Method for obtaining accurate displacement of nonlinear control system of valve-controlled swing hydraulic motor based on experimental identification and implementation system thereof

Abstract

The present application relates to the technical field of hydraulic transmission and control, in particular to a valve-controlled swing hydraulic motor nonlinear control system displacement accurate acquisition method and its implementation system based on experimental identification. The present application accurately acquires the displacement parameters of the valve-controlled swing hydraulic motor in an open loop state through experimental identification means before the valve-controlled swing hydraulic motor nonlinear control system formally enters a closed loop control, without increasing additional sensors, and uses the acquired accurate displacement to design a model-based nonlinear control law for the design of the closed loop control system. The method of the present application can effectively overcome the problem of control precision decline caused by uncertain displacement, while avoiding the parameter convergence time and continuous excitation conditions required by the parameter adaptive method, ensuring the transient and steady state control precision, and significantly improving the control precision and stability of the system.

Description

Technical Field

[0001] This invention relates to the field of hydraulic transmission and control technology, specifically to a method and implementation system for accurately acquiring the displacement of a valve-controlled oscillating hydraulic motor nonlinear control system based on experimental identification. This invention, through experimental identification, accurately acquires the displacement parameters of a valve-controlled oscillating hydraulic motor without adding additional sensors, thereby significantly improving the accuracy and stability of the control system. Background Technology

[0002] A valve-controlled oscillating hydraulic motor, also known as an oscillating hydraulic cylinder, is a special hydraulic actuator whose output shaft can perform reciprocating oscillating (rather than continuous rotational) motion. This type of motor plays a crucial role in hydraulic systems, especially in applications requiring finite rotational motion and high torque. Valve-controlled oscillating hydraulic motor control systems are widely used in special robots, port machinery, and aerospace due to their advantages such as high power density, fast dynamic response, and small installation space requirements. However, achieving high-precision control of valve-controlled hydraulic motors requires overcoming not only the inherent pressure-flow nonlinearity of servo valves but also addressing the parameter uncertainties and uncertain nonlinearities present in the entire system. Clearly, linear control methods such as PID control are insufficient to handle these challenges, while model-based nonlinear control methods offer inherent advantages.

[0003] Displacement is a key parameter in the nonlinear control system of valve-controlled hydraulic motors, playing a crucial role in the design of nonlinear control methods. 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, obtaining the accurate displacement of the motor is essential. However, in situations where the theoretical design displacement cannot be obtained, such as in some modification projects, the displacement parameter becomes unknown. Currently, treating motor displacement as a parameter uncertainty and performing adaptive estimation is a common approach. The motor displacement is estimated using parameter adaptive methods and then used in the design of nonlinear control methods for valve-controlled oscillating hydraulic motor control systems. This method mainly has the following drawbacks:

[0004] 1. When the motor displacement is completely unknown, and there is no set criterion for parameter adaptive rate, an unreasonable displacement convergence speed will limit the transient control accuracy of the valve-controlled oscillating hydraulic motor control system. Furthermore, the parameter adaptive method also needs to satisfy continuous excitation conditions, which further limits its widespread application.

[0005] 2. Existing research methods cannot handle changes in the control volume of oscillating hydraulic motors. While steady-state motor displacement can usually be obtained through parameter adaptation and when continuous excitation conditions are met, the control volume changes with the motor's position. If this method is applied, the motor displacement used to calculate the real-time control volume in the nonlinear control design process is not obtained through parameter adaptation, but rather a nominal value is substituted or it is simply ignored, leading to sloppiness in the nonlinear control design process. This is especially true when the hydraulic motor moves significantly, causing even more drastic changes in the control volume and resulting in substantial variations in model parameters. The inability to obtain accurate motor displacement values ​​will significantly reduce control accuracy. Furthermore, the requirement for satisfying excitation conditions in existing parameter adaptation methods is also a limiting factor in practical applications.

