, V is the volume of the hydraulic cylinder, C ed is the leakage coefficient of the hydraulic cylinder, F f is the friction damping force of the hydraulic cylinder, B m is the viscous damping coefficient of the micro plunger pump, B c is the damping coefficient of the hydraulic cylinder, K f is the friction coefficient of the hydraulic cylinder.

[0033] From formula (5), we can get the feedforward expected current i ff for:

[0034]

[0035] Preferably, the feedback desired current i PD Calculated by the following method:

[0036]

[0037] Where ΔP act is the actual pressure difference, K p , K d are the control parameters of the proportional term and the differential term in the PD controller respectively.

[0038] Preferably, the leakage compensation desired current i ed Calculated by the following method:

[0039] From formula (2), we can know that the motor speed required to compensate for leakage is:

[0040]

[0041] In the formula, K ep , K ei , K ed They are the control parameters of the proportional term, integral term and differential term in the PID controller of the leakage compensation part.

[0042] Preferably, the desired current is , defining the current error , i act is the actual motor current, and the voltage of the PID in the current controller is calculated by the following method:

[0043]

[0044] In the formula, K ip , K ii , K id They are the control parameters of the proportional term, integral term and differential term in the current loop PID controller respectively.

[0045] The control method of the electrostatic hydraulic actuator with leakage compensation of the present invention has the following beneficial effects:

[0046] 1. Compared with the pressure difference-speed-current loop method in the prior art, the response speed is improved when the method of the present application is adopted.

[0047] 2. Due to the addition of leakage compensation, the pressure holding performance is improved by using the method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a block diagram of the EHA force control strategy in the prior art;

[0049] Figure 2It is a pressure difference step curve using a pressure difference-speed-current loop control strategy in the prior art;

[0050] Figure 3 is the step response time of the pressure difference-speed-current loop control strategy adopted in the prior art;

[0051] Figure 4 This is a block diagram of the pressure difference-current loop control strategy of the present invention;

[0052] Figure 5 It is the pressure difference step curve of the pressure difference-current loop when no compensation is added in the present invention;

[0053] Figure 6 This is the error curve of the voltage difference-current loop in steady state when no compensation is added in the present invention;

[0054] Figure 7 The pressure difference step curve of the pressure difference-current loop when the compensation is added in the present invention;

[0055] Figure 8 The step response time of the voltage difference-current loop when the present invention is compensated;

[0056] Fig. 9 This is the error curve of the differential pressure-current loop in steady state when the compensation is added in the present invention. DETAILED DESCRIPTION

[0057] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments.

[0058] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0059] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0061] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are directions or positional relationships in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0062] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "setting", "installation" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0063] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0064] like Figure 4 As shown, the EHA system is controlled by a pressure difference controller and a current controller. The pressure difference-current control strategy of the present invention is composed of a pressure difference controller, a current controller and an EHA system. After the pressure difference instruction is input, the desired current is calculated by the pressure difference controller, and the desired current is given to the motor driver through the output voltage signal of the current controller, and the motor driver drives the EHA motor to actuate. Specifically, the following steps are included:

[0065] S1: Input the pressure difference instruction, which includes the set expected pressure difference;

[0066] S2: The pressure difference controller calculates the desired current;

[0067] S3: The current controller outputs a voltage signal to the motor driver according to the desired current;

[0068] S4: The motor driver drives the EHA motor to actuate;

[0069] The pressure difference controller consists of three parts, namely the feedforward part, the PD controller and the leakage compensation part, where S2 includes the following steps:

[0070] S21: The expected voltage difference is calculated by the feedforward part to obtain the feedforward expected current i ff ;

[0071] S22: The expected pressure difference is subtracted from the actual pressure difference to obtain the pressure difference error. The pressure difference error is calculated by the PD controller to obtain the feedback expected current. iPD ;

[0072] S23: The leakage compensation part calculates the motor speed required for leakage compensation through the actual pressure difference. The speed error is obtained by subtracting the motor speed from the actual motor speed. The speed error is used to obtain the leakage compensation expected current through the PID controller. i ed ;

[0073] S24: Feedforward desired current i ff , Feedback expected current i PD , leakage compensation expected current i ed The three are added together to get the desired current.

[0074] Furthermore, S3 includes the following steps:

[0075] S31: Subtract the expected current from the actual motor current fed back by the EHA system to obtain a current error;

[0076] S32: The PID controller converts the current error into a voltage signal and outputs it to the motor driver.

[0077] Furthermore, the actual pressure difference is collected by the pressure sensors of the two chambers of the EHA system and obtained by subtracting them, the actual current of the motor is collected by the driver of the EHA system, and the actual speed of the motor is collected by the encoder of the EHA system.

[0078] Furthermore, the feedforward desired current i ff Calculated by the following method:

[0079] First, the kinetic equation of the EHA system is established.

[0080] Motor Driven Piston Pump Model:

[0081]

[0082] Piston pump driven hydraulic cylinder model:

[0083]

[0084] Hydraulic cylinder drive load model:

[0085]

[0086] Taking the derivative of (2), we get

[0087]

[0088] Substituting equations (1) and (3) into equation (4), we can obtain

[0089]

[0090] in, x is the displacement of the piston rod, m is the piston rod mass, Δ P is the pressure difference between the two chambers of the hydraulic cylinder, A is the effective area of ​​the piston rod, F l is the load force, ω is the motor speed, J is the motor pump moment of inertia, K is the torque constant of the motor, is the motor current, D p is the pump displacement, E is the elastic modulus of the hydraulic oil, V is the volume of the hydraulic cylinder, C ed is the leakage coefficient of the hydraulic cylinder, F f is the friction damping force of the hydraulic cylinder, B m is the viscous damping coefficient of the micro plunger pump, B c is the damping coefficient of the hydraulic cylinder, K f is the friction coefficient of the hydraulic cylinder.

