Unmanned agricultural machine second-order sliding mode path tracking control method and system considering input time delay

Abstract

The invention discloses an unmanned agricultural machine second-order sliding mode path tracking control method and system considering input time delay, and the method comprises the steps: constructing a deviation dynamic model containing transverse deviation and course deviation of an input time delay feature, and defining a state variable of an unmanned agricultural machine path tracking process; designing an input time delay estimator, and carrying out online estimation on unknown input time delay; constructing a compensation system suitable for unknown input time delay based on an input time delay estimator; a novel second-order sliding mode system without input time delay is constructed by a compensation system, a novel composite second-order sliding mode controller for path tracking of the unmanned agricultural machinery is designed by combining the compensation amount of the second-order sliding mode controller, and the unmanned agricultural machinery in actual operation is controlled to track an expected path. According to the method, the problem of control deviation caused by unknown input signal delay is solved, rapid responsiveness and high-precision tracking performance are kept, the agricultural machine can track the operation path with high precision under the condition of complex disturbance, and the operation quality is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of agricultural machinery control, and relates to a second-order sliding mode path tracking control method and system for unmanned agricultural machinery taking input delay into consideration. Background Art

[0002] Globally, many countries are working on developing unmanned agricultural machinery to meet the challenges of food security and labor shortage. These machines replace a large amount of manual labor required in traditional agricultural production by integrating autonomous navigation technology. Autonomous navigation technology of unmanned agricultural machinery has been widely used in various agricultural production activities and has become one of the core technologies for achieving precision agriculture. In this field, path tracking control is a key link to improve the accuracy and stability of autonomous navigation systems of agricultural machinery. Therefore, developing efficient path tracking control strategies is crucial to enhance the tracking accuracy and robustness of agricultural machinery.

[0003] As a widely used robust control strategy for nonlinear uncertain systems, sliding mode control is favored for its simple implementation, rapid dynamic response and strong anti-interference ability. Many researchers choose sliding mode control to solve the path tracking problem of agricultural machinery.

[0004] However, most sliding mode control algorithms are usually first-order sliding mode algorithms. For traditional first-order sliding mode algorithms, the inevitable jitter phenomenon is a major problem. This phenomenon is not only harmful to the actuator in practical applications, but also may pose a challenge to the stability of the control system. Second-order sliding mode control can effectively reduce jitter, achieve finite time convergence, improve the accuracy and reliability of control, and support agricultural machinery to adapt to complex environments more quickly. At present, the second-order sliding mode control algorithm has been used to improve the path tracking accuracy of agricultural machinery, but because the influence of input delay is not considered, the tracking accuracy is significantly reduced in the case of large input signal delay. And because of the difficulty in measuring unknown delays, precise control of unmanned agricultural machinery is difficult to achieve. Summary of the invention

[0005] In view of the shortcomings in the prior art, the present invention provides a second-order sliding mode path tracking control method and system for unmanned agricultural machinery taking into account input delay, aiming to improve the path tracking accuracy of agricultural machinery under the influence of input delay, and ensure that agricultural machinery can achieve high-precision path tracking under complex actual operating conditions, thereby improving operating efficiency and making it more in line with actual application needs.

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

[0007] A second-order sliding mode path tracking control method for unmanned agricultural machinery considering input delay:

[0008] Design an input delay estimator to perform online estimation of unknown input delay:

[0009]

[0010] in, is the estimated value of the input delay estimator, τ is the actual value of the input delay, To control the error between the predicted delay and the actual delay of the input, is the error between the control input under the predicted delay and the artificially given delay, and ρ is a positive constant, ξ is a time constant, i.e. a given artificial delay;

[0011] Based on the input delay estimator, a compensation system suitable for unknown input delay is constructed:

[0012]

[0013] Where λ represents the compensation system, u(t) is the control input without input delay, p1 and b0 are positive constants, sign(λ) is the sign function, To predict delayed control input;

[0014] A new second-order sliding mode system without input delay is constructed by the compensation system. Combined with the compensation amount v of the second-order sliding mode controller, a new composite second-order sliding mode controller for unmanned agricultural machinery path tracking is designed to control the unmanned agricultural machinery in actual operation to track the desired path.

