A fast fixed-time unmanned agricultural machinery path tracking control method, system and device considering input saturation

Abstract

The present invention discloses a fast fixed-time unmanned agricultural machinery path tracking control method, system and device considering input saturation, which are applied to the field of agricultural machinery such as tractors, rotary tillers, harvesters, etc. Under this control method, the path tracking accuracy of agricultural machinery is high, the robustness is strong, and the response speed is fast. The main steps are: (1) establishing a deviation motion model for the path tracking of unmanned agricultural machinery; (2) designing a fast fixed-time sliding mode so that the tracking deviation can converge quickly; (3) constructing an input saturation auxiliary function to offset the adverse effects of actuator saturation; (4) combining the input saturation auxiliary function with the sliding mode control to obtain an unmanned agricultural machinery path tracking composite controller considering input saturation. The present invention enables agricultural machinery to respond quickly under disturbance and improves the operation quality; it also solves the problem of actuator saturation caused by large gain, and maintains fast responsiveness and high-precision tracking performance.

Description

Technical Field

[0001] The present invention relates to the field of agricultural machinery control, and designs a fast fixed-time unmanned agricultural machinery path tracking control method, system and device that considers input saturation, so as to increase the path tracking accuracy of agricultural machinery, and at the same time ensure that agricultural machinery can respond quickly in actual complex operating environments, improve operating quality, and be closer to actual applications. Background Art

[0002] Many countries are studying unmanned agricultural machinery to solve the problem of food and labor shortages by adopting autonomous navigation technology to replace the heavy labor required for traditional agricultural production activities. Autonomous navigation technology of unmanned agricultural machinery is increasingly used in various agricultural production activities and has become a key technology for achieving precision agriculture. Tracking control is the key to improving the accuracy and stability of agricultural machinery autonomous navigation systems. Therefore, designing an efficient path tracking control method is of great significance to improving the tracking accuracy and robustness of agricultural machinery.

[0003] Sliding mode control is a commonly used robust control method for dealing with nonlinear uncertain systems. It has the advantages of simple implementation, fast dynamic response, and strong anti-interference ability. Therefore, many researchers choose sliding mode control to solve the path tracking problem of agricultural machinery.

[0004] However, most sliding mode control algorithms usually converge in a finite time, and the maximum convergence time depends on the initial conditions of the agricultural machinery, which will cause the tracking accuracy to increase with the increase of the initial error. Fast convergence time can support agricultural machinery to adapt to complex environments more quickly. Currently, the terminal sliding mode control algorithm with fixed time convergence has been used to improve the path tracking accuracy of agricultural machinery, but due to the existence of singularity problems and the failure to consider the transient response of the system, the convergence speed is limited. And due to the increase in convergence speed, the emergence of actuator saturation damages the tracking performance of agricultural machinery and system hardware. Summary of the invention

[0005] In order to solve the above-mentioned deficiencies in the prior art, that is, the inability to improve the tracking accuracy and rapid responsiveness of agricultural machinery under the premise of considering the input saturation problem, it is urgent to design a path tracking control algorithm suitable for agricultural machinery and its corresponding system and device, so as to ensure the dynamic performance and tracking accuracy of the path tracking of unmanned agricultural machinery, improve the rapid response of agricultural machinery and reduce the impact of the actuator saturation problem. Therefore, the present invention proposes a fast fixed-time unmanned agricultural machinery path tracking control method, system and device considering input saturation.

[0006] The present invention achieves the above technical objectives through the following technical means.

[0007] A fast fixed-time unmanned agricultural machinery path tracking control method considering input saturation comprises the following steps:

[0008] Step (1), according to the movement characteristics of the unmanned agricultural machinery, a deviation movement model of lateral deviation and heading deviation with input saturation characteristics is established, and the required state variables are defined;

[0009] Step (2), designing a fast fixed time controller to ensure that the lateral deviation and heading deviation of the unmanned agricultural machinery can be adaptively and quickly converged within a fixed time, and ensuring the non-singularity of the system by designing a sliding mode switching regulator;

[0010] Step (3), constructing an input saturation auxiliary function according to the actuator saturation problem existing in the deviation motion model to offset the adverse effects caused by the saturation characteristics;

[0011] Step (4), combining the fast fixed time controller with the input saturation auxiliary function, and designing a fast fixed time composite controller for unmanned agricultural machinery path tracking taking into account input saturation, so that the agricultural machinery can track the desired path efficiently and quickly.

