Accurate displacement acquisition method for nonlinear control system of valve-controlled swing hydraulic motor based on experiment identification and implementation system of accurate displacement acquisition method

Abstract

The invention relates to the technical field of hydraulic transmission and control, in particular to a method for accurately acquiring the displacement of a nonlinear control system of a valve-controlled swing hydraulic motor based on experimental identification and an implementation system thereof. According to the method, before a nonlinear control system of the valve-controlled swing hydraulic motor formally enters closed-loop control, displacement parameters of the valve-controlled swing hydraulic motor are accurately obtained in an open-loop state through an experiment identification means under the condition that no additional sensor is added, and the obtained accurate displacement is used for designing a nonlinear control law based on a model, so that the accuracy of the valve-controlled swing hydraulic motor is improved. And designing a closed-loop control system. According to the method, the problem that the control precision is reduced due to uncertain displacement can be effectively solved, meanwhile, the parameter convergence time and the continuous excitation condition needed by a parameter self-adaption method are avoided, the transient state and steady state control precision is ensured, and the control precision and stability of the system are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of hydraulic transmission and control technology, and in particular to a method for accurately obtaining the displacement of a nonlinear control system of a valve-controlled swing hydraulic motor based on experimental identification and an implementation system thereof. The present invention uses experimental identification means to accurately obtain the displacement parameters of a valve-controlled swing hydraulic motor without adding additional sensors, thereby significantly improving the accuracy and stability of the control system. Background Art

[0002] The valve-controlled swing hydraulic motor, also known as the swing hydraulic cylinder, is a special hydraulic actuator whose output shaft can perform reciprocating swing (rather than continuous rotation) motion. This type of motor plays an important role in hydraulic systems, especially in situations where limited rotational motion and high torque are required. Valve-controlled swing hydraulic motor control systems are widely used in special robots, port machinery, aerospace and other fields due to their advantages such as high power density, fast dynamic response, and small installation space. However, in order to achieve high-precision control of valve-controlled hydraulic motors, in addition to overcoming the inherent pressure-flow nonlinearity of the servo valve, it is also necessary to solve the parameter uncertainty and uncertain nonlinearity problems existing in the entire system. Obviously, linear control methods such as PID cannot cope with the above problems well, while model-based nonlinear control methods have natural advantages.

[0003] The displacement of the nonlinear control system of the valve-controlled hydraulic motor is a key parameter and plays an important role in the design process of the nonlinear control method. It is used to calculate variables such as load flow, output torque, and control volume. For angle and torque control systems, especially for large-amplitude and high-speed motion conditions, it is critical to obtain the precise displacement of the motor. However, when faced with some situations where the theoretical design displacement cannot be obtained, such as some renovation projects, the displacement parameters will be unknown. At present, it is a common processing method to regard the motor displacement as a parameter uncertainty and perform adaptive estimation. The motor displacement is estimated by the parameter adaptive method, and then used in the design of the nonlinear control method of the valve-controlled swing hydraulic motor control system. This method has the following main defects:

[0004] 1. When the motor displacement is completely unknown and there is no setting criteria for the parameter adaptation rate, the unreasonable displacement convergence speed will limit the transient control accuracy of the valve-controlled swing hydraulic motor control system. In addition, the parameter adaptation method also needs to meet the continuous excitation conditions, which also limits the promotion and application of the above method.

[0005] 2. Existing research methods cannot handle changes in the control volume of the swing hydraulic motor. Through parameter adaptation and when the continuous excitation conditions are met, the motor displacement in the steady state can usually be obtained. However, due to changes in the position of the motor, the control volume also changes accordingly. If this method is applied, in the design process of the nonlinear control method, the motor displacement used to calculate the real-time control volume is not obtained through the parameter adaptation method, but a nominal value is substituted or directly ignored, resulting in inaccuracy in the design process of the nonlinear control method. Especially when the hydraulic motor moves greatly, the change in control volume is more drastic, resulting in a large change in the model parameters. If the precise value of the motor displacement cannot be obtained, the control accuracy will be greatly reduced. In addition, the existing parameter adaptation method needs to meet the excitation conditions, which is also a limiting factor in practical applications.