[0015] The novel composite second-order sliding mode controller is:

[0016] u(t)=-β2sign(|s2| 2α ·sign(s2)+β1|s1| α ·sign(s1))+v

[0017] Among them, α, β1 and β2 are positive constants, s1 represents the lateral deviation, and s2 represents the lateral deviation derivative compensated by the compensation system.

[0018] Furthermore, it also includes: based on the motion characteristics of the unmanned agricultural machinery, constructing a deviation dynamic model of lateral deviation and heading deviation including input delay characteristics, and defining state variables of the unmanned agricultural machinery path tracking process.

[0019] Furthermore, the deviation dynamic model of the lateral deviation and heading deviation including the input delay characteristics is:

[0020]

[0021] Among them, L e ,θe They represent the lateral deviation and heading deviation generated when the unmanned agricultural machinery tracks the expected path, V is the longitudinal speed of the unmanned agricultural machinery, δ is the direction parameter of the unmanned agricultural machinery, and L t is the wheelbase between the front and rear wheels of the unmanned agricultural machinery, c t is the radius of curvature of the desired path at time t, σ τ For the delayed control steering angle with input delay, u(t-τ) is the control input delayed by time τ based on the current time t.

[0022] Furthermore, the cost function of the input delay estimator is:

[0023] Furthermore, the novel second-order sliding mode system without input delay is:

[0024]

[0025] Among them, the lateral deviation s1=s=L e , the lateral deviation derivative compensated by the compensation system λ Error of second-order sliding mode controller under actual time delay and estimated time delay a(t, x) is a bounded function, specifically expressed as Where ω is the uncertainty in system modeling and is regarded as an unknown disturbance.

[0026] Furthermore, the controller compensation amount is:

[0027]

[0028] Where k is a positive constant and arctan(kλ) represents the inverse tangent function.

[0029] A second-order sliding mode path tracking control system for unmanned agricultural machinery considering input delay, comprising:

[0030] A host computer implements the control method and writes it into a processor unit;

[0031] The path planning unit is responsible for planning the ideal driving path for unmanned agricultural machinery;

[0032] Navigation and positioning system, used to continuously obtain real-time location information of unmanned agricultural machinery;

[0033] The communication unit is responsible for coordinating data communication between various components within the agricultural machinery;

[0034] The processor unit is responsible for collecting the state variables required by the control method and outputting the corresponding control instructions through the control method;

[0035] Vehicle control unit, responsible for executing instructions for agricultural machinery.

[0036] In the above technical solution, the host computer includes:

[0037] The second-order sliding mode control module is used to design a new composite second-order sliding mode controller to ensure that the lateral deviation and heading deviation of agricultural machinery converge quickly within a limited time in an environment with input delay;

[0038] An input delay estimator module, used for online estimation of unknown input delay;

[0039] Auxiliary compensation system module, used to compensate for the system control deviation caused by input delay, and to make real-time compensation adjustments to the second-order sliding mode control module under input delay conditions;

[0040] a deviation conversion module, which converts the difference between the current position coordinates of the agricultural machinery and the nearest predetermined path coordinate point into a lateral deviation and a heading deviation;

[0041] The signal delay processing module buffers and delays the collected signals to obtain a control signal with a given delay time.

[0042] The beneficial effects achieved by the present invention are:

[0043] 1. The present invention uses an input delay estimator to solve the problem that the unknown input delay is difficult to measure. The input delay estimator takes into account the discontinuity of the second-order controller, thereby avoiding the need to differentiate the controller and effectively solving the challenge of estimating unknown delays in the second-order sliding mode system.

[0044] 2. The present invention constructs an auxiliary compensation system suitable for unknown input delay through an input delay estimator, and constructs a new second-order sliding mode model through the auxiliary compensation system to adapt to the inherent input delay and uncertainty of the system, which helps to solve the path tracking problem of agricultural machinery with unknown input delay and uncertainty.