[0012] Furthermore, the deviation motion model is:

[0013]

[0014] Among them, e l 、e θ It represents the lateral deviation and heading deviation generated when the agricultural machinery tracks the expected path, V is the longitudinal speed of the agricultural machinery, and L t is the wheelbase between the front and rear wheels of agricultural machinery, r t is the curvature radius of the point on the desired path closest to the midpoint of the rear wheel axle of the agricultural machinery, δ sat is an asymmetric saturation function;

[0015] and:

[0016] e l =-(x t -x d )sinθ d +(y t -y d )cosθ d

[0017] e θ =θ t -θ d

[0018] Among them, [x t ,y t ] Tis the position vector of the unmanned autonomous driving agricultural machinery, θ t is the heading angle of the agricultural machinery, [x d ,y d ] T Represents the position vector of the point on the desired path closest to the midpoint of the rear wheel axle of the agricultural machinery, θ d is the desired heading angle.

[0019] Furthermore, the asymmetric saturation function is:

[0020]

[0021] in, δ、

[0022] δ are the upper and lower limits of the actuator amplitude, tanh represents the hyperbolic tangent function, atanh represents the inverse hyperbolic tangent function, is a bounded approximation error, that is ρ0 is a known positive number, and δ is the front wheel steering angle command.

[0023] Furthermore, the fast fixed time controller is constructed by the following fast fixed time sliding mode:

[0024]

[0025] Among them, x1 and x2 represent the state vector of the system, and x1=e l , x2=Vsine θ ; φ 1s ,φ 2s is the system gain, and φ 1s >0,φ 2s >0; Δ(x1) is the adaptive gain, η1(x1) and η2(x1) are fixed-time sliding mode switching adjustment items.

[0026] Furthermore, the adaptive gain is:

[0027]

[0028] Among them, 0<(<1, λ1>0, λ2 is an even number.

[0029] Furthermore, the sliding mode switching regulator is:

[0030]

[0031] in, is represented as a fixed-time sliding surface, and

[0032] 0.05, intermediate Intermediate

[0033] Furthermore, the input saturation auxiliary function Has the following form:

[0034]

[0035] Among them, u sat =tanδ sat represents a virtual control input with saturation characteristics, u = tanδ is the control law to be designed,

[0036] β1>1, 1 / 2<β2<1, α1, α2, α3 are positive coefficients.

[0037] Furthermore, the fast fixed-time compound controller has the following form:

[0038]

[0039] in, It is an adaptive gain that can be automatically adjusted according to system variables. ι1>1, 1 / 2<ι2<1, φ1>0, φ2>0;

[0040] Has the following form:

[0041]

[0042] A fast fixed-time unmanned agricultural machinery path tracking control system considering input saturation, comprising:

[0043] Fast fixed time control module, used to enable agricultural machinery to quickly track the desired path, ensuring the efficiency and speed of agricultural machinery;

[0044] Input saturation auxiliary function module, used to offset the adverse effects of input saturation and ensure the hardware safety and control accuracy of agricultural machinery under input saturation conditions;

[0045] An adaptive gain adjustment module is used to improve the lateral deviation of agricultural machinery and the transient convergence speed of the lateral deviation when it is about to converge to the sliding surface;

[0046] The sliding mode switching regulator module is used to solve the singularity problem of terminal sliding mode;

[0047] Disturbance compensation module to counteract lumped disturbances caused by external disturbances and unmodeled dynamics;

[0048] The deviation conversion module is used to convert the current position coordinates of the agricultural machinery and the current nearest expected path coordinates into lateral deviation and heading deviation.

