A double PID tracking control method suitable for front and rear axle independent steering AGV

Abstract

The application discloses a tracking control technology field related to automatic driving, and particularly discloses a double-PID tracking control method for front-rear axle independent steering AGV, AGV vehicles are front axle of front wheels and rear axle of rear wheels which can be independently controlled, the tracking control method includes straight path tracking control recorded as straight line mode and / or turning path tracking control recorded as turning mode, the tracking control execution of the straight line mode or the turning mode includes tracking control of the front wheels and the rear wheels, since the front wheels and the rear wheels can be independently controlled, the tracking control method is consistent with the tracking control execution of the front wheels and the tracking control execution of the rear wheels. The method is an implementation method of tracking control on a path composed of a straight line and a circular arc for a chassis model with independent steering of front and rear wheels and without original rotation.

Description

Technical Field

[0001] The present invention relates to the technical field of tracking control for autonomous driving. Background Art

[0002] Tracking control technology for autonomous driving refers to the technology used to implement vehicle tracking and control within autonomous driving systems. It is a critical component of autonomous driving systems, ensuring that the vehicle accurately follows its chosen path and controls itself based on real-time environmental and sensor data for safe, stable, and efficient driving. Tracking control technology uses control algorithms to calculate vehicle control commands to achieve the desired trajectory. Common control algorithms include PID control and model predictive control (MPC). MPC uses vehicle dynamics and environmental models to predict vehicle behavior over a period of time and implements control based on the predicted results to achieve more accurate tracking. Tracking control technology requires real-time control and adjustments based on vehicle status and environmental changes. By collecting and processing sensor data in real time, the tracking control system continuously updates vehicle status and environmental information and adjusts control commands based on this feedback to achieve precise tracking. In general, using the appropriate tracking control algorithm for the specific scenario and vehicle can maximize the algorithm's performance and achieve optimal control results.

[0003] Existing tracking control technologies primarily target differential chassis models. Few control methods exist for chassis models with independent front and rear wheel steering and no rotational capability. Furthermore, existing PID tracking control methods exhibit large tracking errors in cornering scenarios. This invention addresses these limitations by proposing a method for tracking control along a path composed of straight lines and circular arcs for a chassis model with independent front and rear wheel steering and no rotational capability. Summary of the Invention

[0004] The purpose of the present invention is to provide a dual PID tracking control method suitable for AGVs with independent steering of the front and rear axles. In view of the above limitations, a method for implementing tracking control on a path composed of straight lines and circular arcs is proposed for a chassis model with independent steering of the front and rear wheels and non-rotatable in situ.

[0005] To achieve the above-mentioned purpose, the technical solution of the present invention is: a dual PID tracking control method suitable for AGVs with independent front and rear axle steering, wherein the front axle of the front wheels and the rear axle of the rear wheels of the AGV vehicle can be independently steered and controlled respectively. The tracking control method includes tracking control of a straight path recorded as a straight mode and / or tracking control of a turning path recorded as a turning mode. The tracking control execution of the straight mode or the turning mode includes tracking control of the front wheels and the rear wheels. Since the front wheels and the rear wheels can be independently steered and controlled respectively, the tracking control method is described by taking the tracking control execution of the front wheels as an example. The execution method steps of the rear wheels can be obtained by referring to the front wheels. The steps of the front wheel tracking control method in the straight mode and / or the turning mode are as follows:

[0006] Straight line mode:

[0007] 1) Obtain magnetic navigation positioning;

[0008] 2) The given linear speed is a fixed value;

[0009] 3) Calculate the lateral offset error, cumulative lateral offset error, and heading error from the front axle center of the front wheel to the arc path;

[0010] 4) Determine the PID coefficient and calculate the dynamic front wheel deflection angle value corresponding to the PID;

[0011] 5) Determine the final front wheel deflection angle value;