[0045] 3. The present invention uses second-order sliding mode control taking input delay into consideration, which not only offsets the adverse effects caused by unknown input delay, but also ensures the hardware safety of agricultural machinery and improves the tracking accuracy of unmanned agricultural machinery taking input delay into consideration. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a schematic diagram of the second-order sliding mode path tracking control of unmanned agricultural machinery considering input delay of the present invention;

[0047] Figure 2 A schematic diagram of the composition of the second-order sliding mode path tracking control device for unmanned agricultural machinery considering input delay of the present invention;

[0048] Figure 3 This is a schematic diagram of the structure of the second-order sliding mode path tracking control system for unmanned agricultural machinery considering input delay of the present invention;

[0049] Figure 4 The agricultural machinery path tracking curve diagram of the present invention;

[0050] Figure 5 A lateral deviation map for path tracking of agricultural machinery of the present invention;

[0051] Figure 6 A heading deviation map for path tracking of agricultural machinery of the present invention;

[0052] Figure 7 This is the unknown input delay estimation diagram of the agricultural machinery of the present invention. DETAILED DESCRIPTION

[0053] The present invention provides a second-order sliding mode path tracking control method and system for unmanned agricultural machinery considering input delay. The overall control scheme schematic diagram is shown in FIG. Figure 1 As shown. In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the technical solution in the example 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.

[0054] The second-order sliding mode path tracking control system of unmanned agricultural machinery considering input delay is composed as follows: Figure 2 As shown, it will be used to specifically illustrate the present invention, including the following parts:

[0055] The host computer realizes the writing and debugging of the control program of the present invention, writes the control algorithm into the processor unit through CAN communication, and records the working information of the agricultural machinery through real-time communication;

[0056] The path planning unit is responsible for planning the ideal driving path of the agricultural machinery and monitoring and displaying the current position of the agricultural machinery in real time;

[0057] Navigation and positioning system, used to continuously obtain real-time location information of agricultural machinery;

[0058] The communication unit is responsible for coordinating data communication between various components within the agricultural machinery, including receiving and sending key data;

[0059] The processor unit is responsible for collecting relevant state variable data required by the control program, calculating and outputting corresponding control instructions through the control program;

[0060] The vehicle control unit is responsible for executing the instructions of the agricultural machinery and managing the forward and steering movements of the machinery.

[0061] For the embodiment of the above system, the host computer includes the following modules: Figure 3 As shown:

[0062] The second-order sliding mode control module is responsible for ensuring that the lateral deviation and heading deviation of the agricultural machinery can converge quickly within a limited time in an environment with input delay, so as to achieve efficient and rapid tracking of the unmanned agricultural machinery on the predetermined path;

[0063] The input delay estimator module is used to solve the problem that the unknown input delay is difficult to measure and the input delay estimation accuracy is required to be high;

[0064] Auxiliary compensation system module, used to compensate for the system control deviation caused by input delay, and ensure real-time compensation adjustment of the second-order sliding mode controller under input delay conditions through adaptive mechanism;

[0065] The deviation conversion module is responsible for converting the difference between the current position coordinates of the agricultural machinery and the nearest predetermined path coordinate point into lateral deviation and heading deviation;

[0066] The signal delay processing module buffers and delays the collected signals to obtain a control signal with a given delay time.

[0067] For the embodiment of the above system, an embodiment of a second-order sliding mode path tracking control method for an unmanned agricultural machine taking into account input delay includes the following steps:

[0068] S1, based on the motion characteristics of unmanned agricultural machinery, a deviation dynamic model of lateral deviation and heading deviation including input delay characteristics is constructed, and the state variables related to the agricultural machinery path tracking process are defined;

[0069] Specifically, in this example, the tracking deviation dynamic model of unmanned agricultural machinery with input signal delay is:

[0070]

[0071] Among them, V is the longitudinal speed of the unmanned agricultural machinery, δ is the directional parameter of the unmanned agricultural machinery, and L t is the wheelbase between the front and rear wheels of the unmanned agricultural machinery, c t is the radius of curvature of the desired path at time t, L e ,θ e They represent the lateral deviation and heading deviation generated when the unmanned agricultural machinery tracks the expected path, σ τ represents the delayed control steering angle with input delay, and u(t-τ) is the control input delayed by time τ based on the current time t.

[0072] S2, since the actual control input is affected by the unknown input delay, an input delay estimator is designed using negative gradient optimization technology to quickly and accurately estimate the unknown input delay online. Real-time input delay estimation can effectively deal with the unknown input delay problem of unmanned agricultural machinery in a changing environment and ensure the effectiveness of the controller;

[0073] Negative gradient optimization is used to estimate the unknown input delay. The cost function uses the controller deviation as an indicator and has the following form:

[0074]

[0075] in, is the cost function, is the estimated value of the input delay estimator, τ is the actual value of the input delay, Represents the square of the error between the predicted delay and the actual delay of the control input.

