An adaptive steering calibration method for outdoor unmanned sweepers

Abstract

The present invention belongs to the technical field related to vehicle control, and specifically is an adaptive steering calibration method for an outdoor unmanned sweeper, comprising the following steps: obtaining a calibration starting point and a calibration baseline based on the onboard GNSS_INS system of the outdoor unmanned sweeper; generating a steering calibration angle set based on the known vehicle steering angle and divided into equal intervals; issuing a control instruction to the vehicle to obtain the coordinate value of the center point of the vehicle's rear axle, adding it to the set of travel trajectory points, fitting the turning radius corresponding to this set of steering angles based on the recorded set of travel trajectory points, and calculating and recording the actual steering angle. Repeat the above steps until all steering angles in the preset steering calibration angle set are calibrated, and then fit the calibration curve between the preset steering angle and the actual steering angle to obtain a cubic relationship function between the two. This calibration method is simple and reliable, and can ensure the steering control accuracy of the vehicle when performing complex actions such as edge cleaning.

Description

Technical Field

[0001] The present invention mainly relates to the technical fields related to vehicle control and automatic driving, and specifically provides an adaptive steering calibration method for outdoor unmanned sweepers, which is suitable for controlling unmanned sweepers in complex operating scenarios such as urban sanitation and industrial parks. Background Art

[0002] In practice, unmanned outdoor road sweepers operate across a wide range of environments, including urban roads, residential areas, parks, and industrial parks. They often encounter complex scenarios such as narrow roads and sharp turns. Furthermore, due to road design, garbage is more likely to accumulate near curbs on both sides of the road when cleaning urban roads, necessitating close-to-the-edge cleaning by the sweepers. All of these situations place extremely high demands on the path planning and steering control precision of unmanned outdoor road sweepers.

[0003] To improve vehicle steering control accuracy, the current common practice is to perform steering calibration on each vehicle individually after it leaves the factory. This is done by installing a 6-axis gyroscope on the front steering wheel axle. After the front wheel rotates according to the set angle, the actual steering angle output by the gyroscope is recorded, thereby obtaining the error between the preset steering angle and the actual steering angle. By repeating the above steps multiple times, it is ensured that the angle covers the entire range from 0 degrees to the maximum steering angle. This process is extremely cumbersome and requires manual operation step by step. Furthermore, gyroscopes are not standard equipment for outdoor unmanned road sweepers and require additional configuration. Furthermore, since the steering angle of the front wheel is recorded directly, the gyroscope needs to be installed on the steering wheel. The installation error of the gyroscope and its own temperature drift error will directly affect the accuracy of the steering calibration. Summary of the Invention

[0004] To address the shortcomings of current technology, the present invention combines existing technologies and, based on practical applications, provides an adaptive steering calibration method for an outdoor unmanned sweeper to ensure the steering control accuracy of the vehicle when performing complex actions such as edge sweeping.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for adaptive steering calibration of an outdoor unmanned sweeper comprises the following steps:

[0007] S1. Based on the onboard GNSS_INS system of the outdoor unmanned sweeper, the position and attitude values ​​of the center point of the vehicle's rear axle are obtained as the calibration starting point. A straight line is adaptively generated along the extension line of the vehicle's rear axle as the subsequent calibration reference line;

[0008] S2. Generate a set of steering calibration angles based on the known maximum left and right steering angles of the vehicle's front wheels, divided into equal intervals;

[0009] S3. Send control commands to the vehicle and obtain the coordinates of the vehicle's rear axle center point in real time at a set frequency. These coordinates are added to the set of travel trajectory points. When the vehicle reaches the calibration baseline, the sending of control commands stops. Based on the recorded travel trajectory points, the turning radius corresponding to the current set of steering angles is fitted. The actual steering angle is calculated and recorded, and the next set of control commands is switched.

[0010] S4. Repeat step S3 until all steering angles in the preset steering calibration angle set are calibrated. Then, based on the actual steering angle set calculated in the above process, a calibration curve between the preset steering angle and the actual steering angle is fitted to obtain a cubic relationship function between the two.