[0049] A fast fixed-time unmanned agricultural machinery path tracking control device considering input saturation, characterized in that it comprises:

[0050] Host computer, used to design control programs and record experimental data;

[0051] RTK signal base station, used to obtain the global position information of the current working scene of agricultural machinery;

[0052] The path planning unit is used to design the desired path that the agricultural machinery needs to follow and calculate the lateral deviation and heading deviation information based on the real-time position information of the vehicle;

[0053] Satellite navigation and positioning system, used to obtain real-time location information of agricultural machinery;

[0054] Serial communication unit, used to realize communication between various parts of agricultural machinery, receiving and sending various information;

[0055] The hardware control unit receives the lateral deviation and heading deviation information, calculates the control program and outputs the turning angle control command; the vehicle control unit is used to execute the turning angle command of the agricultural machinery to realize the vehicle's forward movement and turning.

[0056] The beneficial effects achieved by the present invention are:

[0057] 1. The sliding mode switching regulator is used to solve the singularity problem of the general terminal sliding mode and ensure the continuity of the sliding mode surface in the neighborhood near 0. It not only improves the robustness of agricultural machinery, but also improves the convergence speed of the system through adaptive adjustment of the gain.

[0058] 2. The use of fast fixed-time sliding mode control allows the lateral deviation and heading deviation of agricultural machinery to converge quickly within a fixed time, which improves the online time of agricultural machinery path tracking control, thereby significantly improving the rapidity of agricultural machinery path tracking and ensuring its excellent dynamic performance and control accuracy.

[0059] 3. The use of input saturation auxiliary function combined with fast fixed-time sliding mode composite control not only offsets the adverse effects caused by actuator saturation, but also ensures the hardware safety of agricultural machinery and improves the tracking accuracy of unmanned agricultural machinery under the influence of input saturation. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1It is a schematic diagram of the control scheme of the present invention;

[0061] Figure 2 It is a schematic diagram of the device composition of the present invention;

[0062] Figure 3 It is a schematic diagram of the system structure of the present invention;

[0063] Figure 4 The agricultural machinery path tracking curve diagram of the present invention;

[0064] Figure 5 A lateral deviation map for path tracking of agricultural machinery of the present invention;

[0065] Figure 6 This is the agricultural machinery path tracking heading deviation map of the present invention. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the technical solution in the examples of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. It should be noted that the described embodiments are only some embodiments of the present invention, not all embodiments. They are only used to explain the present invention, but not to limit the present invention.

[0067] The present invention provides a fast fixed-time unmanned agricultural machinery tracking control method, system and device considering input saturation. The overall control scheme schematic diagram is shown in Figure 1 shown.

[0068] The device consists of Figure 2 As shown, it will be used to specifically illustrate the present invention, including the following parts:

[0069] The host computer realizes the writing and debugging of the control program of the present invention, writes the control algorithm into the hardware control unit through the CAN bus, and records the working information of the agricultural machinery through real-time communication;

[0070] The RTK signal base station uses a real-time differential positioning system to collect the global position data of the current working scene of the agricultural machinery, and transmits the acquired data to the path planning unit of the agricultural machinery through wireless communication;

[0071] Satellite navigation positioning system, using the vehicle-mounted Beidou navigation system to obtain the real-time location information of agricultural machinery, and communicate with the path planning unit in real time through RS232;

[0072] The path planning unit plans the expected path of the agricultural machinery through data analysis and fusion processing of various data information and calculates the lateral deviation and heading deviation information based on the real-time position information of the vehicle;

[0073] Serial communication unit, which realizes data communication and command transmission between various levels of agricultural machinery through CAN bus, RS232 and wireless communication;

[0074] The hardware control unit uses the STM32 single-chip microcomputer to calculate the control program of the present invention and output the turning angle control command based on the lateral deviation and heading deviation information received through the CAN bus, and communicates the current position, heading and other information with the host computer in real time;

[0075] The vehicle control unit, as the controlled object at the bottom layer of the entire device, outputs the corner control command through the electronically controlled chassis to complete the turning action of the agricultural machinery.

