A double-rudder AGV parameter automatic calibration method

Abstract

The application discloses a double-rudder AGV parameter automatic calibration method, which comprises the following steps: firstly, zero position offset calibration procedures are performed on a first rudder and a second rudder of a target double-rudder AGV to obtain a zero position offset value of the first rudder and a zero position offset value of the second rudder; then, the zero position offset values of the first rudder and the second rudder are written into an AGV controller to compensate for a zero position of a rudder steering instruction or a rudder feedback angle; and finally, after the zero position compensation takes effect, a vehicle-mounted pose perception sensor installation angle calibration procedure is performed to obtain an installation angle of the sensor in a vehicle body coordinate system. The application can automatically and efficiently complete key physical parameter calibration of the double-rudder AGV without relying on external sensors and manual operation, improves positioning and control precision of the AGV, and is suitable for batch production and rapid deployment of the double-rudder AGV.

Description

Technical Field

[0001] This application relates to the field of AGV (Automated Guided Vehicle) technology, and in particular to a method for automatic parameter calibration of a dual-steering wheel AGV. Background Technology

[0002] The dual-steering wheel chassis structure AGV is a widely used omnidirectional AGV with advantages such as high load capacity, small required channel width, and flexible route deployment. AGVs based on this chassis structure are widely used in scenarios such as lurking lifting docking, outdoor inter-building transfer, and narrow aisle vertical warehouses.

[0003] To improve the single-vehicle positioning accuracy and consistent performance across multiple dual-steering-wheel AGVs, physical parameter calibration is typically required before delivery or during maintenance. For dual-steering-wheel AGVs that use onboard sensing sensors (such as LiDAR and vision sensors) for navigation and positioning, key physical parameters include the zero-position offset of the two steering wheels and the installation angle of the onboard sensing sensors relative to the vehicle's coordinate system. The accuracy of these two parameters directly affects the motion control and positioning accuracy of the dual-steering-wheel AGV.

[0004] Among the currently disclosed parameter calibration methods, there are many for forklift AGVs, but relatively few for dual-steering-wheel AGVs. Some of the disclosed dual-steering-wheel parameter calibration methods require additional measurement sensors (such as laser trackers and total stations) and manual remote control operation, such as CN117406791A; others use laser point cloud registration technology for calibration, such as CN115435816A. However, this method requires the AGV controller to integrate complex point cloud processing algorithms, making it less suitable for AGVs that directly output pose sensors or AGVs with limited controller computing power.

[0005] In addition, existing calibration methods generally suffer from problems such as complex operation, reliance on professional personnel, and long time consumption, making it difficult to meet the needs of AGV mass production and rapid deployment.

[0006] Therefore, given the characteristics of dual-steering wheel AGVs, there is an urgent need for a simple, fast, versatile, and automated parameter calibration method to solve the problems existing in the current technology. Summary of the Invention

[0007] This application aims to solve the problems of complex operation, reliance on external equipment and manual intervention in the parameter calibration method of dual-steering wheel AGV in the prior art. It provides an automatic parameter calibration method for dual-steering wheel AGV that does not require additional sensors and is fully automated. It can efficiently and accurately complete the calibration of steering wheel zero position offset and vehicle posture perception sensor installation angle.

[0008] To solve the above-mentioned technical problems, this application provides the following technical solution:

[0009] An automatic parameter calibration method for a dual-steering wheel AGV, the method comprising the following steps:

[0010] S1, perform a zero-position offset calibration process on the first and second steering wheels of the target dual-steering wheel AGV to obtain the zero-position offset value of the first steering wheel and the zero-position offset value of the second steering wheel;

[0011] S2, write the zero offset value of the first steering wheel and the zero offset value of the second steering wheel into the AGV controller to perform zero-position compensation for the steering wheel steering command or steering wheel feedback angle.

[0012] S3. After the zero-position compensation takes effect, the vehicle posture perception sensor installation angle calibration process is executed to obtain the installation angle of the vehicle posture perception sensor in the vehicle coordinate system.

[0013] Preferably, the zero-position compensation for the steering wheel command or steering wheel feedback angle in S2 includes:

[0014] When sending a steering command to the steering wheel, the target steering angle is corrected based on the zero-position offset values ​​of the first and second steering wheels; or,

[0015] When reading the steering wheel feedback angle, the feedback angle is corrected based on the zero-position offset values ​​of the first and second steering wheels.

[0016] Preferably, the zero-position offset calibration process in S1 includes one or more calibration rounds, wherein each calibration round includes two unidirectional movements in opposite directions, denoted as the first unidirectional movement and the second unidirectional movement, respectively.

[0017] The first unidirectional motion performs the following steps:

[0018] S11, when the AGV is stationary, set the initial setting angle of the first steering wheel and the initial setting angle of the second steering wheel, read the real-time angle feedback value output by the steering drive corresponding to the first steering wheel and the second steering wheel as the feedback measurement angle, and collect the starting heading angle.

[0019] S12, control the AGV to travel a set distance in the first direction, stop when either steering wheel reaches the set distance, record the actual travel distance of the first and second steering wheels, and collect the ending heading angle;

[0020] S13, based on the starting heading angle, ending heading angle, actual travel distance of the first and second steering wheels, and feedback measurement angles of the first and second steering wheels, calculate the zero-position offset value of the first and second steering wheels corresponding to this unidirectional movement.

[0021] The second unidirectional motion performs the following steps:

[0022] S14, when the AGV is stationary at the end position of the first unidirectional motion, keep the first steering wheel and the second steering wheel at the same initial set angle as the first unidirectional motion, read the real-time angle feedback value output by the steering drive corresponding to the first steering wheel and the second steering wheel as the feedback measurement angle, and collect the starting heading angle;

[0023] S15, control the AGV to travel a set distance in the opposite direction to the first direction, stop when either steering wheel reaches the set distance, record the actual travel distance of the first steering wheel and the second steering wheel, and collect the ending heading angle;

[0024] S16. Based on the initial heading angle, the final heading angle, the actual travel distance of the first and second steering wheels, and the feedback measurement angles of the first and second steering wheels, calculate the zero-position offset value of the first and second steering wheels corresponding to this unidirectional movement.

[0025] Preferably, the zero-position offset calibration process in S1 further includes:

[0026] S17, take the average of the zero offset values ​​of the two first steering wheels and the two second steering wheels obtained from two unidirectional movements in opposite directions during the calibration of the same wheel, and use them as the zero offset values ​​of the first steering wheel and the second steering wheel for calibration in this round.

[0027] S18, repeat the calibration multiple times until the preset first termination condition is met, and take the average of the zero-position offset values ​​of the first steering wheel and the second steering wheel obtained from all calibration rounds as the final zero-position offset values ​​of the first steering wheel and the second steering wheel.

[0028] The first termination condition includes: reaching the preset maximum number of calibration wheels, or the difference between the zero offset value of the first steering wheel obtained by the current calibration and the zero offset value of the first steering wheel obtained by the previous calibration, and the difference between the zero offset value of the second steering wheel obtained by the current calibration and the zero offset value of the second steering wheel obtained by the previous calibration are all less than the preset first convergence threshold.

[0029] Preferably, the initial setting angle of the first steering wheel and the initial setting angle of the second steering wheel are a pair of non-zero angles of equal magnitude and opposite sign, so that the AGV generates a heading angle change during driving that can be distinguished by the on-board posture sensing sensor.

[0030] The absolute value of the initial set angle is greater than 0° and does not exceed a first preset threshold, which is determined based on at least one of the AGV's wheelbase, maximum allowable turning radius, or calibrated site dimensions.

[0031] Preferably, the starting heading angle and the ending heading angle are both obtained by arithmetically averaging the heading angle components in N consecutive pose data acquisitions from the vehicle-mounted pose perception sensor, where N is an integer greater than 1.

[0032] Preferably, the step of calculating the zero-position offset value of the first steering wheel and the second steering wheel corresponding to this unidirectional movement based on the initial heading angle, the final heading angle, the actual travel distance of the first steering wheel and the second steering wheel, and the feedback measurement angle of the first steering wheel and the second steering wheel includes:

[0033] S131, Calculate the angle turned by the AGV body in this unidirectional movement based on the difference between the starting heading angle and the ending heading angle;

[0034] S132, Based on the angle turned by the AGV body in this unidirectional movement and the actual travel distance of the first steering wheel and the second steering wheel, calculate the rotation radius of the first steering wheel and the second steering wheel respectively;

[0035] S133, based on the rotation radius of the first and second steering wheels and the coordinates of the mounting points of the first and second steering wheels in the vehicle coordinate system, solve for the intersection of two circles with the two mounting points as centers and the corresponding rotation radii as radii, and select the unique and effective instantaneous rotation center.

