A tractor front wheel steering control method with strong anti-interference

Abstract

This invention discloses a tractor front wheel steering control method with strong anti-disturbance capability, comprising the following steps: (1) using the steering system identification model P m Signal synthesizers 2 and 3 are equipped with a time-delay processing module D(s), wherein the steering system identification model consists of a non-time-delay component P. m0 The steering system identification model is connected in series with the time-delay part. The output of the steering system identification model and the actual front wheel angle feedback y(s) are synthesized in reverse in the signal synthesizer three, and then combined with the non-time-delay part P of the steering system identification model. m0 The output of the signal is synthesized in the second signal synthesizer, and the generated signal y is used as an input of the state observer O(s); (2) the signal is obtained by the signal synthesis method, where u is the output of the front wheel steering angle tracking controller K(s), P0 is the non-time-delay part of the steering system P(s), and e ‑θs This represents the time delay component in the steering system P(s). This method involves less computation in the control process, provides fast and accurate tracking of the desired front wheel angle, and exhibits strong anti-interference capabilities, thus improving the steering control performance of automated driving tractors.

Description

Technical Field

[0001] This invention relates to the field of tractor automatic driving, and more specifically, to a tractor front wheel steering control method with strong anti-disturbance capabilities. Background Technology

[0002] With the rapid increase in agricultural labor costs, the demand for agricultural machinery automation is becoming increasingly apparent. Automatic driving technology for agricultural machinery is one of the most important supporting technologies for modern agricultural equipment. It can reduce reliance on manual labor, improve product quality, and lower production costs. Precise path tracking is the primary function of automatic driving agricultural machinery, and automatic steering control is one of the most effective means to achieve precise path tracking. Typically, the automatic steering system executes steering commands sent by the host computer to achieve path tracking. In most cases, the host computer sends the steering angle obtained through navigation algorithms to the automatic steering system. Therefore, precise and stable steering angle control is of great significance for the promotion and application of automatic driving technology.

[0003] Currently, steering mechanisms used for automatic tractor operation mainly employ two forms: proportional electromagnetic hydraulic valves and motor-controlled steering. For example, patent application CN202210586527 discloses a wheel-side electric tractor steering control method, designing an electro-hydraulic drive steering module and four wheel-side motor control modules to achieve five steering modes for the tractor. Patent application CN201810117103 discloses a hydraulic steering control system and method for agricultural wheeled tractors, mainly involving the structure and working principle of the steering system. Patent application CN202210877235 discloses a tractor hydraulic system and steering control method with bidirectional driving function, achieving bidirectional driving functionality by adding electromagnetic reversing valves, differential lock control valves, hydraulic pumps, and flow divider valves to the existing tractor steering system.

[0004] The common drawback of the aforementioned existing technologies is that changes in the working environment and steering load during tractor operation can cause disturbances to the steering control. When the steering system is disturbed, it is prone to oscillation and divergence. The control methods of the aforementioned existing technologies are difficult to overcome the impact of disturbances on steering accuracy.

[0005] To address the disturbance problem, invention patent application number 201611103825.1 discloses a hydraulic steering control system and method for tractor navigation, which designs a voltage servo controller and an anti-disturbance controller for the hydraulic steering system. However, the method in this patent only suppresses small-amplitude disturbances in the system, and when disturbances occur, the steering control system exhibits significant fluctuations in its tracking of the set front wheel angle.

[0006] In other words, none of the existing technologies mentioned above can better solve the disturbance problem, and under the premise of ensuring the accuracy and speed of steering control, greatly reduce the impact of disturbance on the front wheel steering performance, and improve the stability and reliability of steering control when the autonomous tractor is operating in the field. Summary of the Invention

[0007] The technical problem to be solved by this invention is to address the delay and disturbance phenomena existing in the front wheel steering system of a tractor, and to provide a tractor front wheel steering control method with strong anti-disturbance capabilities. While ensuring the accuracy and speed of steering control, it greatly reduces the impact of disturbances on the front wheel steering performance, and improves the stability and reliability of steering control when the autonomous tractor is operating in the field.

[0008] The present invention achieves its objective by employing the following technical solution:

[0009] A tractor front wheel steering control method with strong anti-interference capabilities includes the following steps:

[0010] (1) Using the steering system identification model P m Signal synthesizers 2 and 3 are equipped with a time-delay processing module D(s), wherein the steering system identification model consists of a non-time-delay component P. m0 and time delay part The steering system identification model is connected in series. The output of the steering system identification model and the actual front wheel angle feedback y(s) are synthesized in reverse in the signal synthesizer three, and then combined with the non-time-delay part P of the steering system identification model. m0 The output of is synthesized in signal synthesizer 2, and the generated signal y' is used as an input to the state observer O(s); (2) the signal is obtained through signal synthesis method. Where u is the output of the front wheel steering angle tracking controller K(s), P0 is the non-time-delay part of the steering system P(s), and e -θs This refers to the time-delay component in the steering system P(s).