[0006] Therefore, it is necessary to explore a new method to obtain more accurate motor displacement and improve control accuracy.

[0007] It should be noted that the information disclosed in this background technology section is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or suggestion in any form that the information constitutes the prior art known to those skilled in the art. Summary of the invention

[0008] The purpose of the present invention is to provide a method for accurately obtaining the displacement of a nonlinear control system of a valve-controlled swing hydraulic motor based on experimental identification and its implementation system. The method can accurately identify the motor displacement by experimental means before the system officially enters closed-loop control, thereby overcoming the problem of decreased control accuracy caused by uncertainty in displacement and improving the control accuracy and stability of the system.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a method for accurately obtaining the displacement of a nonlinear control system of a valve-controlled swing hydraulic motor based on experimental identification, comprising the following steps:

[0011] S1 system construction: construct an experimental platform including hydraulic power source, servo valve, acquisition element, valve-controlled swing hydraulic motor and controller;

[0012] S2 displacement identification:

[0013] S21 Experimental setup: Under open-loop control, set the pressure of the hydraulic power source to a preset value and start the controller;

[0014] S22 data acquisition: by controlling the input signal of the servo valve, the valve-controlled swing hydraulic motor generates a measurable motion or torque change; under the action of the servo valve input signal, the output data of the valve-controlled swing hydraulic motor is collected in real time through the acquisition element;

[0015] S23 data processing: according to the collected data, combined with the rated flow or load pressure of the servo valve, the precise displacement of the hydraulic motor is obtained by calculation;

[0016] S3 nonlinear control method design: The precise displacement obtained by S2 identification is used to design a model-based nonlinear control law to design a closed-loop control system.

[0017] In a second aspect, the present invention provides a valve-controlled swing hydraulic motor nonlinear control system, comprising: a hydraulic power source, a servo valve, a swing hydraulic motor, a collection element, and a controller implemented according to the method of the first aspect above, wherein the controller uses the precise displacement obtained by experimental identification to design and execute a nonlinear control strategy.

[0018] The beneficial effects of the present invention are:

[0019] 1. High-precision control: The precise value of motor displacement obtained through experimental identification can more accurately calculate variables such as load flow, output torque and control volume, thereby achieving higher control accuracy when designing nonlinear control methods.

[0020] 2. No additional components are required: Whether it is an angle control system or a torque control system, only the original encoder or torque sensor is needed to complete the displacement identification, without adding additional measuring components, reducing system complexity and cost.

[0021] 3. Avoid the limitations of parameter adaptation: Traditional parameter adaptation methods need to meet continuous excitation conditions, and the displacement convergence speed may be unreasonable, affecting the transient control accuracy. This method performs displacement identification in an open-loop state to avoid these problems.

[0022] 4. Improve system stability: The precise motor displacement value makes the design of nonlinear control method more rigorous, which can better cope with the changes of system parameters and uncertain nonlinear problems, and improve the overall stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 According to an embodiment of the present application, a control system configuration diagram of a valve-controlled hydraulic swing motor is shown;

[0024] Figure 2 According to the first embodiment of the present application, the angle and angular velocity output by the valve-controlled hydraulic swing motor angle control system are shown;

[0025] Figure 3 According to the first embodiment of the present application, the displacement identification result of the valve-controlled hydraulic swing motor angle control system is shown;

[0026] Figure 4 According to the second embodiment of the present application, the torque output by the valve-controlled hydraulic swing motor torque control system is shown;

[0027] Figure 5 According to the second embodiment of the present application, the displacement identification result of the valve-controlled hydraulic swing motor torque control system is shown;

[0028] Figure 6 According to an embodiment of the present application, a schematic diagram of a valve-controlled hydraulic swing motor nonlinear control system is shown;

[0029] Figure 7 According to the first embodiment of the present application, a result diagram of a valve-controlled hydraulic swing motor angle control system is shown;

[0030] Figure 8 According to the second embodiment of the present application, a result diagram of a valve-controlled hydraulic swing motor torque control system is shown. DETAILED DESCRIPTION