[0036] S134, Calculate the actual physical rotation angle of the first and second steering wheels based on the coordinates of the instantaneous rotation center;

[0037] S135, the actual physical rotation angles of the first and second steering wheels are subtracted from the corresponding feedback measurement angles to obtain the zero-position offset values ​​of the first and second steering wheels corresponding to this unidirectional movement.

[0038] Preferably, calculating the actual physical rotation angle of the first and second steering wheels based on the coordinates of the instantaneous rotation center in step S134 includes:

[0039] Based on the coordinates of the instantaneous rotation center in the vehicle coordinate system, calculate the first vector pointing to the first steering wheel mounting point and the second vector pointing to the second steering wheel mounting point.

[0040] When the instantaneous rotation center is located to the left of the vector pointing from the second steering wheel mounting point to the first steering wheel mounting point, the first vector / second vector is rotated counterclockwise by 90° to obtain the direction vector of the corresponding steering wheel;

[0041] When the instantaneous rotation center is located to the right of the vector pointing from the second steering wheel mounting point to the first steering wheel mounting point, rotate the first vector / second vector clockwise by 90°, or add π to the direction vector after rotating it counterclockwise by 90° to obtain the direction vector of the corresponding steering wheel;

[0042] Based on the direction vector, the actual physical rotation angle is calculated using the arctangent function and normalized to the interval (-π, π] to obtain the actual physical rotation angle of the first and second steering wheels.

[0043] Preferably, the vehicle-mounted pose perception sensor installation angle calibration process in S3 includes one or more calibrations, and each calibration includes the following steps:

[0044] S31, after the zero-position compensation takes effect, a zero-reset command is sent to the steering drive of the first steering wheel and the second steering wheel so that the feedback measurement angles of the first steering wheel and the second steering wheel converge to a preset tolerance range centered on 0°.

[0045] S32, control the AGV to travel forward a preset short distance and then stop, and continuously collect the pose data of the vehicle pose perception sensor during the travel process. The preset short distance satisfies the condition that the actual travel trajectory of the AGV can be approximated as a straight line when the feedback measurement angle of the first steering wheel and the second steering wheel is within the preset tolerance range.

[0046] S33, Based on the position components in the collected pose data, perform linear fitting to obtain a fitted straight line, and calculate the actual driving direction angle of the AGV body according to the slope of the fitted straight line.

[0047] S34, calculate the arithmetic mean of the attitude angle components in the collected pose data to obtain the average azimuth angle of the vehicle pose sensing sensor;

[0048] S35, based on the difference between the average azimuth angle and the actual driving direction angle, determine the installation angle of the vehicle posture perception sensor in the vehicle coordinate system for this calibration.

[0049] Preferably, the vehicle-mounted pose perception sensor installation angle calibration process in S3 further includes:

[0050] The calibration process is repeated multiple times until a preset second termination condition is met. The average of all calibration results is then taken as the final installation angle of the vehicle-mounted pose sensing sensor.

[0051] The second termination condition includes: reaching the preset maximum number of calibrations, or the absolute difference between the installation angle of the vehicle pose perception sensor in the vehicle coordinate system obtained in the current calibration and the installation angle of the vehicle pose perception sensor in the vehicle coordinate system obtained in the previous calibration is less than the preset second convergence threshold.

[0052] Compared with the prior art, this application has the following beneficial effects:

[0053] 1. The entire calibration process requires no manual intervention or additional measuring equipment and is completed autonomously by the AGV, which greatly improves calibration efficiency and is suitable for mass production and rapid on-site deployment of dual-steering wheel AGVs;

[0054] 2. By employing reciprocating motion, multiple iterations, and result averaging, single-measurement noise and systematic bias are effectively eliminated, ensuring high accuracy and stability of the calibration results;

[0055] 3. The method does not depend on a specific type of pose perception sensor (such as LiDAR, visual SLAM, etc.), as long as it can output a stable pose, it has a wide range of applications;

[0056] 4. The calibration process is reasonably designed, making full use of the AGV's own kinematic characteristics and sensor data, with clear control logic and high reliability. Attached Figure Description

[0057] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0058] Figure 1 This is a flowchart illustrating an automatic parameter calibration method for a dual-steering wheel AGV according to an embodiment of this application.

[0059] Figure 2 This is a schematic diagram of the geometric relationship between the AGV's motion and instantaneous rotation center during the calibration of the steering wheel zero-position offset in the embodiments of this application;

[0060] Figure 3 This is a schematic diagram illustrating the geometric relationship for determining the instantaneous rotation center coordinates by solving the intersection point of two circles in an embodiment of this application.

[0061] Figure 4 This is a schematic diagram illustrating the determination of the actual motion direction angle of the AGV based on linear fitting of the LiDAR positioning point in an embodiment of this application.

[0062] Figure 5This is a schematic diagram of the coordinate system and angle relationship during the lidar installation angle calibration process in the embodiments of this application. Detailed Implementation

[0063] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0064] In the embodiments provided in this application, it should be understood that the disclosed methods and systems can be implemented in other ways. The system embodiments described below are merely illustrative. For example, the division of units and modules is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or modules can be combined, or integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the various components shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or modules, and can be electrical, mechanical, or other forms.

[0065] In addition, each functional unit in the various embodiments of this application can be integrated into a single processor, or each unit can be a separate device, or two or more units can be integrated into a single device; each functional unit in the various embodiments of this application can be implemented in hardware or in the form of hardware plus software functional units.

[0066] Those skilled in the art will understand that all or part of the steps of the following method embodiments can be implemented by program instructions and related hardware. The aforementioned program instructions can be stored in a computer-readable storage medium. When the program instructions are executed, they perform the steps of the following method embodiments. The aforementioned storage medium includes various media capable of storing program code, such as mobile storage devices, read-only memory (ROM), magnetic disks, or optical disks.

[0067] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "a plurality of" or "several" means two or more, unless otherwise explicitly specified.

[0068] like Figure 1 As shown in the figure, this application provides an automatic parameter calibration method for a dual-steering wheel AGV, which may include the following steps:

[0069] S1, perform a zero-position offset calibration process on the first and second steering wheels of the target dual-steering wheel AGV to obtain the zero-position offset value of the first steering wheel and the zero-position offset value of the second steering wheel.

[0070] In the physical world of AGVs, the zero position is usually defined as the state where the rolling direction of the steering wheel is completely parallel to the longitudinal axis of the AGV body. However, due to wear during manufacturing, assembly, or long-term use, there is often a fixed systematic deviation between the physical zero position of the steering wheel and the 0-degree reading reported by the angle sensor (such as an encoder) inside the steering drive. This deviation is the zero position offset value.

[0071] The goal of this step is to quantify and obtain the zero-offset values ​​of the two independent steering wheels (i.e., the first and second steering wheels) on the dual-steering-wheel AGV. This deviation is identified through an automated calibration process that utilizes the AGV's own motion capabilities and its onboard posture perception sensors (such as LiDAR, visual SLAM modules, etc.). Under the control of the controller, the AGV executes a series of preset autonomous movements. During this process, the system simultaneously collects global posture information from the posture perception sensors (used to determine the overall motion state of the AGV) and angle feedback data from the steering wheel drive. By analyzing the inconsistency between the AGV's actual motion trajectory and the steering wheel feedback angle, this process can reverse-engineer the actual physical orientation of each steering wheel to produce the observed motion. Comparing this calculated actual physical orientation with the measured angle fed back by the steering wheel, the difference is determined as the zero-offset value of that steering wheel. Finally, this step outputs two specific values: the zero-offset value of the first steering wheel and the zero-offset value of the second steering wheel.