[0011] The input terminals of signal synthesizer 1 are connected to the desired front wheel angle r(s) and one output terminal of state observer O(s), respectively. The two input terminals of front wheel steering angle tracking controller K(s) are connected to the output terminal of signal synthesizer 1 and the other output terminal of state observer O(s), respectively. The output terminal of front wheel steering angle tracking controller K(s) is connected to one input terminal of state observer O(s), one input terminal of time delay processing module D(s), and one input terminal of steering system P(s), respectively. The output terminal of steering system P(s) is connected to the input terminal of actual front wheel angle feedback y(s). The other input terminal of time delay processing module D(s) is connected to the output terminal of actual front wheel angle feedback y(s), respectively. The two input terminals of state observer O(s) are connected to the output terminal of time delay processing module D(s) and the output terminal of front wheel steering angle tracking controller K(s), respectively.

[0012] As a further improvement to this technical solution:

[0013] The state observer O(s) takes the delay-free output y' and the front wheel steering angle tracking controller output u as inputs to estimate the delay-free actual front wheel angle y' and to estimate the uncertainties, disturbances, and reference changes in the system. The estimated quantities are obtained using a linear state observer design method. and f.

[0014] (1) Based on the identified tractor steering system model P m (s)=Ke -θs / (s(Ts+1)), where K is the model gain and T is the time constant, we obtain K = 18.56, T = 0.93, and θ = 0.15 through identification. The state-space expression of the steering system model is as follows:

[0015]

[0016] Where x1 represents the front wheel steering angle, x2 represents the front wheel steering speed, b = K / T, f = -x2 / K can be further extended to represent the overall disturbance in the system, and y is the measurable front wheel steering angle in the system.

[0017] (2) Design the state observer O(s)

[0018]

[0019] z1 and z2 are estimates of x1 and x2, z3 is an estimate of the generalized uncertainty function f, ω is the bandwidth of the observer, and β i (i = 1, 2, 3) is the observer gain, determined by β. i =((1+n)!) / ((1+ni)!i!),1≤i≤n+1,n=2, we can get β1=3,β2=3,β3=1. It is an estimate of the output y' of the time delay processing module.

[0020] As a further limitation of this technical solution, the front wheel steering angle tracking controller K(s) is obtained through a simple sliding mode theory method:

[0021] (1) In signal synthesizer one, the desired front wheel angle r(s) and the estimated value are used. As for the tractor's steering angle control error

[0022] (2) Establishing a linear sliding surface

[0023] (3) Obtain the output of the front wheel steering angle tracking controller K(s):

[0024]

[0025] Solving the above expression, we obtain the control law of the steering system as follows:

[0026]

[0027] Where λ is the gradient of the sliding surface, which is an adjustable parameter; r is the desired front wheel angle; k is the adjustable sliding controller parameter; ε is the sliding switching coefficient; and δ is a normal number with a very small amplitude.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. The tractor front wheel steering control method designed in this invention can reduce the impact of time delay during the control process by estimating the front wheel steering angle without time delay. It introduces a state observer to estimate unknown disturbances and system state. The use of sliding mode control not only improves the servo performance of the system, but also improves the disturbance suppression capability of the system.

[0030] 2. This invention proposes a tractor front wheel steering control method with strong anti-interference capabilities. It is applicable not only to tractor front wheel steering control systems based on hydraulic steering, but also to all first-order and second-order time-delay control objects, demonstrating strong universality. This method not only strongly suppresses sudden disturbances in the system, but also has a significant suppression effect on white noise-like interference.

[0031] 3. The tractor front wheel steering control method designed in this invention has strong anti-interference capabilities. The algorithm is simple and the amount of computation is small. It is very suitable for automatic navigation control slave computers with limited hardware resources and high requirements for control response. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the tractor front wheel steering control method with strong anti-interference capability designed for this invention.

[0033] Figure 2 This is a block diagram of a tractor front wheel steering control system with strong anti-interference capabilities, as given in an embodiment of the present invention.

[0034] Figure 3 This is a diagram illustrating the tracking effect of the actual front wheel angle on the sinusoidal desired front wheel angle according to the present invention.

[0035] Figure 4 This diagram illustrates the suppression effect of the control method of the present invention on step interference signals.

[0036] Figure 5 This diagram illustrates the suppression effect of the control method of the present invention on white noise interference signals.