[0006] Therefore, it is essential to explore a new method to obtain a more accurate motor displacement in order to improve control precision.

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

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

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

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

[0011] S1 System Setup: Construct an experimental platform that includes a hydraulic power source, servo valve, data acquisition components, valve-controlled swing hydraulic motor, and controller;

[0012] S2 displacement identification:

[0013] S21 Experimental Setup: In open-loop control mode, 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 is made to generate measurable motion or torque changes; under the action of the input signal of the servo valve, the output data of the valve-controlled swing hydraulic motor is acquired in real time through the acquisition element;

[0015] S23 Data Processing: Based on the collected data and combined with the rated flow or load pressure of the servo valve, the precise displacement of the hydraulic motor is calculated.

[0016] S3 Nonlinear Control Method Design: The precise displacement identified by S2 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 oscillating hydraulic motor nonlinear control system, comprising: a hydraulic power source, a servo valve, an oscillating hydraulic motor, a data acquisition element, and a controller implemented according to the method of the first aspect above, wherein the controller designs and executes a nonlinear control strategy using the precise displacement obtained by experimental identification.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. High-precision control: The precise value of motor displacement obtained through experimental identification enables more accurate calculation of 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 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. No additional measuring components are required, which reduces the system complexity and cost.

[0021] 3. Avoiding the limitations of parameter adaptation: Traditional parameter adaptation methods require continuous excitation conditions, and the displacement convergence speed may be unreasonable, affecting transient control accuracy. This method performs displacement identification in open-loop mode, avoiding these problems.

[0022] 4. Improved system stability: Precise motor displacement values ​​allow for more rigorous design of nonlinear control methods, enabling better handling of system parameter variations and uncertain nonlinear issues, thereby improving the overall stability of the system. Attached Figure Description

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

[0024] Figure 2 According to Embodiment 1 of this application, the angle and angular velocity output by the valve-controlled hydraulic swing motor angle control system are shown;

[0025] Figure 3 According to Embodiment 1 of this application, the displacement identification result of the valve-controlled hydraulic swing motor angle control system is shown;

[0026] Figure 4 According to Embodiment 2 of this application, the torque output by the valve-controlled hydraulic swing motor torque control system is shown;

[0027] Figure 5 According to Embodiment 2 of this 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 this application, a schematic diagram of a nonlinear control system for a valve-controlled hydraulic swing motor is shown;

[0029] Figure 7 According to Embodiment 1 of this application, a result diagram of a valve-controlled hydraulic swing motor angle control system is shown;

[0030] Figure 8 According to Embodiment 2 of this application, a result diagram of a valve-controlled hydraulic swing motor torque control system is shown. Detailed Implementation

[0031] The technical features and advantages of this application will be described in more detail below with reference to the accompanying drawings, so that the advantages and features of this application can be more easily understood by those skilled in the art, thereby making a clearer and more explicit definition of the scope of protection of this invention.

[0032] This invention addresses the issue of uncertain motor displacement parameters in the design of nonlinear control systems for valve-controlled oscillating hydraulic motors, including angle control and torque control. It proposes a method for accurately identifying motor displacement through experiments. For the angle control system, only a single sensor—an encoder—is required for identification; for the torque control system, only a single sensor—a torque sensor—is needed. Regardless of whether it's an angle or torque control system, no additional components are required to obtain accurate motor displacement before entering closed-loop control. This accurate displacement can then be used in the design of nonlinear control methods, achieving high-performance closed-loop control while ensuring the rigor of theoretical derivations.

[0033] To achieve the above objectives, the basic idea of ​​this invention is as follows: By identifying the displacement of the valve-controlled swing hydraulic motor control system in the open-loop control state, and then introducing the identified precise displacement of the motor into the design of the nonlinear control method in the closed-loop state, the model parameters of the control input and multiple intermediate variables can be accurately calculated. At the same time, the parameter convergence time and continuous excitation conditions required by the parameter adaptive method are avoided, ensuring the transient and steady-state control accuracy, which has obvious advantages.