[0072] For example, suppose a dual-steering-wheel AGV to be calibrated starts this process. After running autonomously for a period of time, the system's internal algorithm completes the calculations and concludes that when the driver of the first steering wheel (e.g., the front wheel) reports its angle as 0 degrees, its actual physical orientation deviates from the vehicle's longitudinal axis by +0.75 degrees; while when the driver of the second steering wheel (e.g., the rear wheel) reports 0 degrees, its actual physical orientation deviates from the longitudinal axis by -0.42 degrees. Therefore, step S1 successfully obtained the zero-position offset value of the first steering wheel as +0.75 degrees and the zero-position offset value of the second steering wheel as -0.42 degrees.

[0073] S2, write the zero offset value of the first steering wheel and the zero offset value of the second steering wheel into the AGV controller to perform zero-position compensation for steering wheel steering commands or steering wheel feedback angles;

[0074] After successfully obtaining the precise zero-position offset values ​​of the two steering wheels in step S1, the next step is to apply these calibration parameters to the AGV's control system so that it can automatically correct the control errors caused by the zero-position offset during subsequent operation. The main operator for this step is the AGV's main controller (or related control software module).

[0075] Specifically, step S2 writes the two zero-position offset values ​​output from S1 as key configuration parameters into the AGV controller's storage unit. Once written, the controller activates a zero-position compensation mechanism. This mechanism dynamically compensates for the known zero-position offset in the AGV's steering control loop. Whether the controller adjusts the commands sent to the steering wheel or corrects the feedback read from the steering wheel, its ultimate goal is to ensure that, at the control logic level, the steering wheel angle information accurately reflects its physical orientation, thereby enabling the AGV's motion control commands to be executed precisely. After this step, the control accuracy of the steering wheel system is fundamentally improved, laying a solid foundation for subsequent sensor calibration.

[0076] Continuing with the example of S1, the controller saves the values ​​of +0.75 degrees and -0.42 degrees to its internal parameter table and enables the compensation function. From then on, whenever the AGV needs to perform a steering operation, its control system will automatically use these two values ​​for correction. For example, when executing a straight-ahead command, the system can ensure that the physical orientation of both steering wheels is precisely aligned with the longitudinal axis of the vehicle body, preventing the vehicle from veering off course due to inherent zero-position offset.

[0077] S3, after the zero-position compensation takes effect, execute the vehicle posture perception sensor installation angle calibration process to obtain the installation angle of the vehicle posture perception sensor in the vehicle coordinate system.

[0078] After the zero-position error of the steering wheel is effectively compensated (i.e., step S2 takes effect), the AGV gains the ability to perform high-precision linear motion. At this point, the second key parameter can be addressed: the installation angle error of the onboard pose sensing sensor. This sensor (such as a lidar) is fixed to the AGV body via a mechanical bracket, ideally with its own coordinate system (especially its 0-degree azimuth angle) perfectly aligned with the AGV's coordinate system. However, in actual installation, a slight angular deviation is always introduced.

[0079] Step S3 aims to accurately measure this installation angle deviation. Its basic principle is to use a pre-calibrated steering wheel system to allow the AGV to perform a known, ideal linear motion. Then, by analyzing the sensor's perception of this motion, its installation deviation is deduced. In this process, the AGV executes a controlled linear movement under the controller's instructions. Simultaneously, the system continuously records the pose data stream output by the onboard pose sensing sensor. By performing specific mathematical processing and analysis on this data stream, the difference between the motion direction reported by the sensor and its actual physical motion direction can be separated. This difference is the sensor's installation angle in the vehicle coordinate system. The output of this step is a single angle value that fully describes the rotational relationship between the sensor coordinate system and the vehicle coordinate system.

[0080] After S2 takes effect, the AGV executes the S3 procedure. The AGV is commanded to move forward a short distance. During this time, the top-mounted LiDAR continuously outputs its positioning results. After the procedure ends, the system analyzes all data and finds that the LiDAR perceives the AGV's direction of travel as 1.8 degrees east of due north, while according to the calibrated steering wheel system, the AGV's actual direction of travel is due north (0 degrees). Therefore, the system determines that the LiDAR's installation angle is +1.8 degrees, meaning that its own coordinate system's 0-degree direction is 1.8 degrees east of the vehicle's 0-degree direction. This result will be used for subsequent navigation to ensure that the positioning information is precisely synchronized with the vehicle's movement.

[0081] In summary, this embodiment provides an overall framework for an automatic parameter calibration method for a dual-steering-wheel AGV. The method consists of three stages. First, in stage S1, the AGV autonomously executes a specific motion trajectory (such as arc driving) and uses its onboard posture perception sensors (such as lidar) to record the initial and final posture and position information. Combined with the actual travel distance feedback from the steering wheel encoders, the zero-position offset of the two steering wheels is deduced. Second, in stage S2, the calculated zero-position offset value is written to the AGV's main controller. The controller can apply this compensation value in two ways: one is to subtract the zero-position offset value from the target angle before issuing the steering command to ensure the steering wheel actually turns to the desired angle; the other is to add the zero-position offset value after reading the steering wheel feedback angle to obtain the true physical orientation angle. Finally, in stage S3, using the steering wheel system that has undergone zero-position compensation, the AGV is controlled to perform precise linear motion. The installation angle deviation of the sensors relative to the vehicle coordinate system is calculated again using data from the posture perception sensors.

[0082] For example, suppose a newly manufactured dual-steering-wheel AGV needs calibration. The operator simply clicks the "Start Calibration" button on the HMI, and the AGV automatically executes the entire process from S1 to S3. For instance, in S1, the zero-position offset of the front steering wheel is calculated to be +0.8°, and that of the rear steering wheel to be -0.5°. In S2, these two values ​​are immediately written to the controller. Then, in S3, the AGV uses the corrected steering wheel system to move forward 0.5 meters and finally calculates that its top-mounted lidar has an installation deviation of +1.2° relative to the direction of the vehicle's head. The entire process is completed in a short time (e.g., 5 minutes), while traditional methods might require a professional engineer to spend more than half an hour.

[0083] The core advantage of this embodiment lies in providing an end-to-end, fully automated calibration solution. This solution decomposes the complex physical parameter calibration problem into two independently executable sub-tasks (steering wheel zero-position calibration and sensor mounting angle calibration), and establishes the dependency between the two through step S2, ensuring the logical rigor and accuracy of the entire calibration process. The entire process requires no manual intervention or external high-precision measuring equipment, greatly improving the deployment efficiency of AGVs on production lines or in the field.

[0084] It should be noted that the first and second steering wheels on a dual-steering-wheel AGV can be arranged symmetrically, with the first steering wheel installed at the center or near the center of the front of the AGV body and the second steering wheel installed at the center or near the center of the rear of the AGV body; they can also be arranged symmetrically from side to side, with the two steering wheels arranged laterally on both sides of the vehicle body, i.e., the first steering wheel installed on the left side of the AGV body and the second steering wheel installed on the right side of the AGV body; or they can be arranged asymmetrically / offset, i.e., the first steering wheel is installed at the front of the vehicle body but offset to the left or right, and the second steering wheel is installed at the rear of the vehicle body, possibly also offset. In this embodiment, the first and second steering wheels in the dual-steering-wheel AGV are arranged symmetrically, i.e., the first steering wheel is the front steering wheel and the second steering wheel is the rear steering wheel, and the two are arranged along the longitudinal centerline of the vehicle body, together constituting the main drive, steering and load-bearing unit of the AGV.

[0085] In one embodiment, zero-position compensation for the steering wheel command or steering wheel feedback angle in S2 includes:

[0086] When sending a steering command to the steering wheel, the target steering angle is corrected based on the zero-position offset values ​​of the first and second steering wheels; or,

[0087] When reading the steering wheel feedback angle, the feedback angle is corrected based on the zero-position offset values ​​of the first and second steering wheels.

[0088] This embodiment details how to apply the zero-position offset value in an AGV control system, and provides two equivalent compensation strategies with different implementation positions.

[0089] 1. Command Correction Mode: When the upper-level motion planning module wants the steering wheel to turn to the target angle... Before sending commands to the underlying steering drive, the controller will first calculate the corrected command angle. Due to the presence of the steering wheel The zero offset when it executes When the command is given, its actual physical orientation angle is: This allows for precise achievement of the target.

[0090] 2. Feedback Correction Mode: The steering drive directly executes the original commands from the upper level. However, due to the zero-position offset, the angle of its feedback... At this time, the controller receives... Then, the actual physical orientation angle will be calculated immediately. and will Used for subsequent motion control closed loops (such as PID control, trajectory tracking, etc.).