[0037] Figure 6 This diagram illustrates the suppression effect of the control method of the present invention on step interference signals under parameter perturbation. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are merely illustrative and not intended to limit the invention. This invention covers any substitutions, modifications, or equivalent methods and solutions made within the spirit and scope of the invention as defined by the claims. To provide a better understanding of this invention, specific details are described in detail in the specific embodiments; parts not described are conventional techniques in the art.

[0039] refer to Figure 1 - Figure 2 The present invention provides a tractor front wheel steering control method with strong anti-interference capability, comprising the following steps:

[0040] (1) Using the steering system identification model P m Signal synthesizers 2 and 3 are equipped with a time-delay processing module D(s), wherein the steering system identification model consists of a non-time-delay component P. m0 and time delay part The steering system identification model is connected in series. The output of the steering system identification model and the actual front wheel angle feedback y(s) are synthesized in reverse in the signal synthesizer three, and then combined with the non-time-delay part P of the steering system identification model. m0 The output of is synthesized in signal synthesizer 2, and the generated signal y' is used as an input to the state observer O(s); (2) the signal is obtained through signal synthesis method. Where u is the output of the front wheel steering angle tracking controller K(s), P0 is the non-time-delay part of the steering system P(s), and e -θs This refers to the time-delay component in the steering system P(s).

[0041] The input terminals of signal synthesizer 1 are connected to the desired front wheel angle r(s) and one output terminal of state observer O(s), respectively. The two input terminals of front wheel steering angle tracking controller K(s) are connected to the output terminal of signal synthesizer 1 and the other output terminal of state observer O(s), respectively. The output terminal of front wheel steering angle tracking controller K(s) is connected to one input terminal of state observer O(s), one input terminal of time delay processing module D(s), and one input terminal of steering system P(s), respectively. The output terminal of steering system P(s) is connected to the input terminal of actual front wheel angle feedback y(s). The other input terminal of time delay processing module D(s) is connected to the output terminal of actual front wheel angle feedback y(s), respectively. The two input terminals of state observer O(s) are connected to the output terminal of time delay processing module D(s) and the output terminal of front wheel steering angle tracking controller K(s), respectively.

[0042] The state observer O(s) takes the zero-delay output y' and the output u of the front wheel steering angle tracking controller as inputs to estimate the zero-delay actual front wheel angle y' and to estimate the uncertainties, disturbances, and reference changes in the system. The estimated values ​​are obtained using a linear state observer design method. and f.

[0043] (1) Based on the identified tractor steering system model P m (s)=Ke -θs / (s(Ts+1)), where K is the model gain and T is the time constant. Through identification, K = 18.56, T = 0.93, and θ = 0.15. Write the state-space expression for the steering system model.

[0044]

[0045] x1 represents the front wheel steering angle, x2 represents the front wheel steering speed, b = K / T, f = -x2 / K can be further extended to represent the overall disturbance in the system, and y is the measurable front wheel steering angle in the system.

[0046] (2) Design the state observer O(s)

[0047]

[0048] Where z1 and z2 are estimates of x1 and x2, z3 is an estimate of the generalized uncertainty function f, ω is the bandwidth of the observer, and β is the bandwidth of the observer. i (i = 1, 2, 3) is the observer gain, determined by β. i =((1+n)!) / ((1+ni)!i!),1≤i≤n+1,n=2, we can get β1=3,β2=3,β3=1. It is an estimate of the output y' of the time delay processing module.

[0049] The front wheel steering angle tracking controller K(s) is obtained through a simple sliding mode theory method:

[0050] (1) In signal synthesizer one, the desired front wheel angle r(s) and the estimated value are used. As for the tractor's steering angle control error

[0051] (2) Establishing a linear sliding surface

[0052] (3) The output of the front wheel steering angle tracking controller K(s) is as follows:

[0053]

[0054] Solving the above expression, we obtain the control law of the steering system as follows:

[0055]

[0056] Where λ is the gradient of the sliding surface, which is an adjustable parameter; r is the desired front wheel angle; k is the adjustable sliding controller parameter; ε is the sliding switching coefficient; and δ is a normal number with a very small amplitude.

[0057] Based on the steering system model obtained from this identification, the parameters for the state observer and sliding mode controller are selected as follows: λ = 10, k = 1.5, ε = 0.001, δ = 0.001, ω = 67.

[0058] See Figure 2 A control system based on hydraulic drive, which is a tractor front wheel steering control method with strong anti-interference capabilities. It includes a microcontroller, a DA conversion module, solenoid valves, a power supply module, a steering system, and a steering angle sensor.

[0059] The power module provides operating voltage for the microcontroller and DA conversion module. The microcontroller receives the desired front wheel angle r(s) through serial communication with the navigation control system, and uses the DA conversion module to generate a voltage in the range of -5V to +5V to control the solenoid valve. An angle sensor is used to detect the front wheel angle of the tractor to realize the actual front wheel angle feedback y(s).