[0076] For the embodiment of the above device, an embodiment of a fast fixed-time unmanned agricultural machinery path tracking control system considering input saturation is as follows: Figure 3 As shown, it includes the following modules:

[0077] Fast fixed time control module, used to enable agricultural machinery to quickly track the desired path, ensuring the efficiency and speed of agricultural machinery;

[0078] Input saturation auxiliary function module, used to offset the adverse effects of input saturation and ensure the hardware safety and control accuracy of agricultural machinery under input saturation conditions;

[0079] An adaptive gain adjustment module is used to improve the lateral deviation of agricultural machinery and the transient convergence speed of the lateral deviation when it is about to converge to the sliding surface;

[0080] The sliding mode switching regulator module is used to solve the singularity problem of terminal sliding mode;

[0081] The disturbance compensation module is used to achieve appropriate compensation for the lumped disturbance caused by external disturbances and unmodeled dynamics;

[0082] The deviation conversion module is used to convert the current position coordinates of the agricultural machinery and the current nearest expected path coordinates into lateral deviation and heading deviation.

[0083] For the embodiment of the above system, an embodiment of a fast fixed-time unmanned agricultural machinery path tracking control method considering input saturation includes the following specific contents:

[0084] (1) According to the motion characteristics of unmanned agricultural machinery, a deviation motion model of lateral deviation and heading deviation with input saturation characteristics is established, and the required state variables are defined;

[0085] Specifically, in this example, the deviation motion model of agricultural machinery with input saturation problem is:

[0086]

[0087] Among them, e l , eθ represents the lateral deviation and heading deviation generated when the agricultural machinery tracks the expected path, V is the longitudinal speed of the agricultural machinery, L t is the wheelbase between the front and rear wheels of the agricultural machinery, and rt is the radius of curvature of the point on the desired path closest to the midpoint of the rear wheel axle of the agricultural machinery.

[0088] In addition, l 、e θ The mathematical model can be expressed as:

[0089] e l =-(x t -x d )sinθ d +(y t -y d )cosθ d

[0090] e θ =θ t -θ d

[0091] Among them, [x t ,y t ] T is the position vector of the unmanned autonomous driving agricultural machinery, θ t is the heading angle of the agricultural machinery, [x d ,y d ] T Represents the position vector of the point on the desired path closest to the midpoint of the rear wheel axle of the agricultural machinery, θ d is the desired heading angle.

[0092] At the same time, the actual control input δ sat Affected by the saturation nonlinearity, a new saturation function is designed as follows:

[0093]

[0094] in, δ , are the upper and lower limits of the actuator amplitude, tanh represents the hyperbolic tangent function, atanh represents the inverse hyperbolic tangent function, is a bounded approximation error, that is ρ0 is a known positive number, and δ is the front wheel steering angle command, which can be regarded as the only control input.

[0095] The innovation of the saturation function design lies in that the designed saturation function can be expressed as the modeling of the actuator saturation problem with asymmetric upper and lower amplitudes, which is closer to actual engineering.

[0096] (2) Design a fast fixed time sliding mode, which is:

[0097]

[0098] Among them, x1 and x2 represent the state vector of the system, and x1=e l , x2=Vsine θ , Δ(x1) is the adaptive gain, η1(x1) and η2(x1) are fixed-time sliding mode switching adjustment items, φ 1s ,φ 2s is the system gain, and φ 1s >0,φ 2s >0.

[0099] The innovation of this fast fixed-time sliding mode design is that it can ensure that the tracking deviation converges quickly within a fixed time, and when the sliding surface converges to the neighborhood around the origin, the proposed control scheme can obtain a shorter convergence time by considering the transient response of the tracking deviations x1 and x2.

[0100] At the same time, an adaptive gain is designed, which is:

[0101]

[0102] Among them, 0<(<1, λ1>0, λ2 is an even number.