[0012] 6) The calculated final front wheel deflection angle w is output to the controller as the actual control value, controlling the front wheel to deflect according to the set value;

[0013] 7) Return to step 2) and repeat the calculation cycle to achieve PID tracking control of the vehicle's front wheels;

[0014] Turning Mode:

[0015] S1) Obtain magnetic navigation positioning;

[0016] S2) The given linear speed is a fixed value;

[0017] S3) calculating the lateral offset error, cumulative lateral offset error, and heading error from the center of the front axle of the front wheel to the arc path;

[0018] S4) determining the PID coefficient and calculating the dynamic front wheel deflection angle value corresponding to the PID;

[0019] S5) determining a static deflection angle value corresponding to the front tire;

[0020] S6) determining a final front wheel deflection angle value;

[0021] S7) outputting the calculated final front wheel deflection angle w as the actual control value to the controller to control the front wheel to deflect according to the set value;

[0022] S8) Return to step 2) and perform calculation in a loop.

[0023] In the straight line mode:

[0024] Step 3) is this:

[0025] Through steps 1) and 2), first, calculate the lateral offset error of the front wheel from the center of the front axle to the arc path and record it as , and the lateral error is set to positive when the front wheel is outside the path, and negative when the front wheel is inside the path;

[0026] Next, calculate the cumulative lateral offset error and record it as , the cumulative lateral offset error is the cumulative sum of the lateral offset errors calculated from the starting time to the current time;

[0027] Then, the heading error is calculated as , with counterclockwise as positive, the heading error is the front wheel heading and is recorded as and the reference heading is recorded as The difference, that is , where the reference heading is the corresponding tangent direction of the front wheel at the nearest point on the arc;

[0028] Step 4) is to calculate the lateral error in step 3) , cumulative lateral error and heading error After that, the PID parameters are determined through debugging and the corresponding dynamic front wheel deflection angle is obtained. .

[0029] Step 5) is as follows, the final front wheel deflection angle used for control is recorded as , the dynamic front wheel deflection angle obtained by step 4) As the final front wheel deflection angle value used for control, that is .

[0030] In the turning mode:

[0031] Step S3) is as follows:

[0032] Through step S1) and step S2), first, calculate the lateral offset error of the front wheel from the center of the front axle to the arc path and record it as , and the lateral error is set to positive when the front wheel is outside the path, and negative when the front wheel is inside the path;

[0033] Next, calculate the cumulative lateral offset error and record it as , the cumulative lateral offset error is the cumulative sum of the lateral offset errors calculated from the starting time to the current time;

[0034] Then, the heading error is calculated as , with counterclockwise as positive, the heading error is the front wheel heading and is recorded as and the reference heading is recorded as The difference, that is , where the reference heading is the corresponding tangent direction of the front wheel at the nearest point on the arc;

[0035] Step S4) is to calculate the lateral error in step S3) , cumulative lateral error and heading error After that, the PID parameters are determined through debugging, and the corresponding dynamic front wheel deflection angle is recorded as ,

[0036] ;

[0037] Step S5) is based on the wheelbase The turning radius is recorded as R, and the static deflection angle value corresponding to the front tire is recorded as ,

[0038] ;

[0039] Step 6) is to calculate the final front wheel deflection angle used for control based on the dynamic front wheel deflection angle and the static front wheel deflection angle: .

[0040] The AGV vehicle is provided with a magnetic sensor at the center of the front axle of the front wheel and the center of the rear axle of the rear wheel, respectively, and the two magnetic sensors respectively sense the magnetic nails on the path; in step 1) and / or step S1), the magnetic navigation positioning of the two magnetic sensors is obtained; in step 3) and / or step S3), when the two magnetic sensors sense the magnetic nails at the same time, the true value of the lateral error obtained by direct sensing by the magnetic sensors is used as the correction value instead of the lateral offset error for calculation; when the two magnetic sensors do not sense the magnetic nails at the same time, the sensor data of the odometer or inertial measurement unit is obtained to calculate the lateral offset error based on the latest correction value.