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

[0035] Example 1: Angle Control System

[0036] 1. Experimental system setup:

[0037] (1) Design an experimental platform that includes a hydraulic power source, servo valve, swing hydraulic motor, encoder, and controller, such as Figure 1 As shown in (a); the control input range of the servo valves used is -10V to +10V, the rated flow rate is 63L / min, the quantity is 2, the installation form is parallel, and the zero offset calibration 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 oscillation: Set the control input of the servo valve to u = 0.1V for 5s. At this time, the hydraulic motor starts to oscillate in the forward direction, and the encoder records the angle change.

[0042] (3) Reverse oscillation: After 5 seconds, change the control input of the servo valve to u = -0.1V for 5 seconds. The hydraulic motor oscillates in the reverse direction, and the encoder continues to record the angle change. Then, reset the control input to zero, and also reset the pressure of the hydraulic power source to zero, i.e., u = 0V, P s =0MPa.

[0043] (4) Data Processing: By processing the encoder's sampled values, the angle and angular velocity curves output by the hydraulic motor can be obtained, such as... Figure 2 As shown. According to Figure 2 The angular velocity of the hydraulic motor was found to be 11.5 deg / s. Since this is a constant value, according to the formula Flow rate = Velocity × Displacement, we can obtain Displacement = Flow rate / Velocity. The next step is to obtain the flow rate without a flow meter. Considering the constant angular velocity, the angular acceleration is zero, meaning there is no inertial load. Since there is no external load, the system is in an unloaded state throughout the identification process. Therefore, the system flow rate can be obtained from the sample curve of the servo valve, i.e., the rated flow rate. Thus, the displacement calculation result is obtained, as follows... Figure 3As shown, the stable value after 5.2 seconds is taken, and the motor displacement value D is approximately 940cc / rad.

[0044] 3. Design of nonlinear control methods:

[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 schematic diagram is used. When designing a model-based nonlinear control method, the motor displacement value D obtained in step 2 is introduced: First, consider the angle of the hydraulic motor as γ and the load pressure P. L =P1-P2, therefore the state variable is defined as Then the system's state equation is given as follows:

[0047]

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

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

[0050] D is the motor displacement, B is the coefficient of viscous friction, and β is the coefficient of friction. e It is the effective bulk modulus of hydraulic oil, k v C is the flow coefficient of the servo valve. t is the internal leakage coefficient of the hydraulic motor, u is the control input of the servo valve, and J is the moment of 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 Kv , β e D,β e Ct ] T Therefore, equation (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] Clearly, according to equation (3), parameters f1, f2, f3, and D are required in the design process of the model-based nonlinear control input u. Existing technologies use an adaptive parameter method to obtain D; however, this inevitably requires a parameter convergence time and must satisfy the continuous excitation condition. 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 significant control errors, especially when the hydraulic motor moves at large amplitudes.

[0056] This embodiment identifies the displacement D of the valve-controlled hydraulic motor control system in the open-loop state and uses it to design a nonlinear control method in the closed-loop state. This allows for the accurate calculation of the model parameters of the control input and multiple intermediate variables. At the same time, it avoids the parameter convergence time and continuous excitation conditions required by the parameter adaptive method, ensuring transient and steady-state control accuracy, which has significant advantages.

[0057] The aforementioned nonlinear control method is used to control the angle of a valve-controlled hydraulic motor. Regarding the influence of the displacement parameter D, traditional parameter adaptive methods can only estimate θ1 and θ3, but cannot handle the displacement D in f1, f2, and f3. However, these three variables are all functions of D; therefore, the estimation of the displacement parameter D by traditional parameter adaptive methods is not rigorous. This invention compares with ordinary nonlinear control methods, such as... Figure 7 As shown in the figure, it is clear that after adopting displacement identification compensation, the overall angle control error is significantly reduced, with the maximum error reduced by 67.79%, the average error reduced by 87.03%, and the standard deviation of the error reduced by 72.95%.