[0103] The innovation of this adaptive gain design is that the gain can be dynamically adjusted according to the size of the tracking deviation, which improves the dynamic performance of the system and shortens the convergence time.

[0104] Then the sliding mode switching regulator is designed to ensure the non-singularity of the system, namely:

[0105]

[0106] in, is represented as a fixed-time sliding surface, and

[0107] also, is a very small positive number, in this embodiment, it is 0.05, and the intermediate value Intermediate

[0108] The innovation of the sliding mode switching regulator design is that it can ensure the continuity of the system in the neighborhood near 0, which not only effectively improves the rapid responsiveness of agricultural machinery path tracking, but also improves the robustness of the system while ensuring tracking performance.

[0109] (3) According to the actuator saturation problem existing in the deviation motion model, an input saturation auxiliary function is constructed to effectively offset the adverse effects caused by the saturation characteristics; the input saturation auxiliary function Specifically designed as:

[0110]

[0111] Among them, u sat =tanδ sat represents a virtual control input with saturation characteristics, u = tan is the control law to be designed, β1>1, 1 / 2<β2<1, α1, α2, α3 are positive coefficients.

[0112] Input saturation helper function The innovation lies in: by introducing the saturation term u sat -u, which can convert the virtual control law with input saturation characteristics into the actual control law. On the one hand, it can effectively alleviate the input saturation problem in the fast fixed time tracking control of agricultural machinery without reducing the system performance. On the other hand, for agricultural machinery, the designed input saturation auxiliary function The hardware safety of agricultural machinery is ensured and the path tracking accuracy of agricultural machinery under saturation characteristics is improved.

[0113] (4) Combine the fast fixed-time controller with the input saturation auxiliary function to design a fast fixed-time unmanned agricultural machinery path tracking composite controller considering input saturation;

[0114] Design a fast fixed-time unmanned agricultural machinery path tracking composite controller considering input saturation as:

[0115]

[0116] in, It is an adaptive gain that can be automatically adjusted according to system variables. ι1>1, 1 / 2<ι2<1, φ1>0, φ2>0. also, Has the following form:

[0117]

[0118] An embodiment of a fast fixed-time unmanned agricultural machinery path tracking control method, system and device considering input saturation has been specifically explained and illustrated, so that the technical solution is clearer and easier for engineers to implement. Based on this example, the effect of the present invention is further demonstrated through experiments.

[0119] In order to verify that the present invention has excellent tracking accuracy, the tracking accuracy of the embodiment is tested based on the path tracking performance when the initial lateral deviation of the unmanned agricultural machinery is set to 30 cm. Figure 4-Figure 6 As shown, it is not difficult to see that the control accuracy of this embodiment in the experiment is higher and it can track the reference path in a shorter time, so it can be demonstrated that the present invention has excellent tracking accuracy. In summary, the present invention achieves a significant improvement in dynamic performance and tracking accuracy while ensuring the hardware safety of agricultural machinery.

[0120] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0121] Although the present invention has been described according to various specific embodiments, those skilled in the art will appreciate that the present invention can be implemented with modifications within the spirit of the claims. Therefore, any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention belong to the protection scope of the present invention.