[0041] AGV vehicles use different modes for control in different sections of the road. They use straight line mode control in straight sections and turning mode control in arc sections. They automatically switch modes at the connection points between straight sections and arc sections.

[0042] The rules for switching modes are as follows: taking the center of the line connecting the front and rear wheel axles of the vehicle as the reference point, the driving trajectory of the reference point is formed by connecting a straight line and an arc. Taking starting from a straight section as an example, starting from the straight section, it is controlled in a straight line mode; when the reference point runs to the connection point of the straight line trajectory and the circular arc trajectory, it switches from the straight line mode to the turning mode for control, and moves along the arc; when the reference point continues to run to the connection point of the arc and the straight line trajectory, it switches from the turning mode to the straight line mode for control.

[0043] By adopting the above technical scheme, the beneficial effects of the present invention are as follows: the method of the present invention is mainly suitable for AGV vehicles whose front wheel axle and rear wheel axle can be independently steered and controlled, and whose chassis system cannot be steered in place, and performs tracking control on straight and circular paths. The method is a magnetic navigation control method that combines two control modes, straight line and turning. Its turning control method is a dynamic deflection angle calculation of a fixed radius turning mode plus a PID control method of a static deflection angle. The method of the present invention adds a fixed control amount corresponding to the turning radius, so that when tracking a circular path with a fixed radius, the tracking effect of the AGV when performing a fixed radius turn is similar to that when tracking a straight path, thereby avoiding the situation in which the larger the turning radius during magnetic navigation, the larger the tracking error, resulting in AGV tracking loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 and Figure 2 The present invention relates to a dual PID tracking control method for an AGV with independent steering of the front and rear axles, and a schematic diagram of three coordinate systems of the vehicle in different modes.

[0045] Figure 3 The present invention relates to a dual PID tracking control method for an AGV with independent steering of front and rear axles, and a schematic diagram of the connection points of the switching modes. DETAILED DESCRIPTION

[0046] In order to further explain the technical solution of the present invention, the present invention is described in detail below through specific embodiments.

[0047] A dual PID tracking control method for an AGV with independently steerable front and rear axles. The AGV's front axle and rear axle can be independently steered. The tracking control method includes tracking control for a straight path, referred to as a straight-line mode, and tracking control for a turning path, referred to as a turning mode. Since the present invention is directed to AGVs with independently steerable front and rear axles, the front and rear wheels of the vehicle can be independently steered. The steps of the rear wheel tracking control method, whether in straight-line mode or turning mode, are identical to those of the front wheel. The following describes the tracking control method steps using the front wheel as an example.

[0048] In the linear mode, it is a common PID control mode, and the tracking control method steps are as follows:

[0049] 1) Obtain magnetic navigation positioning.

[0050] During tracking control, we focus on three coordinate systems: the vehicle front wheel coordinate system, the vehicle rear wheel coordinate system, and the vehicle center coordinate system. Figure 1 As shown, through the relationship between these coordinate systems, the positioning of the vehicle center relative to the magnetic navigation coordinate system is obtained, and the positioning of the vehicle center in the magnetic navigation coordinate system is obtained.

[0051] 2) The given linear speed is a fixed value.

[0052] The linear speed of the front and rear wheels of the vehicle is consistent, and a linear speed value is given.

[0053] 3) Calculate the lateral offset error, cumulative lateral offset error, and heading error from the center of the front axle of the front wheel to the arc path.