[0011] Furthermore, step S1 specifically includes:

[0012] S11. Turn the front steering wheel of the unmanned sweeper to zero position and check the working status of the GNSS_INS system to confirm that it is working properly.

[0013] S12. The vehicle controller reads the position and attitude values ​​output by the GNSS_INS system, projects the GNSS_INS installation position relative to the center point of the vehicle's rear axle to obtain new position and attitude values, and uses these values ​​as the starting point for calibration.

[0014] S13. Generate a straight line from the vehicle calibration starting point along the extension line of the rear wheel axle of the vehicle, which serves as a calibration reference line for subsequent calibration.

[0015] Furthermore, step S2 specifically includes: after determining that the number of groups that need to be calibrated is n, based on the known maximum left steering angle of the vehicle's front wheels, generating a left steering calibration angle set at equal intervals in the interval [0, maximum left steering angle], and similarly generating a right steering calibration angle set, and merging the left and right steering calibration angle sets into a steering calibration angle set.

[0016] Further, step S3 specifically includes:

[0017] S31, issuing a control instruction to the vehicle, wherein the control instruction includes a fixed speed value and the value of the steering calibration angle set generated in step S2,

[0018] S32. While the vehicle is moving, the coordinates of the center point of the vehicle's rear axle are obtained in real time at a set frequency. The coordinates and attitude of the center point of the rear axle are converted from the original output values ​​of the GNSS_INS system and added to the trajectory point set.

[0019] S33, during the vehicle's travel, after obtaining the coordinate value of the center point of the vehicle's rear axle, determine whether it has reached the calibration reference line based on the value;

[0020] S34. If the vehicle reaches the calibration baseline, stop issuing control commands and fit the turning radius corresponding to the steering angle of the current set based on the recorded trajectory points. The trajectory of the vehicle running according to the control command will be a semicircular arc. The Pratt algorithm is used to fit the circle radius and obtain the turning radius value.

[0021] S35. Obtain a turning radius value, and calculate an actual steering angle based on a relationship between the turning radius and the steering angle;

[0022] S36. After calculating the actual steering angle, add the actual steering angle to the actual steering angle set and switch to the next set of control instructions.

[0023] Furthermore, in step S33 , the basis for determining whether the vehicle has reached the calibration reference line is that the Euclidean distance from the vehicle coordinate point to the reference line is less than a set threshold.

[0024] Furthermore, in step S4, a calibration curve between the preset steering angle and the actual steering angle is fitted by the least square method to obtain a cubic relationship function between the two.

[0025] Beneficial effects of the present invention:

[0026] The present invention uses the vehicle's own GNSS_INS system to capture the motion trajectory of an outdoor unmanned road sweeper in real time. By equally dividing the left and right steering angles, a set of all steering angles that require calibration is obtained. Simultaneously, a vehicle calibration reference line is automatically generated based on the vehicle's initial position and posture. After an automatic control command is issued, the vehicle begins autonomous movement. When the vehicle reaches the calibration reference line, the calibration of that group of steering angles is considered complete, and the next group of steering angles is switched to. After all steering angles have been calibrated, a cubic polynomial function representing the correspondence between the preset steering angle and the actual steering angle is automatically calculated. This method fully utilizes the GNSS_INS system configured on the outdoor unmanned road sweeper, eliminating the need for additional sensors as a calibration reference. After setting the maximum left and right steering angles, the calibration process is automatically completed, significantly reducing the workload of manual calibration. Furthermore, by sampling more steering angle groups, the angle fitting accuracy can be effectively improved, thereby ensuring the steering control accuracy of the vehicle when performing complex actions such as edge cleaning. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Detailed flow chart of the present invention.

[0028] Figure 2 Schematic diagram illustrating the steering angle of the present invention.

[0029] Figure 3 Schematic diagram of vehicle coordinate conversion according to the present invention.