[0091] The technical advantage of this embodiment lies in its flexibility and compatibility. Different AGV software architectures may be better suited to one of the modes. The instruction correction mode places the compensation logic at the front end, making the underlying driver believe it is executing the correct instruction; while the feedback correction mode maintains the originality of the instruction, placing the compensation in the state estimation stage. Regardless of the method used, the impact of zero-position offset on control accuracy can be effectively eliminated, and the two methods are mathematically equivalent.

[0092] For example, suppose the zero-position offset of the front steering wheel is +1.0°.

[0093] In command correction mode, if the motion plan requires the steering wheel to point to 0° (straight ahead), the controller will send a -1.0° command to the drive. Due to the +1.0° offset, the actual physical orientation of the steering wheel is -1.0° + 1.0° = 0°, achieving straight ahead without deviation.

[0094] In feedback correction mode, the controller directly sends a 0° command. The actual physical orientation of the steering wheel is 0° + 1.0° = +1.0°, but its encoder feeds back 0°. After receiving 0°, the controller adds the offset value to obtain the true orientation +1.0°, and uses this +1.0° in the control algorithm to determine whether the vehicle is veering off course, thereby issuing a correction command.

[0095] In one embodiment, the zero-position offset calibration process in S1 includes one or more calibration rounds, wherein each calibration round includes two unidirectional movements in opposite directions, denoted as the first unidirectional movement and the second unidirectional movement, respectively.

[0096] The first unidirectional motion executes the following steps:

[0097] S11, when the AGV is stationary, set the initial setting angle of the first steering wheel and the initial setting angle of the second steering wheel, read the real-time angle feedback value output by the steering drive corresponding to the first steering wheel and the second steering wheel as the feedback measurement angle, and collect the starting heading angle.

[0098] S12, control the AGV to travel a set distance in the first direction, stop when either steering wheel reaches the set distance, record the actual travel distance of the first and second steering wheels, and collect the ending heading angle;

[0099] S13. Based on the starting heading angle, ending heading angle, actual travel distance of the first and second steering wheels, and feedback measurement angles of the first and second steering wheels, calculate the zero-position offset value of the first and second steering wheels corresponding to this unidirectional movement.

[0100] The second unidirectional motion executes the following steps:

[0101] S14, when the AGV is stationary at the end position of the first unidirectional motion, keep the first steering wheel and the second steering wheel at the same initial set angle as the first unidirectional motion, read the real-time angle feedback value output by the steering drive corresponding to the first steering wheel and the second steering wheel as the feedback measurement angle, and collect the starting heading angle;

[0102] S15, control the AGV to travel a set distance in the opposite direction to the first direction, stop when either steering wheel reaches the set distance, record the actual travel distance of the first and second steering wheels, and collect the ending heading angle;

[0103] S16. Based on the initial heading angle, the final heading angle, the actual travel distance of the first and second steering wheels, and the feedback measurement angles of the first and second steering wheels, calculate the zero-position offset value of the first and second steering wheels corresponding to this unidirectional movement.

[0104] This embodiment provides a specific execution process for calibrating the zero-position offset value of the steering wheel of a dual-steering wheel AGV. Its core lies in designing a complete calibration cycle. One calibration cycle consists of two consecutive unidirectional movements (outward and return). Through one outward and one return movement, two sets of independent but highly correlated observation data are provided for the calculation of the zero-position offset, thus laying the foundation for obtaining more reliable calibration results.

[0105] In the first unidirectional movement, when the AGV is stationary, the steering wheel angle is set, and its feedback value and initial heading angle are recorded. Then, it travels along the first direction for a preset distance and stops, recording the feedback measurement angle of each steering wheel, the actual travel distance, and the initial / final heading angle. Finally, a set of zero-position offset values ​​is calculated based on these data. Immediately following, the second unidirectional movement begins. The AGV maintains the steering wheel setting angle unchanged and travels the same preset distance in the opposite direction from its current position. Similarly, the feedback measurement angle, actual travel distance, and initial / final heading angle are recorded throughout the process, and a second set of zero-position offset values ​​is calculated independently.

[0106] The one-round calibration process in this embodiment effectively eliminates systematic biases. When the AGV moves forward and backward, asymmetry in its mechanical structure (such as gear backlash and tire deformation) may introduce direction-related errors. By performing a reciprocating motion, these direction-related errors are canceled out in subsequent averaging steps, resulting in a zero-position offset estimate that is closer to the true value. Furthermore, the reciprocating motion design allows the AGV to complete calibration within a limited space, improving its site adaptability.

[0107] For example, in a calibration, the first forward motion calculates a zero-position offset of +0.9° for the front steering wheel, which may include friction errors unique to forward motion. The subsequent backward motion, due to different friction characteristics, might calculate an offset of +0.7°. Both values ​​include systematic errors in their respective directions, but their average of +0.8° better approximates the true zero-position offset.

[0108] In one embodiment, the zero-offset calibration process in S1 further includes:

[0109] S17, take the average of the zero offset values ​​of the two first steering wheels and the two second steering wheels obtained from two unidirectional movements in opposite directions during the calibration of the same wheel, and use them as the zero offset values ​​of the first steering wheel and the second steering wheel for calibration in this round.

[0110] S18, repeat the calibration multiple times until the preset first termination condition is met, and take the average of the zero-position offset values ​​of the first steering wheel and the second steering wheel obtained from all calibration rounds as the final zero-position offset values ​​of the first steering wheel and the second steering wheel.

[0111] The first termination condition includes: reaching the preset maximum number of calibration wheels, or the difference between the zero offset value of the first steering wheel obtained from the current calibration and the zero offset value of the first steering wheel obtained from the previous calibration, and the difference between the zero offset value of the second steering wheel obtained from the current calibration and the zero offset value of the second steering wheel obtained from the previous calibration are all less than the preset first convergence threshold.

[0112] This embodiment adds data processing and flow control logic to the previous embodiment. Step S17 calculates the arithmetic mean of the two sets of zero-position offset values ​​obtained from two round trips in the same cycle to obtain the final result of this round. Step S18 controls the entire calibration process to repeat multiple rounds (e.g., up to 5 rounds) until a preset first termination condition is met. There are two types of first termination conditions: one is reaching the maximum number of rounds, which ensures that the calibration process will terminate within a finite number of steps; the other is checking whether the difference between the calibration result of the current round and the previous round is small enough (e.g., less than 0.1°), indicating that the calibration result has converged and stabilized, and no further iteration is needed.

[0113] This embodiment effectively improves the robustness and accuracy of calibration results. Single measurements are easily affected by random noise (such as minor ground unevenness or momentary sensor jitter). By repeating measurements multiple times and averaging the results, random noise can be effectively suppressed. Simultaneously, a convergence judgment mechanism is introduced, allowing the calibration process to automatically stop when the results are sufficiently accurate, avoiding unnecessary repetition and balancing efficiency and accuracy.

[0114] For example, suppose the maximum number of rounds is preset to 5 and the first convergence threshold is 0.1°.

[0115] The first round of calibration yielded the following zero-position offset values: the first steering wheel zero-position offset was +0.85°, and the second steering wheel zero-position offset was -0.48°. The second round of calibration yielded the following zero-position offset values: the first steering wheel zero-position offset was +0.82°, and the second steering wheel zero-position offset was -0.46°.

[0116] Calculate the difference: the change in the first steering wheel offset is |+0.82°-(+0.85°)|=0.03°; the change in the second steering wheel offset is |-0.46°-(-0.48°)|=0.02°.

[0117] Since the deviation changes of both steering wheels were less than the first convergence threshold of 0.1°, the system determined that the calibration results had converged, and terminated the calibration process early, even though the maximum number of rounds (5) had not been reached. Finally, the results from the two rounds were averaged.

[0118] The final offset of the first steering wheel is (+0.85° + 0.82°) / 2 = +0.835°; the final offset of the second steering wheel is (-0.48° + (-0.46°)) / 2 = -0.47°.

[0119] This result integrates data from multiple rounds of observations, effectively suppressing random errors from a single measurement, and is more reliable than the results from any single round.

[0120] In one embodiment, the initial setting angle of the first steering wheel and the initial setting angle of the second steering wheel are a pair of non-zero angles of equal magnitude and opposite sign, so that the AGV generates a heading angle change during driving that can be distinguished by the on-board posture perception sensor.