[0031] The following is a more detailed description of the technical features and advantages of the present application in conjunction with the accompanying drawings, so that the advantages and features of the present application can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0032] The embodiment of the present invention is aimed at the nonlinear control system of the valve-controlled swing hydraulic motor, including angle control and torque control, and proposes a method for accurately identifying the motor displacement through experiments in order to solve the parameter uncertainty problem of the motor displacement when designing a nonlinear control method. For the angle control system, only a unique sensor, the encoder, is required to complete the identification work; for the torque control system, only a unique sensor, the torque sensor, is required to complete the identification work. Whether it is an angle or torque control system, there is no need to add additional components to obtain the accurate motor displacement before entering the closed-loop control. Using it for the design of a nonlinear control method not only achieves high-performance closed-loop control, but also ensures the rigor of the theoretical derivation.

[0033] To achieve the above objectives, the basic idea of ​​the embodiments of the present invention is as follows: by identifying the displacement of the valve-controlled swing hydraulic motor control system under open-loop control, and then introducing the identified motor's precise displacement into the design of the nonlinear control method under closed-loop control, the model parameters of the control input and multiple intermediate variables can be accurately calculated, while avoiding the parameter convergence time and continuous excitation conditions required by the parameter adaptive method, ensuring the transient and steady-state control accuracy, and having a relatively obvious advantage.

[0034] Two specific embodiments are given below for the angle control system and the torque control system respectively.

[0035] Embodiment 1: Angle control system

[0036] 1. Experimental system construction:

[0037] (1) Design an experimental platform including a hydraulic power source, a servo valve, a swing hydraulic motor, an encoder and a controller, such as Figure 1 (a) shows that the control input range of the servo valve used is -10V to +10V, the rated flow rate is 63L / min, the number is 2, the installation form is parallel, and the zero bias correction has been completed after leaving the factory;

[0038] (2) The flow rate from the hydraulic power source to the swing hydraulic motor is regulated by the control input of the servo valve, and the control range is set to -10V to +10V.

[0039] 2. Displacement identification experiment:

[0040] (1) Experimental setup: Under open-loop control, the pressure of the hydraulic power source is set to P s =7MPa;

[0041] (2) Forward swing: Set the control input of the servo valve to u = 0.1 V and the duration to 5 s. At this time, the hydraulic motor starts to swing forward and the encoder records the angle change.

[0042] (3) Reverse swing: After 5 seconds, the control input of the servo valve is changed to u = -0.1V, and the duration is 5 seconds. The hydraulic motor swings in the reverse direction, and the encoder continues to record the angle change. Then, the control input is set to zero, and the pressure of the hydraulic power source is also set to zero, that is: u = 0V, P s =0MPa.

[0043] (4) Data processing: By processing the encoder sampling value, the angle and angular velocity curve output by the hydraulic motor can be obtained, such as Figure 2 As shown. Figure 2 , the angular velocity of the hydraulic motor is 11.5deg / s. Since it is a constant, according to flow = speed × displacement, we can get displacement = flow / speed. Now we need to get the flow without a flow meter. Considering the constant angular velocity, the angular acceleration is zero, that is, there is no inertial load; since there is no external load, the system is in a no-load state during the entire identification process, then the system flow can be obtained through the sample curve of the servo valve, that is, the rated flow. Therefore, the calculation result of the displacement is obtained, such as Figure 3As shown, taking the stable value after 5.2 seconds, the motor displacement value D is about 940cc / rad.

[0044] 3. Design of nonlinear control method:

[0045] (1) The precise motor displacement D obtained by identification is used as a known parameter and substituted into the model-based nonlinear control law to design a closed-loop control system.

[0046] according to Figure 6 The hydraulic principle diagram of the hydraulic motor is shown in Figure 1. When designing the model-based nonlinear control method, the motor displacement value D obtained in step 2 is introduced: First, consider the angle of the hydraulic motor to be γ and the load pressure P L =P1-P2, so the state variable is defined as Then the state equation of the system is given as

[0047]

[0048] In formula (1), V1 = V 10 +D γ is the control volume of the hydraulic motor V1 chamber, V 10 is the initial control volume of the V1 cavity;

[0049] V2=V 20 -D γ is the control volume of cavity V2, V 20 is the initial control volume of the V2 cavity;