Claims

1. A fast fixed-time unmanned agricultural machinery path tracking control method considering input saturation, characterized in that: The following steps are involved: Step (1), according to the movement characteristics of the unmanned agricultural machinery, a deviation movement model of lateral deviation and heading deviation with input saturation characteristics is established, and the required state variables are defined; The deviation motion model is: Among them, e l 、e θ It represents the lateral deviation and heading deviation generated when the agricultural machinery tracks the expected path, V is the longitudinal speed of the agricultural machinery, and L t is the wheelbase between the front and rear wheels of agricultural machinery, r t is the curvature radius of the point on the desired path closest to the midpoint of the rear wheel axle of the agricultural machinery, δ sat is an asymmetric saturation function; and: e ι =-(x t -x d )sinθ d +(y t -y d )cosθ d e θ =θ t -θ d Among them, [x t ,y t ] T is the position vector of the unmanned autonomous driving agricultural machinery, θ t is the heading angle of the agricultural machinery, [x d ,y d ] T Represents the position vector of the point on the desired path closest to the midpoint of the rear wheel axle of the agricultural machinery, θ d is the desired heading angle; The asymmetric saturation function is: in, δ、 are the upper and lower limits of the actuator amplitude, tanh represents the hyperbolic tangent function, atanh represents the inverse hyperbolic tangent function, is a bounded approximation error, that is ρ0 is a known positive number, δ is the front wheel steering angle command; Step (2), designing a fast fixed time controller to ensure that the lateral deviation and heading deviation of the unmanned agricultural machinery can be adaptively and quickly converged within a fixed time, and ensuring the non-singularity of the system by designing a sliding mode switching regulator; The fast fixed time controller is constructed by the following fast fixed time sliding mode: Among them, x1 and x2 represent the state vector of the system, and x1=e l , x2=Vsine θ ; φ 1s ,φ 2s is the system gain, and φ 1s >0,φ 2s >0; Δ(x1) is the adaptive gain, η1(x1) and η2(x1) are fixed-time sliding mode switching adjustment items; The adaptive gain is: Among them, 0<ζ<1, λ1>0, λ2 is an even number; The sliding mode switching regulator is: in, is represented as a fixed-time sliding surface, and 0.05, intermediate amount Intermediate i=1,2, Step (3), constructing an input saturation auxiliary function according to the actuator saturation problem existing in the deviation motion model to offset the adverse effects caused by the saturation characteristics; The input saturation auxiliary function θ has the following form: Among them, u sat =tanδ sat represents a virtual control input with saturation characteristics, u = tanδ is the control law to be designed, β1>1, 1 / 2<β2<1, α1, α2, α3 are positive coefficients; Step (4), combining the fast fixed time controller with the input saturation auxiliary function to design a fast fixed time composite controller for unmanned agricultural machinery path tracking considering input saturation, so that the agricultural machinery can track the desired path efficiently and quickly; The fast fixed-time compound controller has the following form: in, It is an adaptive gain that can be automatically adjusted according to system variables. ι1>1, 1 / 2<ι2<1, φ1>0, φ2>0; Has the following form:

2. A system for implementing the fast fixed-time unmanned agricultural machinery path tracking control method considering input saturation as described in claim 1, characterized in that: include: Fast fixed time control module, used to enable agricultural machinery to quickly track the desired path, ensuring the efficiency and speed of agricultural machinery; Input saturation auxiliary function module, used to offset the adverse effects of input saturation and ensure the hardware safety and control accuracy of agricultural machinery under input saturation conditions; An adaptive gain adjustment module is used to improve the lateral deviation of agricultural machinery and the transient convergence speed of the lateral deviation when it is about to converge to the sliding surface; The sliding mode switching regulator module is used to solve the singularity problem of terminal sliding mode; Disturbance compensation module to counteract lumped disturbances caused by external disturbances and unmodeled dynamics; The deviation conversion module is used to convert the current position coordinates of the agricultural machinery and the current nearest expected path coordinates into lateral deviation and heading deviation.

3. A device for implementing the fast fixed-time unmanned agricultural machinery path tracking control method considering input saturation as described in claim 1, characterized in that: include: Host computer, used to design control programs and record experimental data; RTK signal base station, used to obtain the global position information of the current working scene of agricultural machinery; The path planning unit is used to design the desired path that the agricultural machinery needs to follow and calculate the lateral deviation and heading deviation information based on the real-time position information of the vehicle; Satellite navigation and positioning system, used to obtain real-time location information of agricultural machinery; Serial communication unit, used to realize communication between various parts of agricultural machinery, receiving and sending various information; A hardware control unit receives lateral deviation and heading deviation information, calculates control programs and outputs turning angle control commands; The vehicle control unit is used to execute the turning commands of agricultural machinery to enable the vehicle to move forward and turn.

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