[0091] From formula (5), we can get the feedforward expected current i ff for:

[0092] .

[0093] Furthermore, the feedback desired current is i PD It is calculated by the following method:

[0094]

[0095] Where ΔP act is the actual pressure difference, K p , K d are the control parameters of the proportional term and the differential term in the PD controller respectively.

[0096] Furthermore, the leakage compensation expected current i ed Calculated by the following method:

[0097] From formula (2), we can know that the motor speed required to compensate for leakage is:

[0098]

[0099] In the formula, K ep , K ei , K ed They are the control parameters of the proportional term, integral term and differential term in the PID controller of the leakage compensation part.

[0100] Furthermore, the expected current is , defining the current error ,i act is the actual motor current, and the voltage of the PID in the current controller is calculated by the following method:

[0101]

[0102] In the formula, K ip , K ii , K id They are the control parameters of the proportional term, integral term and differential term in the current loop PID controller respectively.

[0103] It should be noted that the above detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present application belongs.

[0104] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments described in the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0105] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0106] In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or inherent to these processes, methods, products, or apparatuses.

[0107] For ease of description, spatially relative terms, such as "above", "above", "on the upper surface of", "above", etc., may be used herein to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" may include both "above" and "below". The device may also be positioned in other different ways, such as rotated 90 degrees or in other orientations, and the spatially relative descriptions used herein are interpreted accordingly.

[0108] In the above detailed description, reference is made to the accompanying drawings, which form a part of this document. In the accompanying drawings, similar symbols typically identify similar components unless the context indicates otherwise. The illustrated embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be used, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein.

[0109] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A control method for an electrostatic hydraulic actuator with leakage compensation, characterized in that: The control of the EHA system is achieved through a pressure difference controller and a current controller, which specifically includes the following steps: S1: Input the pressure difference instruction, which includes the set expected pressure difference; S2: The pressure difference controller calculates the desired current; S3: The current controller outputs a voltage signal to the motor driver according to the desired current; S4: The motor driver drives the EHA motor to actuate; The pressure difference controller consists of three parts, namely the feedforward part, the PD controller and the leakage compensation part, where S2 includes the following steps: S21: The expected voltage difference is calculated by the feedforward part to obtain the feedforward expected current i ff ; S22: The expected pressure difference is subtracted from the actual pressure difference to obtain the pressure difference error. The pressure difference error is calculated by the PD controller to obtain the feedback expected current. i PD ; S23: The leakage compensation part calculates the motor speed required for leakage compensation through the actual pressure difference. The speed error is obtained by subtracting the motor speed from the actual motor speed. The speed error is used to obtain the leakage compensation expected current through the PID controller. i ed ; S24: Feedforward desired current i ff , Feedback expected current i PD , leakage compensation expected current i ed The three are added together to get the desired current; S3 includes the following steps: S31: Subtract the expected current from the actual motor current fed back by the EHA system to obtain a current error; S32: The PID controller converts the current error into a voltage signal and outputs it to the motor driver; Feedforward desired current i ff Calculated by the following method: First, the kinetic equation of the EHA system is established. Motor driven piston pump model: Piston pump driven hydraulic cylinder model: Hydraulic cylinder drive load model: Taking the derivative of (2), we get: Substituting equations (1) and (3) into equation (4), we can obtain: in, x is the displacement of the piston rod, m is the piston rod mass, Δ P is the pressure difference between the two chambers of the hydraulic cylinder, A is the effective area of ​​the piston rod, F l is the load force, ω is the motor speed, J is the motor pump moment of inertia, K is the torque constant of the motor, is the motor current, D p is the pump displacement, E is the elastic modulus of the hydraulic oil, V is the volume of the hydraulic cylinder, C ed is the leakage coefficient of the hydraulic cylinder, F f is the friction damping force of the hydraulic cylinder, B m is the viscous damping coefficient of the micro plunger pump, B c is the damping coefficient of the hydraulic cylinder, K f is the friction coefficient of the hydraulic cylinder; From formula (5), we can get the feedforward expected current i ff for: ； Feedback desired current i PD Calculated by the following method: In the formula, ΔP act is the actual pressure difference, K p , K d are the control parameters of the proportional term and the differential term in the PD controller respectively; Leakage compensation expected current i ed Calculated by the following method: From formula (2), we can know that the motor speed required to compensate for leakage is: In the formula, K ep , K ei , K ed They are the control parameters of the proportional term, integral term and differential term in the PID controller of the leakage compensation part respectively.

2. The control method of an electrostatic hydraulic actuator with leakage compensation according to claim 1, characterized in that: The actual pressure difference is collected by the pressure sensors of the two chambers of the EHA system and obtained by subtracting them. The actual current of the motor is collected by the driver of the EHA system, and the actual speed of the motor is collected by the encoder of the EHA system.

3. The control method of an electrostatic hydraulic actuator with leakage compensation according to claim 1, characterized in that: The expected current is , defining the current error , i act is the actual motor current, and the voltage of the PID in the current controller is calculated by the following method: In the formula, K ip , K ii , K id They are the control parameters of the proportional term, integral term and differential term in the current loop PID controller respectively.

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