[0121] The absolute value of the initial set angle is greater than 0° and does not exceed the first preset threshold. The first preset threshold is determined based on at least one of the AGV's wheelbase, maximum allowable turning radius, or calibrated site dimensions.

[0122] This embodiment specifies the conditions that the initial setting angles for the steering wheel in steps S11 and S14 must meet: they must be a pair of non-zero angles of equal magnitude and opposite sign (such as +α and -α). The purpose of this setting is to ensure that the AGV generates a significant change in heading angle (Δφ) that can be distinguished by the onboard posture sensing sensor during movement. If the angle is 0, the AGV will travel in a straight line, Δφ≈0, which will lead to division by zero errors or unstable values ​​when calculating the rotation radius later. Simultaneously, the absolute value of the angle cannot be too large; an upper limit must be determined based on the AGV's physical dimensions (wheelbase), turning capability (maximum permissible turning radius), or site limitations.

[0123] This embodiment ensures the feasibility and safety of the calibration algorithm. A suitable initial setting angle can generate a sufficiently large Δφ to ensure calculation accuracy, while preventing the AGV from slipping, overturning, or exceeding the calibration area due to an excessively small turning radius. This is a key design that strikes a balance between theoretical feasibility and engineering practice.

[0124] For example, for an AGV with a wheelbase of 1 meter, if the initial angle is set to ±30°, its theoretical turning radius is approximately 0.87 meters, which may lead to excessively sharp turns. Therefore, based on its maximum permissible turning radius of 2 meters, the maximum permissible angle can be deduced to be approximately ±14°. Thus, choosing ±5° as the initial angle setting is a safe and effective compromise, producing a heading angle change of approximately 5° to 10° while ensuring driving stability.

[0125] In one embodiment, both the starting heading angle and the ending heading angle are obtained by arithmetically averaging the heading angle components from N consecutive pose data acquisitions by the vehicle-mounted pose perception sensor, where N is an integer greater than 1.

[0126] This embodiment optimizes the operation of acquiring the starting and ending heading angles in S11, S12, S14, and S15. It continuously acquires pose data N times (N>1, such as N=10) and performs an arithmetic mean on the heading angle components. This average value is used as the final starting or ending heading angle.

[0127] This embodiment effectively suppresses random noise from the sensor. The heading angle output by any pose sensing sensor (such as laser SLAM) exhibits a certain degree of jitter or noise. A single reading may deviate significantly from the true value. By averaging multiple samples, this high-frequency noise can be significantly smoothed out, resulting in a more stable heading angle that is closer to the true value, thereby improving the accuracy of subsequent Δφ calculations.

[0128] For example, when acquiring the initial heading angle, 10 consecutive readings are [10.1°, 10.3°, 9.9°, 10.2°, 10.0°, 10.4°, 9.8°, 10.1°, 10.2°, 10.0°]. Their arithmetic mean is 10.1°, while the maximum deviation of a single reading can reach ±0.3°. Using the average value as the initial heading angle can effectively avoid calibration failures caused by a single abnormal reading.

[0129] In one embodiment, the calculation of the zero-position offset values ​​of the first and second steering wheels corresponding to this unidirectional movement, based on the initial heading angle, the final heading angle, the actual travel distance of the first and second steering wheels, and the feedback measurement angles of the first and second steering wheels, includes:

[0130] S131, Calculate the angle turned by the AGV body in this unidirectional movement based on the difference between the starting heading angle and the ending heading angle;

[0131] S132, Based on the angle turned by the AGV body in this unidirectional movement and the actual travel distance of the first and second steering wheels, calculate the rotation radius of the first and second steering wheels respectively;

[0132] S133, based on the rotation radius of the first and second steering wheels and the coordinates of the mounting points of the first and second steering wheels in the vehicle coordinate system, solve for the intersection of two circles with the two mounting points as centers and the corresponding rotation radii as radii, and select the unique and effective instantaneous rotation center.

[0133] S134, calculate the actual physical rotation angle of the first and second steering wheels based on the coordinates of the instantaneous rotation center;

[0134] S135, the actual physical rotation angles of the first and second steering wheels are subtracted from the corresponding feedback measurement angles to obtain the zero-position offset values ​​of the first and second steering wheels corresponding to this unidirectional motion.

[0135] This embodiment decomposes the calculation of the zero-position offset value in S13 and S16 into five ordered sub-steps (S131-S135). First (S131), the total angle Δφ rotated by the AGV body is calculated by the difference between the starting and ending heading angles. Next (S132), using Δφ and the actual travel distance d of each steering wheel, the rotation radius of each steering wheel is calculated according to the circular motion formula R=d / Δφ. Then (S133), based on the known coordinates of the steering wheel mounting point and the calculated rotation radius, the unique instantaneous rotation center is found by solving the geometric method of the intersection of two circles. After that (S134), based on the position of the instantaneous rotation center, the true physical orientation angle that the steering wheel should have in this movement is calculated. Finally (S135), the difference between this true angle and the measured angle fed back by the steering wheel is used to obtain the zero-position offset value of this unidirectional movement.

[0136] This embodiment provides a complete, rigorous, and automatically executable geometric analysis method that can accurately deduce the local zero-position offset error of each steering wheel from the macroscopic overall motion state of the AGV (heading angle change) and the microscopic wheel-end motion data (travel distance, feedback measurement angle). This method does not rely on external measuring equipment and can complete high-precision self-calibration using only the AGV's own sensors and actuators, significantly improving the autonomous maintenance capability and control accuracy of dual-steering-wheel AGVs.

[0137] For example, assuming that in one motion, Δφ = 0.1745 radians (10°), the distance traveled by the front steering wheel is d. f =1.047 meters. Therefore, its radius of rotation R f =1.047 / 0.1745≈6 meters. If the coordinates of the front rudder wheel mounting point A are (0.5, 0) and the rear rudder wheel B is (-0.5, 0), then the radius R of the rear rudder wheel... r =5 meters, then the instantaneous rotation center point C can be found by solving the equation. Then, the true orientation of the front steering wheel can be calculated from point C as 5.71°, while its feedback angle is 5.0°, so the zero position offset is +0.71°.

[0138] In one embodiment, calculating the actual physical rotation angle of the first and second steering wheels based on the coordinates of the instantaneous rotation center in S134 includes:

[0139] Based on the coordinates of the instantaneous rotation center in the vehicle coordinate system, calculate the first vector pointing to the first steering wheel mounting point and the second vector pointing to the second steering wheel mounting point.

[0140] When the instantaneous rotation center is located to the left of the vector pointing from the second steering wheel mounting point to the first steering wheel mounting point, rotate the first vector / second vector counterclockwise by 90° to obtain the direction vector of the corresponding steering wheel;

[0141] When the instantaneous rotation center is located to the right of the vector pointing from the second steering wheel mounting point to the first steering wheel mounting point, rotate the first vector / second vector clockwise by 90°, or add π to the direction vector after rotating it counterclockwise by 90° to obtain the direction vector of the corresponding steering wheel.

[0142] Based on the direction vector, the actual physical rotation angle is calculated using the arctangent function and normalized to the interval (-π, π] to obtain the actual physical rotation angle of the first and second steering wheels.

[0143] This embodiment is based on rigid body planar kinematics and uses the geometric relationship between the instantaneous rotation center and the steering wheel mounting point to calculate the actual physical rotation angle of the steering wheel. Specifically, the calculation first constructs a vector pointing from the instantaneous rotation center to each steering wheel mounting point; then, based on the sign (counterclockwise or clockwise) of the AGV's rotation angle, this vector is rotated 90° counterclockwise or clockwise accordingly to obtain the steering wheel's velocity direction vector; finally, the angle of this direction vector is solved using the arctangent function and normalized to the interval (-π, π] to obtain a unique and continuous actual physical rotation angle.

[0144] This embodiment ensures that the steering wheel rotation direction is strictly consistent with the actual movement direction, avoiding 180° direction misjudgment and angle jump problems, providing a high-precision true value reference for zero position offset calculation, and significantly improving the reliability and accuracy of the entire zero position calibration process.

[0145] For example, in the AGV vehicle coordinate system, let the coordinates of the rear steering wheel (second steering wheel) mounting point B be (-0.5, 0), and the coordinates of the front steering wheel (first steering wheel) mounting point A be (0.5, 0). Therefore, the vector pointing from B to A... (Set as reference vector) = (1.0,0), which is along the positive X-axis of the vehicle body.