[0076] The innovation of the cost function design lies in that it is not feasible to directly measure the input delay in the actual system, and the traditional cost function based on the input delay estimation error cannot be constructed. Therefore, the input delay estimation problem becomes difficult to handle, and the unmeasurable error Compared with Easier to obtain.

[0077] The input delay estimator is specifically:

[0078]

[0079] in, To control the error between the predicted delay and the actual delay of the input, it is specifically expressed as Represents the error of the control input under the predicted delay and the artificially given delay, which is specifically expressed as ρ is a positive constant selected empirically, and ξ is a time constant not less than the control period, that is, a given artificial delay.

[0080] The innovation of this input delay estimator is that it can accurately estimate the unknown input delay, the convergence speed can be adjusted by the parameter ρ, and it can be applied to discontinuous controllers such as second-order sliding mode, which makes it more applicable in practical engineering.

[0081] S3, based on the input delay estimator, construct a compensation system suitable for unknown input delay, the compensation system can realize adaptive adjustment and offset the control deviation caused by the controller input delay in real time; the compensation system is specifically:

[0082]

[0083] Where λ represents the compensation system, u(t) is the control input without input delay, p1 and b0 are positive constants, and the sign function sign(λ) is specifically expressed as:

[0084]

[0085] The innovation of this compensation system is that it uses the estimated value of input delay to avoid the problem of unknown input delay. This compensation system can be dynamically adjusted according to the controller deviation, compensating the control error of the system and shortening the convergence time.

[0086] S4, a new second-order sliding mode system without input delay is constructed through the compensation system, which has the following form:

[0087]

[0088] Where, s1=s=L e , represents the lateral deviation; Indicates the lateral deviation derivative that has been compensated by the compensation system; represents the error of the second-order sliding mode controller under the actual delay and estimated delay; a(t, x) is a bounded function, which is specifically expressed as Where ω is the uncertainty in system modeling and is regarded as an unknown disturbance.

[0089] The innovation of the new second-order sliding mode system design is that the delay-free expression of the system is obtained by introducing a compensation system, which solves the problem of difficult design of real-time controllers. The design of the second-order sliding mode system also simplifies the conditions of the system uncertainties, and has more advantages in verification conditions and parameter selection.

[0090] S5, design the compensation v of the second-order sliding mode controller, which has the following form:

[0091]

[0092] Where k is a positive constant selected empirically, and the function arctan(kλ) represents the inverse tangent function.

[0093] The innovation of the controller compensation is that by introducing an auxiliary system, the control law with input delay can be brought close to the actual control law. On the one hand, for agricultural machinery, it can effectively alleviate the deviation problem caused by the input signal delay of agricultural machinery. On the other hand, for unknown input delay, the designed auxiliary system solves the problem of difficulty in effectively compensating the controller under unknown input conditions.

[0094] S6, based on S4 and S5, designs a new composite second-order sliding mode controller for unmanned agricultural machinery path tracking through the power integral method, so that agricultural machinery can quickly and accurately track the desired path. The new composite second-order sliding mode controller is a real-time controller without time delay and has the following form:

[0095] u(t)=-β2sign(|s2| 2α ·sign(s2)+β1|s1| α ·sign(s1))+v (7)

[0096] Among them, β1 and β2 are normal numbers, and the normal number α satisfies the condition α≥1.

[0097] The new composite second-order sliding mode controller can ensure the stability of agricultural machinery within a limited time. It can ensure high-precision tracking effect in the case of input delay, and can further ensure ideal second-order sliding mode tracking effect in the case of no input delay.

[0098] An embodiment of a second-order sliding mode path tracking control method and system for unmanned agricultural machinery considering input delay 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.

[0099] In order to verify that the present invention has excellent tracking accuracy, the initial lateral deviation of the unmanned agricultural machinery is set to 100 cm, and the unknown input delay is 50 ms, and the tracking accuracy of the embodiment is tested based on the path tracking performance. The experimental results are shown in Figure 2. Figure 4-Figure 7 As shown, it is not difficult to see that the control accuracy of this embodiment in the experiment is higher, and the control method tracks the reference path more effectively under the existence of input delay, and the estimation performance of the input delay estimator is also very good, 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.

[0100] 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.