[0030] Figure 4 This is a schematic diagram of the calibration baseline automatically generated by the present invention.

[0031] Figure 5 Schematic diagram of steering angle calculation of the present invention.

[0032] Figure 6 Schematic diagram of curve fitting between the preset steering angle and the actual steering angle of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the contents of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the present application.

[0034] This embodiment provides an adaptive steering calibration method for an outdoor unmanned sweeper. After obtaining the real-time position and posture of the unmanned sweeper through the vehicle's GNSS_INS system, a calibration baseline is adaptively generated to automatically complete the calibration of multiple groups of steering. After the calibration is completed, a cubic curve function between the preset steering angle and the actual steering angle is automatically generated. Figure 1 As shown, the specific technical solution of this embodiment includes the following steps:

[0035] S1. Output position and attitude values ​​of the onboard GNSS_INS system of the outdoor unmanned sweeper , the position and attitude value of the rear axle center point are obtained by coordinate translation Using this point as the calibration starting point, a straight line is adaptively generated along the extension line of the rear wheel axle as the subsequent calibration reference line. Specifically, S11: The unmanned sweeper is parked in an open outdoor environment, the front steering wheel is turned back to zero, and the GNSS_INS system working status is checked to confirm that it is working properly.

[0036] S12. Reference Figure 3 As shown, the vehicle controller reads the position and attitude values ​​output by the GNSS_INS system , GNSS_INS system usually uses the Northeast Sky coordinate system, is the position in the northeast celestial coordinate system, The vehicle's attitude and orientation. Based on the GNSS_INS installation position relative to the center of the rear axle (delta_x, delta_y) , projected to the center point of the rear axle to obtain the new position and attitude value , and use this value as the starting point for calibration. The calculation formula is as follows:

[0037] ,

[0038] ;

[0039] S13, Reference Figure 4 As shown, from the vehicle calibration starting point Generate a straight line along the extension line of the rear wheel axle of the vehicle, which will be used as the reference line for subsequent calibration. ， 、 straight line The direction of this line in the GNSS_INS coordinate system is 90° , passing the vehicle calibration starting point .

[0040] The above steps determine the calibration starting point and calibration baseline for subsequent steering calibration.

[0041] S2. Generate a steering angle calibration set based on the known maximum steering angles of the vehicle's front wheels to the left and right, divided into equal intervals . Specifically including:

[0042] Determine the number of groups that need to be calibrated n After group ( n is an even number), based on the known maximum left steering angle of the vehicle's front wheels, a set of left steering calibration angles is generated at equal intervals in the interval [0, maximum left steering angle] Similarly, based on the known maximum right steering angle of the vehicle's front wheels, a right steering calibration set is generated at equal intervals in the interval [0, maximum right steering angle] Merge the left and right turn calibration sets into .

[0043] S3. Send control instructions to the vehicle , and obtain the coordinate value of the vehicle's rear axle center point in real time according to the set frequency , add it to the set of travel trajectory points. When it is detected that the vehicle reaches the calibration baseline, stop issuing control instructions, and according to the recorded travel trajectory point set { }, fitting the turning radius corresponding to this group of steering angles , calculate and record the actual steering angle , and switch to the next set of control instructions at the same time . Specifically including:

[0044] S31. Sending control instructions to the vehicle ,in speed It is a fixed speed value. To ensure a smaller positioning error during travel, it can usually be set to 0.2~0.5 m / s; The steering calibration angle set generated in step S2 value, i Start from 1.

[0045] S32: During the vehicle's movement, the coordinates of the vehicle's rear axle center point are obtained in real time according to the set frequency. , the value is the same as step S12, which is converted from the original output value of GNSS_INS to the coordinates and attitude of the rear axle center point and added to the trajectory point set { }.

[0046] S33, obtaining coordinate values ​​during vehicle movement Then, the value is used to determine whether the calibration baseline generated in step S13 is reached. The judgment basis is that the Euclidean distance from the vehicle coordinate point to the baseline is less than , the formula is as follows:

[0047] .