[0146] Scenario 1: Instantaneous rotation center at reference vector Left side (corresponding to left turn)

[0147] Suppose that the coordinates of the instantaneous rotation center C obtained by the solution are (0, 6).

[0148] Calculate the first vector C points to from A. =AC=(0.5-0,0-6)=(0.5,-6).

[0149] Determine the location: Point C(0,6) lies within the reference vector. Above (from (-0.5,0) to (0.5,0)), i.e. to the left.

[0150] At this time, Rotate 90° counterclockwise to obtain the direction vector of the first steering wheel (6, 0.5).

[0151] The angle is approximately 4.76°, calculated using atan2(y,x)=atan2(0.5,6).

[0152] Scenario 2: Instantaneous rotation center at reference vector Right side (corresponding to right turn)

[0153] Suppose that the coordinates of the instantaneous rotation center C obtained by the solution are (0, -6).

[0154] Calculate the first vector C points to from A. =AC=(0.5-0,0-(-6))=(0.5,6).

[0155] Determine the location: Point C(0,-6) lies within the reference vector. Below, that is, on the right.

[0156] At this point, you can choose to Rotate 90° clockwise, or add π to the result of rotating 90° counterclockwise.

[0157] First, rotate counterclockwise 90°: (-6, 0.5).

[0158] Adding π further: the direction vector of the first steering wheel is equivalent to (6, -0.5).

[0159] The angle is approximately -4.76°, calculated using atan2(y,x)=atan2(-0.5,6).

[0160] Using this method, regardless of whether the AGV turns left or right, the actual physical rotation angle of the steering wheel can be correctly calculated based on the geometric position of the instantaneous rotation center.

[0161] In one embodiment, the vehicle-mounted pose perception sensor installation angle calibration process in S3 includes one or more calibrations, and each calibration includes the following steps:

[0162] S31, after the zero-position compensation takes effect, a zero-reset command is sent to the steering drive of the first and second steering wheels so that the feedback measurement angles of the first and second steering wheels converge to the preset tolerance range centered on 0°.

[0163] S32, control the AGV to move forward a preset short distance and then stop, and continuously collect the pose data of the vehicle pose perception sensor during the driving process. The preset short distance satisfies the condition that the actual driving trajectory of the AGV can be approximated as a straight line under the condition that the feedback measurement angles of the first steering wheel and the second steering wheel are within the preset tolerance range.

[0164] S33, based on the position components in the collected pose data, perform linear fitting to obtain a fitted straight line, and calculate the actual driving direction angle of the AGV body according to the slope of the fitted straight line.

[0165] S34, calculate the arithmetic mean of the attitude angle components in the collected pose data to obtain the average azimuth angle of the vehicle pose perception sensor.

[0166] S35. Based on the difference between the average azimuth angle and the actual driving direction angle, determine the installation angle of the vehicle posture perception sensor in the vehicle coordinate system for this calibration.

[0167] This embodiment calibrates the installation angle of the vehicle-mounted posture perception sensor (such as a lidar) relative to the vehicle coordinate system by controlling a dual-steering-wheel AGV with calibrated zero position to perform a short linear motion. First, with zero-position compensation active, the system instructs the two steering wheels to return to center and confirms that their feedback angle is stable within a tolerance range near 0° to ensure the straightness of the travel trajectory. Then, the AGV travels forward a preset short distance while continuously collecting posture data output by the sensor. Based on the collected position point (x, y), the best-fitting straight line is obtained through linear least squares fitting, and the angle corresponding to its slope is the actual travel direction angle of the AGV. Simultaneously, the arithmetic mean of all attitude angle (heading angle) components is calculated to obtain the average azimuth angle reported by the sensor. Since the sensor is fixed to the vehicle body, the deviation between its average azimuth angle and the actual travel direction angle is its installation angle error; the difference between the two is the desired installation angle.

[0168] This embodiment cleverly utilizes the AGV's high-precision linear motion capability and the sensor's pose output to achieve self-calibration of the sensor's installation angle without any external reference or manual intervention. Linear fitting of position data effectively suppresses single-point positioning noise, and attitude angle averaging further improves the stability of angle estimation. Thus, while ensuring ease of operation, it achieves high-precision and robust automatic identification of installation parameters, significantly improving the positioning consistency and navigation reliability of the AGV system.

[0169] For example, an AGV travels forward 0.5 meters, recording 100 pose points. The straight line obtained after linear fitting is almost parallel to the x-axis, and α = 0.1° is calculated. Simultaneously, the average of the 100 attitude angles is 1.3°. Therefore, the sensor mounting angle β... inst =1.3° - 0.1° = 1.2°. This means that the sensor's perception of the front is actually 1.2° to the right of the vehicle's front.

[0170] In one embodiment, the vehicle-mounted pose perception sensor installation angle calibration process in S3 further includes:

[0171] The calibration process is repeated multiple times until a preset second termination condition is met. The average of all calibration results is then taken as the final installation angle of the vehicle-mounted pose sensing sensor.

[0172] The second termination condition includes: reaching the preset maximum number of calibrations, or the absolute difference between the installation angle of the vehicle pose perception sensor in the vehicle coordinate system obtained in the current calibration and the installation angle of the vehicle pose perception sensor in the vehicle coordinate system obtained in the previous calibration is less than the preset second convergence threshold.

[0173] This embodiment, based on the previous embodiment, introduces a multi-round iteration and convergence mechanism. It repeatedly executes the complete single calibration process (S31-S35) multiple times, obtaining an estimated installation angle each time. Then, it checks whether the absolute value of the difference between the current calibration result and the previous result is less than a preset second convergence threshold (e.g., 0.05°). If this threshold is met, or the maximum number of calibrations has been reached, the iteration stops, and the average of all calibration results is taken as the final installation angle.

[0174] This embodiment further improves the accuracy and reliability of sensor installation angle calibration. A single straight-line drive may be affected by factors such as minor ground undulations and instantaneous sensor drift. Through multiple repetitions and averaging, these random disturbances can be effectively smoothed out. The convergence judgment mechanism ensures that the calibration stops in a timely manner after the required accuracy is achieved, thus optimizing the calibration time.

[0175] For example, during sensor installation angle calibration, the first measurement yielded 1.25°, the second 1.18°, and the third 1.22°. The preset convergence threshold was 0.1°. The difference between the second and first measurements was 0.07°, which is less than the threshold, therefore the calibration ended. The final result was (1.25° + 1.18°) / 2 = 1.215°. This result is more reliable than any single measurement.

[0176] like Figure 2-5 As shown, in order to better understand the working principle of the automatic parameter calibration method for dual-steering wheel AGV of this application, the following is a complete flowchart illustrating the automatic parameter calibration method for dual-steering wheel AGV:

[0177] I. Calibration of steering wheel zero-position offset

[0178] Before starting calibration, park the AGV in an open area where the vehicle-mounted posture perception sensor can accurately locate it, ensuring that there are no obstacles during the AGV's operation.

[0179] 1. Record initial values ​​and set initial angles: Record the initial zero-position offset values ​​of the first and second steering wheels (usually 0 or the previous calibration value). Set an initial small angle with opposite signs for the first and second steering wheels (e.g., +5° and -5°) to avoid the AGV traveling in a purely straight line, allowing the travel trajectory to present a certain arc. Assume the initial angles of the first steering wheel (front wheel) and the second steering wheel (rear wheel) are θ. setf and θ setr , and θ setf =-θ setr ≠0.

[0180] 2. Acquire Starting Point Data: Set the number of pose sampling times to N (e.g., N=10), and begin acquiring the current pose data from the onboard pose sensing sensor. Stop after acquiring N pose data. Calculate the average of the heading angles from the N pose data acquisitions, and use this average as the starting heading angle φ. start Due to the presence of steering resistance, the steering wheel setting angle and the feedback measurement angle are usually not exactly the same. Therefore, the steering wheel feedback measurement angle at the initial moment is read and recorded, and denoted as θ. measf and θ measr .

[0181] 3. Issuing Driving Commands: The onboard controller issues slow-speed driving commands, controlling the AGV to travel forward or backward a set distance L (e.g., 1 meter). The AGV stops once either the first or second steering wheel reaches the set distance. The current calibration count is recorded starting from "1". An odd number of calibrations results in forward movement, while an even number results in backward movement. This ensures the AGV essentially travels back and forth between two points, saving space required for calibration and improving safety.