[0054] Through steps 1) and 2), first, calculate the lateral offset error of the front wheel from the center of the front axle to the arc path and record it as ,like Figure 1 As shown, that is, the shortest distance between the front wheel and the path, and when the front wheel is outside the path, the lateral error is set to be positive, and when it is inside the path, the lateral error is set to be negative;

[0055] Next, calculate the cumulative lateral offset error and record it as , the cumulative lateral offset error is the cumulative sum of the lateral offset errors calculated from the starting time to the current time;

[0056] Then, the heading error is calculated as ,like Figure 1 As shown, counterclockwise is positive, and the heading error is the front wheel heading. and the reference heading is recorded as The difference, that is , where the reference heading is the corresponding tangent direction of the front wheel at the nearest point on the arc, such as Figure 1 Direction of arrow shown.

[0057] 4) Determine the PID coefficient and calculate the dynamic front wheel deflection angle value corresponding to the PID.

[0058] In step 3) calculate the lateral error , cumulative lateral error and heading error After that, the PID parameters are determined through debugging and the corresponding dynamic front wheel deflection angle is obtained. .

[0059] 5) Determine the final front wheel deflection angle value.

[0060] The final front wheel deflection angle used for control is recorded as , the dynamic front wheel deflection angle obtained by step 4) As the final front wheel deflection angle value used for control, that is The calculation method for the rear wheel deflection angle is the same as that for the front wheel deflection angle.

[0061] 6) The final calculated front wheel deflection angle w is output to the controller as the actual control value, controlling the front wheel to deflect according to the set value.

[0062] 7) Return to step 2) and repeat the calculation cycle to achieve PID tracking control of the vehicle's front wheels.

[0063] The method steps for PID tracking control of the rear wheels of the vehicle are consistent with the method steps for PID tracking control of the front wheels. Those skilled in the art can directly substitute the above content to deduce it. They will not be repeated in this embodiment, and will not affect the clear understanding of the technical solution of the present invention by those skilled in the art.

[0064] In the turning mode with a fixed turning radius, a PID control method with a static value plus dynamic adjustment is used. The tracking control method steps are as follows:

[0065] S1) Obtain magnetic navigation positioning.

[0066] During tracking control, we focus on three coordinate systems: the vehicle front wheel coordinate system, the vehicle rear wheel coordinate system, and the vehicle center coordinate system. Figure 2 As shown, through the relationship between these coordinate systems, the positioning of the vehicle center relative to the magnetic navigation coordinate system is obtained, and the positioning of the vehicle center in the magnetic navigation coordinate system is obtained.

[0067] S2) The given linear speed is a fixed value.

[0068] The linear speed of the front and rear wheels of the vehicle is consistent, and a linear speed value is given.

[0069] S3) Calculate the lateral offset error, cumulative lateral offset error, and heading error from the front axle center of the front wheel to the arc path.

[0070] Through step S1) and step S2), first, calculate the lateral offset error of the front wheel from the center of the front axle to the arc path and record it as ,like Figure 2 As shown, that is, the shortest distance between the front wheel and the path, and when the front wheel is outside the path, the lateral error is set to be positive, and when it is inside the path, the lateral error is set to be negative;

[0071] Next, calculate the cumulative lateral offset error and record it as , the cumulative lateral offset error is the cumulative sum of the lateral offset errors calculated from the starting time to the current time;

[0072] Then, the heading error is calculated as ,like Figure 2 As shown, counterclockwise is positive, and the heading error is the front wheel heading. and the reference heading is recorded as The difference, that is , where the reference heading is the corresponding tangent direction of the front wheel at the nearest point on the arc, such as Figure 2 Direction of arrow shown.

[0073] S4) Determine the PID coefficient and calculate the dynamic front wheel deflection angle value corresponding to the PID.

[0074] In step S3) the lateral error is calculated , cumulative lateral error and heading error After that, the PID parameters are determined through debugging, and the corresponding dynamic front wheel deflection angle is recorded as .

[0075] .

[0076] S5) is recorded according to the wheelbase The turning radius is recorded as R, and the static deflection angle value corresponding to the front tire is recorded as .

[0077]

[0078] S6) Calculate the final front wheel deflection angle value.