[0101] 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 second-order sliding mode path tracking control method for unmanned agricultural machinery considering input delay, characterized in that: Design an input delay estimator to perform online estimation of unknown input delay: in, is the estimated value of the input delay estimator, τ is the actual value of the input delay, To control the error between the predicted delay and the actual delay of the input, is the error between the control input under the predicted delay and the artificially given delay, and ρ is a positive constant, ξ is a time constant, i.e. a given artificial delay; Based on the input delay estimator, a compensation system suitable for unknown input delay is constructed: Where λ represents the compensation system, u(t) is the control input without input delay, p1 and b0 are positive constants, sign(λ) is the sign function, To predict delayed control input; A new second-order sliding mode system without input delay is constructed by the compensation system. Combined with the compensation amount v of the second-order sliding mode controller, a new composite second-order sliding mode controller for unmanned agricultural machinery path tracking is designed to control the unmanned agricultural machinery in actual operation to track the desired path. The novel composite second-order sliding mode controller is: u(t)=-β2sign(|s2| 2α ·sign(s2)+β1|s1| α ·sign(s1))+v Among them, α, β1 and β2 are positive constants, s1 represents the lateral deviation, and s2 represents the lateral deviation derivative compensated by the compensation system.

2. The second-order sliding mode path tracking control method for unmanned agricultural machinery considering input delay according to claim 1 is characterized in that: It also includes: based on the motion characteristics of the unmanned agricultural machinery, constructing a deviation dynamic model of the lateral deviation and heading deviation including input delay characteristics, and defining the state variables of the unmanned agricultural machinery path tracking process.

3. The second-order sliding mode path tracking control method for unmanned agricultural machinery considering input delay according to claim 2 is characterized in that: The deviation dynamic model of the lateral deviation and heading deviation including the input delay characteristics is: Among them, L e ,θ e They represent the lateral deviation and heading deviation generated when the unmanned agricultural machinery tracks the expected path, V is the longitudinal speed of the unmanned agricultural machinery, δ is the direction parameter of the unmanned agricultural machinery, and L t is the wheelbase between the front and rear wheels of the unmanned agricultural machinery, c t is the radius of curvature of the desired path at time t, σ τ For the delayed control steering angle with input delay, u(t-τ) is the control input delayed by time τ based on the current time t.

4. The second-order sliding mode path tracking control method for unmanned agricultural machinery considering input delay according to claim 3 is characterized in that: The cost function of the input delay estimator is:

5. The second-order sliding mode path tracking control method for unmanned agricultural machinery considering input delay according to claim 3 is characterized in that: The novel second-order sliding mode system without input delay is: Among them, the lateral deviation s1=s=L e , the lateral deviation derivative compensated by the compensation system λ Error of second-order sliding mode controller under actual time delay and estimated time delay a(t, x) is a bounded function, specifically expressed as Where ω is the uncertainty in system modeling and is regarded as an unknown disturbance.

6. The second-order sliding mode path tracking control method for unmanned agricultural machinery considering input delay according to claim 1 is characterized in that: The controller compensation amount is: Where k is a positive constant and arctan(kλ) represents the inverse tangent function.

7. A system for implementing the second-order sliding mode path tracking control method for unmanned agricultural machinery considering input delay as described in any one of claims 1 to 6, characterized in that: include: A host computer implements the control method and writes it into a processor unit; The path planning unit is responsible for planning the ideal driving path for unmanned agricultural machinery; Navigation and positioning system, used to continuously obtain real-time location information of unmanned agricultural machinery; The communication unit is responsible for coordinating data communication between various components within the agricultural machinery; The processor unit is responsible for collecting the state variables required by the control method and outputting the corresponding control instructions through the control method; Vehicle control unit, responsible for executing instructions for agricultural machinery.

8. The system according to claim 7, characterized in that The host computer comprises: The second-order sliding mode control module is used to design a new composite second-order sliding mode controller to ensure that the lateral deviation and heading deviation of agricultural machinery converge quickly within a limited time in an environment with input delay; An input delay estimator module, used for online estimation of unknown input delay; Auxiliary compensation system module, used to compensate for the system control deviation caused by input delay, and to make real-time compensation adjustments to the second-order sliding mode control module under input delay conditions; a deviation conversion module, which converts the difference between the current position coordinates of the agricultural machinery and the nearest predetermined path coordinate point into a lateral deviation and a heading deviation; The signal delay processing module buffers and delays the collected signals to obtain a control signal with a given delay time.

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