[0182] 4. Record endpoint data: After the AGV stops, record the actual distance traveled by the first and second steering wheels, denoted as d. f d r When the AGV moves forward, d f d r The value is positive; when the AGV moves backward, d... f d r The value is negative. Then, the pose data of the ending point is collected. After N collections, the collection stops, and the average value of the heading angle in the N poses is calculated as the ending heading angle φ. end .

[0183] 5. Calculate the calibration results:

[0184] 5.1. Determine the rotation radius of the front and rear steering wheels: Calculate the difference in heading angle between the starting and ending points, Δφ = φ end -φ startBecause the vehicle-mounted posture sensing sensor is fixedly mounted on the AGV body, based on the motion characteristics of a planar rigid body, this angular difference represents the angle the AGV body has rotated. A positive Δφ indicates the AGV is rotating counterclockwise, and a negative Δφ indicates the AGV is rotating clockwise. For example... Figure 2 As shown, C is the instantaneous center of rotation, xoy is the vehicle coordinate system, and A and B are the mounting points of the first steering wheel (front wheel) and the second steering wheel (rear wheel), respectively. Based on the characteristics of planar rigid body motion, the AGV rotates around the instantaneous center of rotation C throughout its movement from the starting point to the ending point. Assume the rotation radii of the first and second steering wheels are R... f R r Then we have: R f =d f / Δφ,R r =d r / Δφ.

[0185] 5.2. Find the instantaneous coordinates of the rotation center: e.g. Figure 3 As shown, assume that the coordinates of the steering wheel mounting points A and B in the vehicle coordinate system are (x, y, y) and (x, y, y) respectively. f ,y f ) and (x r ,y r Given that the radius of rotation R is... f R r The problem is transformed into finding the intersection point of two circles given their centers and radii. This involves solving the following system of equations: (xx) f )²+(yy f )²=R f ² and (xx) r )²+(yy r )²=R r ² gives the coordinates of the two intersection points.

[0186] 5.3 Determining if there is a valid intersection point: Let the vector pointing from the rear wheel to the front wheel be... R f and R r The notation remains the same without loss of generality, using R. f The symbol is used as a reference. When R f A value greater than 0 indicates that the instantaneous rotation center is on the vector. The left side; when R f When the value is less than 0, it indicates that the instantaneous rotation center is on the vector. To the right. Calculate the vector formed by the candidate intersection point P and the rear wheel B. and The cross product of R. If the cross product result is the same as R... f If the signs are the same, then the intersection point is a valid intersection point, and there will be at most one valid intersection point, which is the instantaneous rotation center point C (i.e., ...). Figure 3(P1 in the middle).

[0187] 5.4 Calculate the actual angle of the steering wheel: There are two cases:

[0188] First, define a vector from the second steering wheel mounting point (B) to the first steering wheel mounting point (A). This is the reference vector.

[0189] a) When the instantaneous rotation center C is located at the reference vector When the instantaneous rotation center point C is on the left, the vectors pointing from the instantaneous rotation center point C to the centers of the first and second steering wheels are respectively , At this point, the vector , Rotating each steering wheel 90 degrees counterclockwise yields its direction vector. Let the actual rotation angles of the first and second steering wheels be θ. actf and θ actr Then we have: θ actf =atan2(x f -x c , -(y f -y c )), θ actr =atan2(x r -x c , -(y r -y c )).

[0190] b) When the instantaneous rotation center C is located at the reference vector When the first and second steering wheels are on the right, add π to the angle obtained from the above formula to get the actual angles of the first and second steering wheels.

[0191] Finally, the calculated θ actf and θ actr Normalize to the interval (-π, π].

[0192] 5.5 Calculate the zero-position offset value: Let the zero-position offset values ​​of the first and second steering wheels be Δθ respectively. f , Δθ r Then: Δθ f =θ actf -θ measf , Δθ r =θ actr -θ measr .

[0193] 6. Repeat the second calibration: Enter the second calibration. In this calibration, the initial small angles set for the first and second steering wheels are the same as those in the first calibration, making it easier for the AGV to return from the stopping position at the end of the first calibration to the starting position at the end of the first calibration. Steps 1-6 complete two round trip calibrations, defined as one round of calibration.

[0194] 7. Calculate the calibration result of the current wheel: Take the average of the calibration results of the current wheel in two round trips as the calibration result of the current wheel.

[0195] 8. Repeat calibration multiple times: Repeat steps 1-7 to perform several new calibration cycles. The initial angle value can be different in each new calibration cycle.

[0196] 9. Calculate the final calibration result: Set a condition for ending the calibration. The ending condition can be reaching the maximum number of calibration rounds (e.g., 5 rounds), or the difference between the calibration result of the current round and the calibration result of the previous round being within the set threshold range (e.g., 0.1°). After n rounds of calibration, a total of n calibration values ​​are obtained. Calculate the average of these n values ​​as the final calibration result.

[0197] II. Calibration of the mounting angle of the vehicle-mounted pose sensing sensor

[0198] After calibrating the steering wheel zero-position offset value, save the value to the AGV controller and make it effective. Ensure that this calibration value has been applied by the system before calibrating the installation angle of the on-board posture perception sensor.

[0199] 1. Set the steering wheel angle to 0: The AGV controller sends control commands to the steering drive so that the feedback measurement angle of the first and second steering wheels is close to 0 degrees and within the allowable error threshold (e.g., ±0.5°).

[0200] 2. Issuing driving commands and collecting data: The onboard controller issues a slow-speed driving command, causing the AGV to move forward a short, predetermined distance (e.g., 0.5m). Simultaneously, the positioning results from the onboard posture sensing sensors are recorded during the driving process. Because the actual measured angle between the first and second steering wheels is nearly 0 degrees, the short-distance movement of the AGV can be approximated as straight-line travel.

[0201] 3. Calculate the AGV's heading angle: After reaching the set travel distance, the AGV stops. Because the onboard posture sensing sensor is fixed to the AGV body, the actual movement trajectory of the sensor within this short distance is also close to a straight line. Read the saved position values ​​(x, y, y) of all positioning postures. i ,y i This set of points forms a series of two-dimensional points. A linear least-squares fit is then performed on this set of points to obtain a fitted straight line. For example... Figure 4 As shown, the AGV's movement direction is consistent with the fitted straight line, and the angle between it and the x-axis of the global coordinate system is α, which is the actual driving direction angle of the AGV.

[0202] 4. Calculate the results of this calibration: Read the attitude angle values ​​ψ of all saved positioning poses. i Calculate its average value ψ avg This allows us to obtain the average azimuth angle of the vehicle-mounted pose perception sensor. For example... Figure 5 As shown, x L y L Let x be the sensor coordinate system. G y G Let x be the global coordinate system and xy be the vehicle body coordinate system. The sensor's azimuth angle in the global coordinate system equals the vehicle body's azimuth angle plus the sensor's mounting angle under the vehicle body. Therefore, the sensor's mounting angle under the vehicle body is: β. inst =ψ avg -α.

[0203] 5. Repeat calibration: Repeat steps 1-4 several times (e.g., 5 times).

[0204] 6. Calculate the final calibration result: Set a condition for ending the calibration. The ending condition can be reaching the maximum number of calibrations, or the difference between the current calibration result and the previous calibration result being within a set threshold range. After n calibrations, a total of n calibration values ​​are obtained. Calculate the average of these n values ​​as the final calibration result.

[0205] In summary, the automatic parameter calibration method for dual-steering wheel AGVs provided in this application, by cleverly utilizing the kinematic characteristics and posture perception capabilities of the AGV itself, achieves fully automatic and high-precision calibration of key physical parameters, demonstrating significant technological advancement and practical value.