[0058] Example 2: Torque Control System

[0059] 1. Experimental System Setup

[0060] (1) Design an experimental platform that includes a hydraulic power source, servo valve, swing hydraulic motor, static fixture, controller, and torque sensor, such as Figure 1 (b) shows that the control input range of the servo valves used is -10V to +10V, the rated flow rate is 63L / min, the quantity is 2, the installation form is parallel, and the zero offset calibration 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 open-loop mode, the pressure of the hydraulic power source is set to P. s =7MPa;

[0064] (2) Forward oscillation: Set the control input of the servo valve to u = 0.05V for 5 seconds. At this time, the hydraulic motor begins to oscillate forward, and observe and record the change in torque value on the torque sensor. In this embodiment, in 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 displacement is directly identified using the relationship between torque and load pressure.

[0065] (3) Reverse oscillation: After 5 seconds, change the control input of the servo valve to u = -0.05V for 5 seconds. The hydraulic motor oscillates in the reverse direction, and the torque sensor continues to record the torque value change; then, reset the control input to zero and the power source pressure to zero, i.e., u = 0V, P s =0MPa.

[0066] (4) Data Processing: Based on the sampled values ​​from 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 remain at 7 MPa due to the sufficiently long duration, the motor displacement can be calculated without a pressure sensor using displacement = torque / load pressure. Figure 5 As shown, the motor displacement value D is approximately 940cc / rad.

[0067] 3. Design of nonlinear control methods:

[0068] Referring to Example 1, according to Figure 6 The hydraulic schematic diagram in the example uses the motor displacement value identified in step 2 as a known parameter to design and implement a nonlinear control strategy based on torque feedback, such as sliding mode control or adaptive control, to improve control accuracy and stability. The specific design method for the nonlinear control method is the same as in Example 1.

[0069] The torque control of the valve-controlled hydraulic motor is achieved using the aforementioned nonlinear control method. The comparison method is referenced in Example 1. Figure 8 As shown in the figure, it is clear that after adopting displacement identification compensation, the overall torque control error is significantly reduced, with the maximum error decreasing by 6.48%, the average error decreasing by 14.83%, and the standard deviation of the error decreasing by 17.12%.

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

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

Claims

1. A method for accurately obtaining the displacement of a valve-controlled swing hydraulic motor nonlinear control system based on experimental identification, characterized in that... Includes the following steps: S1 System Setup: Construct an experimental platform that includes a hydraulic power source, servo valve, data acquisition components, valve-controlled swing hydraulic motor, and controller; S2 Displacement Identification: In open-loop control mode, 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 is made to generate 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 by the acquisition element. Based on the recorded data and the rated flow rate or load pressure of the servo valve, the precise displacement of the hydraulic motor is calculated. S3 Nonlinear Control Method Design: The precise displacement identified by S2 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 7MPa, but it is not limited to this value and can be adjusted according to the 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, each signal lasting 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 the encoder, and the angular velocity is calculated. This 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, the duration and amplitude of which 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 the torque sensor. At this time, the motor shaft of the hydraulic motor is fixed by the 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 formula for calculating displacement is adjusted according to specific system parameters and measured values. For angle control systems, the formula is "Displacement = (Servo valve rated flow / angular velocity) × conversion factor", where the conversion factor is used to convert the angular velocity unit from degrees / second to radians / second. For torque control systems, the formula is "Displacement = Torque / Load pressure".

8. A nonlinear control system for a valve-controlled swing hydraulic motor, characterized in that... include: The method comprises a hydraulic power source, a servo valve, a swing hydraulic motor, a data acquisition element, and a controller implemented according to any one of claims 1 to 7, wherein the controller designs and executes a nonlinear control strategy using an experimentally identified precise displacement.

9. The control system according to claim 7, characterized in that, It also includes 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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