[0050] D is the displacement of the motor, B is the viscous friction coefficient, β e is the effective bulk modulus of the hydraulic oil, K v is the flow coefficient of the servo valve, C t is the internal leakage coefficient of the hydraulic motor, u is the control input of the servo valve, and J is the inertia of the hydraulic motor shaft; here, s v (·) is a user-defined function:

[0051]

[0052] Definition: θ=[θ1, θ2, θ3, θ4, θ5] T =[D,B,β e K v ,β e D,β e C t ] T , then, formula (1) can be rewritten as:

[0053]

[0054] In formula (3): f1=(R1 / V1+R2 / V2), f2=(1 / V1+1 / V2)x2, f3=(1 / V1+1 / V2)x3.

[0055] Obviously, according to formula (3), in the design process of the model-based nonlinear control input u, parameters f1, f2, f3, and D are required. The prior art uses a parameter adaptive method to obtain D, however, this inevitably requires a parameter convergence time and requires the satisfaction of continuous excitation conditions. Importantly, considering the rigor of theoretical design, the D obtained by this method cannot be directly used to accurately calculate f1, f2, and f3, which will cause a large control error, especially when the hydraulic motor moves greatly.

[0056] This embodiment, by identifying the displacement D of the valve-controlled hydraulic motor control system in an open-loop state and using it in the design of a nonlinear control method in a closed-loop state, can accurately calculate the model parameters and multiple intermediate variables of the control input, while avoiding the parameter convergence time and continuous excitation conditions required by the parameter adaptive method, ensuring transient and steady-state control accuracy, and having a relatively obvious advantage.

[0057] The angle of the valve-controlled hydraulic motor is controlled by the nonlinear control method. As for the influence of the displacement parameter D, the traditional parameter adaptive method can only estimate θ1 and θ3, but cannot process the displacement D in f1, f2, and f3. However, these three variables are functions of D. Therefore, the traditional parameter adaptive method is not rigorous in estimating the displacement parameter D. The present invention is compared with the ordinary nonlinear control method, such as Figure 7 Obviously, after using displacement identification compensation, the comprehensive error of angle control is greatly reduced, the maximum error is reduced by 67.79%, the average error is reduced by 87.03%, and the error standard deviation is reduced by 72.95%.

[0058] Embodiment 2: Torque control system

[0059] 1. Experimental system construction

[0060] (1) Design an experimental platform including a hydraulic power source, a servo valve, a swing hydraulic motor, a stationary fixture, a controller, and a torque sensor, such as Figure 1 (b) shown; wherein the control input range of the servo valve used is -10V to +10V, the rated flow rate is 63L / min, the number is 2, the installation form is parallel, and the zero bias correction has been completed after leaving the factory;

[0061] (2) The flow rate from the hydraulic power source to the swing hydraulic motor is regulated by the control input of the servo valve, and the control range is set to -10V to +10V.

[0062] 2. Displacement identification experiment:

[0063] (1) Experimental setup: In the open loop state, the pressure of the hydraulic power source is set to P s =7MPa;

[0064] (2) Forward swing: Set the control input of the servo valve to u = 0.05V, and the duration is 5s. At this time, the hydraulic motor starts to swing forward, and observe and record the change in the torque value on the torque sensor. In this embodiment, the swing hydraulic motor is in the torque control mode. Since the motor shaft is fixed by the stationary fixture, the system has entered a steady state, and the angular velocity and angular acceleration of the hydraulic motor are both zero. Therefore, the relationship between torque and load pressure is directly used for displacement identification.

[0065] (3) Reverse swing: After 5 seconds, the control input of the servo valve is changed to u=-0.05V, and the duration is 5 seconds. The hydraulic motor swings in the reverse direction, and the torque sensor continues to record the change in torque value; then the control input is set to zero, and the power source pressure is also set to zero, that is: u=0V, P s =0MPa.

[0066] (4) Data processing: Based on the sampling value of the torque sensor, the torque curve output by the hydraulic motor can be obtained, such as Figure 4 As shown. Since torque = load pressure × displacement, and the load pressure will always be maintained at 7Mpa due to a long enough duration, then the motor displacement can be calculated without a pressure sensor through displacement = torque / load pressure, as shown in Figure 5 As shown, the displacement value D of the motor is obtained to be approximately 940cc / rad.