[0079] According to the dynamic front wheel deflection angle and the static front wheel deflection angle, the final front wheel deflection angle used for control is calculated as The calculation method for the rear wheel deflection angle is the same as that for the front wheel deflection angle.

[0080] S7) The calculated final front wheel deflection angle w is output to the controller as the actual control value, and the front wheel is controlled to deflect according to the set value.

[0081] S8) Return to step S2) and perform calculations in a loop, thereby achieving PID tracking control of the vehicle's front wheels.

[0082] The method steps for PID tracking control of the rear wheels of the vehicle are consistent with the method steps for PID tracking control of the front wheels. Those skilled in the art can directly substitute the above content to deduce it. They will not be repeated in this embodiment, and will not affect the clear understanding of the technical solution of the present invention by those skilled in the art.

[0083] When AGV vehicles are in use, different modes are used for control in different sections of the road. The principle is to use the straight line mode control in the straight section and the turning mode control in the arc section, and stop and switch at the connection point. The purpose of stopping and switching is to prevent the vehicle from deviating too much from the track. Figure 3 As shown, when starting from the left straight line, the vehicle is in straight line mode control. When it moves to connection point 1, it switches from straight line mode to turning mode control. When the vehicle continues to move to connection point 2, it switches from turning mode to straight line mode control. Specific description: Taking the center of the line connecting the front and rear wheel axles of the vehicle as the reference point, the driving trajectory of the reference point is connected by a straight line and an arc. Taking starting from a straight section as an example, the mode switching rules are as follows: starting from a straight section, control is performed in straight line mode; when the reference point moves to the connection point of the straight line trajectory and the circular arc trajectory (i.e., as shown in the figure, connection point 1, about to enter the circular arc section), control is switched from straight line mode to turning mode and moves along the arc; when the reference point continues to move to the connection point of the circular arc and the straight line trajectory (i.e., as shown in the figure, connection point 2, about to enter the straight line section), control is switched from turning mode to straight line mode and returns to step 2 of straight line mode).

[0084] In addition, if the AGV vehicle in this embodiment is provided with a magnetic sensor at the center of the front axle of the front wheel and the center of the rear axle of the rear wheel, respectively, the two magnetic sensors respectively sense the magnetic nails on the path; step 1) and step S1) both obtain the magnetic navigation positioning of the two magnetic sensors; step 3) and step S3) are both performed in the following manner: when the two magnetic sensors sense the magnetic nails at the same time, the true value of the lateral error obtained by direct sensing by the magnetic sensors is used as a correction value instead of the lateral offset error for calculation; when the two magnetic sensors do not sense the magnetic nails at the same time, data from any sensor such as an odometer or an inertial measurement unit that can perform relative motion inference is obtained, and the lateral offset error is calculated based on the latest correction value, that is, the data of the two magnetic sensors is used as the correction value, and the data of other sensors such as the odometer or inertial measurement unit is used as the predicted value to calculate the lateral error of the front wheel or rear wheel relative to the reference path.

[0085] The above embodiments and drawings do not limit the product form and style of the present invention. Any appropriate changes or modifications made by ordinary technicians in the relevant technical field should be deemed to be within the patent scope of the present invention.