[0060] During the operation of the steering control system, the microcontroller receives the desired front wheel angle r(s) from the navigation control system in real time and obtains the actual front wheel angle feedback y(s) through the steering angle sensor. The microcontroller executes a strong disturbance rejection front wheel steering control method program, generating a control quantity u. The control quantity u is converted into a corresponding control voltage by the DA conversion module and acts on the solenoid valve. By controlling the opening degree and direction of the solenoid valve, the flow rate and direction of the steering fluid are controlled, driving the rotation of the steering torsion bar and thus changing the front wheel angle of the tractor. The entire process is repeated until the actual front wheel angle of the tractor reaches the control requirement.

[0061] The control system designed using the above method was simulated using the SIMULINKL component in MATLAB software. The simulation results were compared with the method described in the invention patent application number 201611103825.1, where the two controllers are designed as follows:

[0062] C(S)=3.7581(1+1.6667 / s+0.1857s), L(S)=1 / (0.1114s 2 +0.6s+1)

[0063] D(S)=0.2542(1+0.5702 / s+0.4811s)(1+0.075s) / (1+0.123s)

[0064] First, to verify the tracking accuracy and speed of the control method for the desired steering angle, the desired front wheel angle r(s) was set as a sinusoidal signal with a period of 10s and an amplitude of 1. The actual front wheel steering angle control effects of the two control methods are as follows: Figure 3 As shown. In this invention, the output angle is represented by a solid line, while in the invention patent application number 201611103825.1, the output angle is represented by a dashed line. Figure 3 It can be seen that both methods can accurately and quickly track the desired front wheel angle r(s). To verify the anti-interference capability of the control method, a step signal was used as the desired front wheel angle. Step noise with an amplitude of -0.5 and white noise with a noise power of 0.01 and a sampling time of 0.01s were introduced into the system, respectively. The system tracking control effect in the two cases is as follows: Figure 4 and Figure 5 As shown, it is evident that the method of this invention has a strong suppression effect on disturbances, and the impact of the disturbance on the actual front wheel angle is minimal. Furthermore, assuming that during the tracking of the desired step front wheel angle, both a step disturbance and a steering system parameter perturbation (K=30) exist simultaneously in the system, the actual front wheel angle y(s) under the action of the two methods is as follows: Figure 6 As shown, it can be seen that even when the model parameters are mismatched, the method proposed in this invention still exhibits strong anti-disturbance ability and strong robustness.

[0065] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A tractor front wheel steering control method with strong anti-interference capability, characterized in that, Includes the following steps: (1) Identification model using steering system P m 、 Signal synthesizers two and three are equipped with a time-delay processing module D(s), wherein the steering system identification model consists of a non-time-delay component. P m0 and time delay part The steering system identification model is connected in series. The output of the steering system identification model and the actual front wheel angle feedback y(s) are synthesized in reverse in the signal synthesizer three, and then combined with the non-time-delay part of the steering system identification model. P m0 The output of the signal is synthesized in signal synthesizer two, and the generated signal... As an input to the state observer O(s); (2) Obtained through signal synthesis method ,in u The output of the front wheel steering angle tracking controller K(s) P 0 For steering system P(s) The non-time-delay part; This refers to the time-delay component in the steering system P(s); The state observer O(s) outputs without delay. and front wheel steering angle tracking controller output u As input, the actual front wheel angle without delay Estimation is performed to account for uncertainties, disturbances, and reference variations in the system. A linear state observer design method is used to obtain the estimators. and ; (3) Based on the identified tractor steering system model K is the model gain, and T is the time constant, both of which are obtained through identification: The state-space expression of the steering system model is as follows: ； x 1 Indicates the front wheel steering angle. x 2 Indicates the steering speed of the front wheels. Further, this represents the overall disturbance present in the system. The measurable front wheel steering angle in the system; (4) Design the state observer : ； z 1, z 2 Yes x 1 ,x 2 The estimate, z 3 For generalized uncertain functions The estimate, For the bandwidth of the observer, For observer gain, Output of the time delay processing module The estimate; (5) The front wheel steering angle tracking controller K(s) is obtained through a simple sliding mode theory method, including the following steps: 1) In signal synthesizer one, the desired front wheel angle r(s) and the estimated value are used. As for the tractor's steering angle control error ; 2) Establish a linear sliding surface ; 3) Obtain the output of the front wheel steering angle tracking controller K(s): ； (6) Solving the above expression, we obtain the control law of the steering system as follows: ； in, is the gradient of the sliding surface, is an adjustable parameter; r is the desired front wheel angle; k is an adjustable sliding mode controller parameter; This is the sliding mode switching coefficient. For positive integers, .

Images