[0067] 3. Design of nonlinear control method:

[0068] Referring to Example 1, according to Figure 6 The hydraulic principle diagram in the embodiment 1 is used, and the motor displacement value obtained by step 2 is used as a known parameter to design and implement a nonlinear control strategy based on torque feedback, such as sliding mode control, adaptive control, etc., to improve control accuracy and stability. The specific design method of the nonlinear control method is the same as that of embodiment 1.

[0069] By using the above nonlinear control method, the torque of the valve-controlled hydraulic motor is controlled. The comparison method is as shown in Example 1. Figure 8 Obviously, after displacement identification compensation, the comprehensive error of torque control is greatly reduced, the maximum error is reduced by 6.48%, the average error is reduced by 14.83%, and the error standard deviation is reduced by 17.12%.

[0070] Through the above two specific embodiments, the embodiments of the present invention demonstrate how to accurately obtain the displacement value of the valve-controlled swing hydraulic motor in the angle control system and the torque control system through a simple experimental identification method, and apply it to the design of the nonlinear control system, thereby improving the control accuracy of the system and reducing the risk of instability.

[0071] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for accurately obtaining the displacement of a nonlinear control system of a valve-controlled swing hydraulic motor based on experimental identification, characterized in that The following steps are involved: S1 system construction: construct an experimental platform including hydraulic power source, servo valve, acquisition element, valve-controlled swing hydraulic motor and controller; S2 displacement identification: in the open-loop control state, the pressure of the hydraulic power source is set to a preset value; by controlling the input signal of the servo valve, the valve-controlled swing hydraulic motor generates a measurable movement or torque change; under the action of the servo valve input signal, the output data of the valve-controlled swing hydraulic motor is collected in real time through the collection element; According to the recorded data, combined with the rated flow or load pressure of the servo valve, the precise displacement of the hydraulic motor is obtained by calculation; S3 nonlinear control method design: The precise displacement obtained by S2 identification is used to design a model-based nonlinear control law to design a closed-loop control system.

2. The method according to claim 1, characterized in that The preset value of the hydraulic power source in step S2 is 7 MPa, but is not limited to this value and can be adjusted according to actual system requirements.

3. The method according to claim 1 or 2, characterized in that: In step S2, for the angle control system, the input signal of the servo valve includes a positive non-zero signal u and a negative non-zero signal -u, and each signal lasts for a predetermined time T.

4. The method according to claim 3, characterized in that In step S2, for the angle control system, the angle change data of the hydraulic motor is recorded by an encoder, and the angular velocity is calculated, and the angular velocity is used for subsequent displacement calculation.

5. The method according to claim 1 or 2, characterized in that: In step S2, for the torque control system, the input signal of the servo valve includes a positive non-zero signal u and a negative non-zero signal -u, and the duration and amplitude are adjusted according to the system characteristics.

6. The method according to claim 5, characterized in that In step S2, for the torque control system, the torque data output by the hydraulic motor is recorded by a torque sensor. At this time, the motor shaft of the hydraulic motor is fixed by a static fixture, and the angular velocity and angular acceleration are both zero. The torque data can be directly used for displacement calculation.

7. The method according to claim 4 or 6, characterized in that: In step S2, the calculation formula of the displacement is adjusted according to the specific system parameters and the measured values. For the angle control system, "displacement = (servo valve rated flow / angular velocity) × conversion factor" is used, where the conversion factor is used to convert the angular velocity unit from degrees / second to radians / second; for the torque control system, "displacement = torque / load pressure" is used.

8. A nonlinear control system for a valve-controlled swing hydraulic motor, characterized in that include: A hydraulic power source, a servo valve, a swing hydraulic motor, a collection element, and a controller implemented according to the method of any one of claims 1 to 7, wherein the controller uses the precise displacement obtained by experimental identification to design and execute a nonlinear control strategy.

9. The control system according to claim 7, characterized in that: Also included is a device for monitoring and regulating the pressure of the hydraulic power source to ensure that the power source pressure remains constant during the experimental identification process.

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