Claims

1. A dual PID tracking control method suitable for AGV with independent steering of front and rear axles, characterized in that: The front axle of the front wheel and the rear axle of the rear wheel of the AGV vehicle can be independently steered. The tracking control method includes tracking control of the turning path, which is recorded as a turning mode. The tracking control execution includes tracking control of the front wheel and the rear wheel. Since the front wheel and the rear wheel can be independently steered, the tracking control method is described by taking the tracking control execution of the front wheel as an example. The execution method steps of the rear wheel can be obtained by referring to the front wheel. The tracking control method steps of the front wheel are as follows: S1) Obtain magnetic navigation positioning; S2) The given linear speed is a fixed value; S3) calculating the lateral offset error, cumulative lateral offset error, and heading error from the center of the front axle of the front wheel to the arc path; S4) determining the PID coefficient and calculating the dynamic front wheel deflection angle value corresponding to the PID; S5) determining a static deflection angle value corresponding to the front tire; S6) determining a final front wheel deflection angle value; S7) outputting the calculated final front wheel deflection angle w as the actual control value to the controller to control the front wheel to deflect according to the set value; S8) Return to step 2) and perform calculation in a loop; Step S3) is as follows: Through step S1) and step S2), first, calculate the lateral offset error of the front wheel from the center of the front axle to the arc path and record it as , and the lateral error is set to positive when the front wheel is outside the path, and negative when the front wheel is inside the path; Next, calculate the cumulative lateral offset error and record it as , the cumulative lateral offset error is the cumulative sum of the lateral offset errors calculated from the starting time to the current time; Then, the heading error is calculated as , with counterclockwise as positive, the heading error is the front wheel heading and is recorded as and the reference heading is recorded as The difference, that is , where the reference heading is the corresponding tangent direction of the front wheel at the nearest point on the arc; Step S4) is to calculate the lateral error in step S3) , cumulative lateral error and heading error After that, the PID parameters are determined through debugging, and the corresponding dynamic front wheel deflection angle is recorded as , ； Step S5) is based on the wheelbase The turning radius is recorded as R, and the static deflection angle value corresponding to the front tire is recorded as , ； Step 6) is to calculate the final front wheel deflection angle used for control based on the dynamic front wheel deflection angle and the static front wheel deflection angle: ; The AGV vehicle is provided with a magnetic sensor at the center of the front axle of the front wheel and the center of the rear axle of the rear wheel, respectively. The two magnetic sensors respectively sense the magnetic nails on the path; in step 1), the magnetic navigation positioning of the two magnetic sensors is obtained; in step 3), when the two magnetic sensors sense the magnetic nails at the same time, the true value of the lateral error obtained by direct sensing by the magnetic sensors is used as the correction value instead of the lateral offset error for calculation; when the two magnetic sensors do not sense the magnetic nails at the same time, the sensor data of the odometer or inertial measurement unit is obtained to calculate the lateral offset error based on the latest correction value.