[0206] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0207] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0208] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0209] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for automatic parameter calibration of a dual-steering wheel AGV, characterized in that, The method includes the following steps: S1, perform a zero-position offset calibration process on the first and second steering wheels of the target dual-steering-wheel AGV to obtain the zero-position offset values ​​of the first and second steering wheels, wherein, The zero-position offset calibration process includes one or more calibration rounds, wherein each calibration round includes two unidirectional movements in opposite directions, denoted as the first unidirectional movement and the second unidirectional movement, respectively. The first unidirectional motion performs the following steps: S11, when the AGV is stationary, set the initial setting angle of the first steering wheel and the initial setting angle of the second steering wheel, read the real-time angle feedback value output by the steering drive corresponding to the first steering wheel and the second steering wheel as the feedback measurement angle, and collect the starting heading angle. S12, control the AGV to travel a set distance in the first direction, stop when either steering wheel reaches the set distance, record the actual travel distance of the first and second steering wheels, and collect the ending heading angle; S13, based on the starting heading angle, ending heading angle, actual travel distance of the first and second steering wheels, and feedback measurement angles of the first and second steering wheels, calculate the zero-position offset value of the first and second steering wheels corresponding to this unidirectional movement. The second unidirectional motion performs the following steps: S14, when the AGV is stationary at the end position of the first unidirectional motion, keep the first steering wheel and the second steering wheel at the same initial set angle as the first unidirectional motion, read the real-time angle feedback value output by the steering drive corresponding to the first steering wheel and the second steering wheel as the feedback measurement angle, and collect the starting heading angle; S15, control the AGV to travel a set distance in the opposite direction to the first direction, stop when either steering wheel reaches the set distance, record the actual travel distance of the first steering wheel and the second steering wheel, and collect the ending heading angle; S16. Based on the starting heading angle, the ending heading angle, the actual travel distance of the first steering wheel and the second steering wheel, and the feedback measurement angle of the first steering wheel and the second steering wheel, calculate the zero offset value of the first steering wheel and the zero offset value of the second steering wheel corresponding to this unidirectional movement. S2, write the zero offset value of the first steering wheel and the zero offset value of the second steering wheel into the AGV controller to perform zero-position compensation for the steering wheel steering command or steering wheel feedback angle. S3, after the zero-position compensation takes effect, the vehicle-mounted pose sensing sensor installation angle calibration process is executed to obtain the installation angle of the vehicle-mounted pose sensing sensor in the vehicle coordinate system, wherein... The calibration process for the installation angle of the vehicle-mounted pose sensing sensor includes one or more calibrations, and each calibration includes the following steps: S31, after the zero-position compensation takes effect, a zero-reset command is sent to the steering drive of the first steering wheel and the second steering wheel so that the feedback measurement angles of the first steering wheel and the second steering wheel converge to a preset tolerance range centered on 0°. S32, control the AGV to travel forward a preset short distance and then stop, and continuously collect the pose data of the vehicle pose perception sensor during the travel process. The preset short distance satisfies the condition that the actual travel trajectory of the AGV can be approximated as a straight line when the feedback measurement angle of the first steering wheel and the second steering wheel is within the preset tolerance range. S33, Based on the position components in the collected pose data, perform linear fitting to obtain a fitted straight line, and calculate the actual driving direction angle of the AGV body according to the slope of the fitted straight line. S34, calculate the arithmetic mean of the attitude angle components in the collected pose data to obtain the average azimuth angle of the vehicle pose sensing sensor; S35, based on the difference between the average azimuth angle and the actual driving direction angle, determine the installation angle of the vehicle posture perception sensor in the vehicle coordinate system for this calibration.

2. The automatic parameter calibration method for a dual-steering wheel AGV according to claim 1, characterized in that, The zero-position compensation for the steering wheel steering command or steering wheel feedback angle in S2 includes: When sending a steering command to the steering wheel, the target steering angle is corrected based on the zero-position offset values ​​of the first and second steering wheels; or, When reading the steering wheel feedback angle, the feedback angle is corrected based on the zero-position offset values ​​of the first and second steering wheels.

3. The automatic parameter calibration method for a dual-steering wheel AGV according to claim 2, characterized in that, The zero-offset calibration process in S1 also includes: S17, take the average of the zero offset values ​​of the two first steering wheels and the two second steering wheels obtained from two unidirectional movements in opposite directions during the calibration of the same wheel, and use them as the zero offset values ​​of the first steering wheel and the second steering wheel for calibration in this round. S18, repeat the calibration multiple times until the preset first termination condition is met, and take the average of the zero-position offset values ​​of the first steering wheel and the second steering wheel obtained from all calibration rounds as the final zero-position offset values ​​of the first steering wheel and the second steering wheel. The first termination condition includes: reaching the preset maximum number of calibration wheels, or the difference between the zero offset value of the first steering wheel obtained by the current calibration and the zero offset value of the first steering wheel obtained by the previous calibration, and the difference between the zero offset value of the second steering wheel obtained by the current calibration and the zero offset value of the second steering wheel obtained by the previous calibration are all less than the preset first convergence threshold.

4. The automatic parameter calibration method for a dual-steering wheel AGV according to claim 1, characterized in that, The initial setting angles of the first steering wheel and the second steering wheel are a pair of non-zero angles of equal magnitude and opposite sign, so that the AGV generates a heading angle change during driving that can be distinguished by the on-board posture sensing sensor. The absolute value of the initial set angle is greater than 0° and does not exceed a first preset threshold. The first preset threshold is determined based on at least one of the AGV's wheelbase, maximum allowable turning radius, or calibrated site dimensions.

5. The automatic parameter calibration method for a dual-steering wheel AGV according to claim 1, characterized in that, The starting heading angle and the ending heading angle are both obtained by arithmetically averaging the heading angle components in N consecutive pose data acquisitions from the vehicle-mounted pose perception sensor, where N is an integer greater than 1.

6. The automatic parameter calibration method for a dual-steering wheel AGV according to claim 1, characterized in that, The calculation of the zero-position offset values ​​of the first and second steering wheels corresponding to this unidirectional movement, based on the initial heading angle, the final heading angle, the actual travel distance of the first and second steering wheels, and the feedback measurement angles of the first and second steering wheels, includes: S131, Calculate the angle turned by the AGV body in this unidirectional movement based on the difference between the starting heading angle and the ending heading angle; S132, Based on the angle turned by the AGV body in this unidirectional movement and the actual travel distance of the first steering wheel and the second steering wheel, calculate the rotation radius of the first steering wheel and the second steering wheel respectively; S133, based on the rotation radius of the first and second steering wheels and the coordinates of the mounting points of the first and second steering wheels in the vehicle coordinate system, solve for the intersection of two circles with the two mounting points as centers and the corresponding rotation radii as radii, and select the unique and effective instantaneous rotation center. S134, Calculate the actual physical rotation angle of the first and second steering wheels based on the coordinates of the instantaneous rotation center; S135, the actual physical rotation angles of the first and second steering wheels are subtracted from the corresponding feedback measurement angles to obtain the zero-position offset values ​​of the first and second steering wheels corresponding to this unidirectional movement.

7. The automatic parameter calibration method for a dual-steering wheel AGV according to claim 6, characterized in that, The calculation of the actual physical rotation angle of the first and second steering wheels based on the coordinates of the instantaneous rotation center in S134 includes: Based on the coordinates of the instantaneous rotation center in the vehicle coordinate system, calculate the first vector pointing to the first steering wheel mounting point and the second vector pointing to the second steering wheel mounting point from the instantaneous rotation center. When the instantaneous rotation center is located to the left of the vector pointing from the second steering wheel mounting point to the first steering wheel mounting point, the first vector / second vector is rotated counterclockwise by 90° to obtain the direction vector of the corresponding steering wheel; When the instantaneous rotation center is located to the right of the vector pointing from the second steering wheel mounting point to the first steering wheel mounting point, rotate the first vector / second vector clockwise by 90°, or add π to the direction vector after rotating it counterclockwise by 90° to obtain the direction vector of the corresponding steering wheel; Based on the direction vector, the actual physical rotation angle is calculated using the arctangent function and normalized to the interval (-π, π] to obtain the actual physical rotation angle of the first and second steering wheels.

8. The automatic parameter calibration method for a dual-steering wheel AGV according to any one of claims 1-7, characterized in that, The vehicle-mounted pose perception sensor installation angle calibration process in S3 also includes: The calibration process is repeated multiple times until a preset second termination condition is met. The average of all calibration results is then taken as the final installation angle of the vehicle-mounted pose sensing sensor. The second termination condition includes: reaching the preset maximum number of calibrations, or the absolute difference between the installation angle of the vehicle pose perception sensor in the vehicle coordinate system obtained in the current calibration and the installation angle of the vehicle pose perception sensor in the vehicle coordinate system obtained in the previous calibration is less than the preset second convergence threshold.

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