2. A dual PID tracking control method suitable for AGV with independent steering of front and rear axles, characterized in that: The front axle of the front wheel and the rear axle of the rear wheel of the AGV vehicle can be independently steered and controlled. The tracking control method includes tracking control of a straight path, which is recorded as a straight mode, and tracking control of a turning path, which is recorded as a turning mode. The tracking control execution of the straight mode and the turning mode includes tracking control of the front wheel and the rear wheel. Since the front wheel and the rear wheel can be independently steered and controlled, the tracking control method is described by taking the tracking control execution of the front wheel as an example. The execution method steps of the rear wheel can be obtained by referring to the front wheel. The steps of the front wheel tracking control method in the straight mode and / or the turning mode are as follows: Straight line mode: 1) Obtain magnetic navigation positioning; 2) The given linear speed is a fixed value; 3) Calculate the lateral offset error, cumulative lateral offset error, and heading error from the center of the front axle of the front wheel to the straight path; 4) Determine the PID coefficient and calculate the dynamic front wheel deflection angle value corresponding to the PID; 5) Determine the final front wheel deflection angle value; 6) The calculated final front wheel deflection angle w is output to the controller as the actual control value, controlling the front wheel to deflect according to the set value; 7) Return to step 2) and perform calculations in a loop to achieve PID tracking control of the vehicle's front wheels; Turning Mode: S1) Obtain magnetic navigation positioning; S2) The given linear speed is a fixed value; S3) calculating the lateral offset error, cumulative lateral offset error, and heading error from the center of the front axle of the front wheel to the arc path; S4) determining the PID coefficient and calculating the dynamic front wheel deflection angle value corresponding to the PID; S5) determining a static deflection angle value corresponding to the front tire; S6) determining a final front wheel deflection angle value; S7) outputting the calculated final front wheel deflection angle w as the actual control value to the controller to control the front wheel to deflect according to the set value; S8) Return to step 2) and perform calculation in a loop; In the straight line mode: Step 3) is this: Through steps 1) and 2), first, calculate the lateral offset error of the front wheel from the center of the front axle to the arc path and record it as , and the lateral error is set to positive when the front wheel is outside the path, and negative when the front wheel is inside the path; Next, calculate the cumulative lateral offset error and record it as , the cumulative lateral offset error is the cumulative sum of the lateral offset errors calculated from the starting time to the current time; Then, the heading error is calculated as , with counterclockwise as positive, the heading error is the front wheel heading and is recorded as and the reference heading is recorded as The difference, that is , where the reference heading is the corresponding tangent direction of the front wheel at the nearest point on the arc; Step 4) is to calculate the lateral error in step 3) , cumulative lateral error and heading error After that, the PID parameters are determined through debugging and the corresponding dynamic front wheel deflection angle is obtained. , Step 5) is as follows, the final front wheel deflection angle used for control is recorded as , the dynamic front wheel deflection angle obtained by step 4) As the final front wheel deflection angle value used for control, that is ; And / or, in the turning mode: Step S3) is as follows: Through step S1) and step S2), first, calculate the lateral offset error of the front wheel from the center of the front axle to the arc path and record it as , and the lateral error is set to positive when the front wheel is outside the path, and negative when the front wheel is inside the path; Next, calculate the cumulative lateral offset error and record it as , the cumulative lateral offset error is the cumulative sum of the lateral offset errors calculated from the starting time to the current time; Then, the heading error is calculated as , with counterclockwise as positive, the heading error is the front wheel heading and is recorded as and the reference heading is recorded as The difference, that is , where the reference heading is the corresponding tangent direction of the front wheel at the nearest point on the arc; Step S4) is to calculate the lateral error in step S3) , cumulative lateral error and heading error After that, the PID parameters are determined through debugging, and the corresponding dynamic front wheel deflection angle is recorded as , ； Step S5) is based on the wheelbase The turning radius is recorded as R, and the static deflection angle value corresponding to the front tire is recorded as , ； Step 6) is to calculate the final front wheel deflection angle used for control based on the dynamic front wheel deflection angle and the static front wheel deflection angle: ; The AGV vehicle is provided with a magnetic sensor at the center of the front axle of the front wheel and the center of the rear axle of the rear wheel, respectively, and the two magnetic sensors respectively sense the magnetic nails on the path; in both step 1) and step S1), the magnetic navigation positioning of the two magnetic sensors is obtained; in both step 3) and step S3), when the two magnetic sensors simultaneously sense the magnetic nails, the true value of the lateral error obtained by direct sensing by the magnetic sensors is used as the correction value instead of the lateral offset error for calculation; when the two magnetic sensors do not simultaneously sense the magnetic nails, the sensor data of the odometer or inertial measurement unit is obtained to calculate the lateral offset error based on the latest correction value.

3. A dual PID tracking control method for an AGV with independent steering of front and rear axles as claimed in claim 2, characterized in that: AGV vehicles use different modes for control in different sections. The straight line mode is used for straight sections, and the turning mode is used for arc sections. The mode is automatically switched at the connection point between the straight and arc sections. The rule for switching modes is as follows: the center of the line connecting the front and rear wheel axles of the vehicle is used as the reference point, and the driving trajectory of the reference point is connected by a straight line and an arc. Taking the straight line section as an example, the AGV vehicle is controlled in the straight line mode when it starts from the straight line section. When the reference point moves to the connection point of the straight track and the circular arc track, the control is switched from the straight line mode to the turning mode and moves along the arc; when the reference point continues to move to the connection point of the circular arc and the straight line track, the control is switched from the turning mode to the straight line mode.

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