[0048] S34, if the vehicle reaches the calibration baseline, stop issuing control instructions, according to the recorded travel trajectory point set { }, fitting the turning radius corresponding to this group of steering angles . Follow the control instructions The trajectory of the running vehicle will be a semicircular arc. The pratt algorithm can be used to fit the circle radius and obtain the turning radius. The Pratt algorithm is a commonly used method for fitting circles to scattered points that is robust to noise and suitable for large curvatures.

[0049] S35, Reference Figure 5 As shown, get the turning radius The actual steering angle is calculated based on the relationship between the turning radius and the steering angle. , the calculation formula is as follows:

[0050] .

[0051] S36, calculating the actual steering angle After completion, Add to the actual steering angle set and switch to the next set of control instructions .

[0052] S4, repeat step S3 until the preset steering angle is set All steering angles are calibrated, and then the actual steering angle set calculated in the above process is , fitting the calibration curve between the preset steering angle and the actual steering angle (reference Figure 6 As shown), we get the cubic relationship function between the two , a, b, c, d is the corresponding coefficient of the function. Generally speaking, n The value will be greater than 4, so the preset steering angle set and the actual steering angle set The relationship between them was fitted using the least squares method, and we got Relationship function, the entire calibration process is completed.

[0053] During the autonomous driving process, if the front wheels need to reach a specific steering angle , just need to be substituted into the above relationship to obtain the corresponding preset steering angle That's it.

[0054] The method provided in this embodiment fully utilizes the GNSS_INS system equipped on the outdoor unmanned sweeper, eliminating the need for additional sensors as a calibration reference. After setting the maximum left and right steering angles, the above calibration process can be completed automatically, greatly reducing the workload of manual calibration. In addition, by sampling more steering angle groups, the angle fitting accuracy can be effectively improved, thereby ensuring the steering control accuracy of the vehicle when performing complex actions such as edge cleaning.

Claims

1. An adaptive steering calibration method for an outdoor unmanned sweeper, characterized in that: The steps include: S1. Based on the onboard GNSS_INS system of an outdoor unmanned road sweeper, the position and attitude values ​​of the center point of the vehicle's rear axle are obtained as the calibration starting point. A straight line is adaptively generated along the extension line of the vehicle's rear axle as the subsequent calibration reference line, specifically including: S11. Turn the front steering wheel of the unmanned sweeper to zero position and check the working status of the GNSS_INS system to confirm that it is working properly. S12. The vehicle controller reads the position and attitude values ​​output by the GNSS_INS system, projects the GNSS_INS installation position relative to the center point of the vehicle's rear axle to obtain new position and attitude values, and uses these values ​​as the starting point for calibration. S13, generating a straight line from the vehicle calibration starting point along the extension line of the rear wheel axle of the vehicle, which serves as a calibration reference line for subsequent calibration; S2. Generate a set of steering calibration angles based on the known maximum left and right steering angles of the vehicle's front wheels, divided into equal intervals; S3. Send control commands to the vehicle and obtain the coordinates of the vehicle's rear axle center point in real time at a set frequency. These coordinates are added to the set of travel trajectory points. When the vehicle reaches the calibration baseline, the sending of control commands stops. Based on the recorded travel trajectory points, the turning radius corresponding to the current set of steering angles is fitted. The actual steering angle is calculated and recorded, and the next set of control commands is switched. S4. Repeat step S3 until all steering angles in the preset steering calibration angle set are calibrated. Then, based on the actual steering angle set calculated in the above process, a calibration curve between the preset steering angle and the actual steering angle is fitted to obtain a cubic relationship function between the two.

2. The adaptive steering calibration method for an outdoor unmanned sweeper according to claim 1 is characterized in that: Step S2 specifically includes: after determining that the number of groups that need to be calibrated is n, based on the known maximum left steering angle of the vehicle's front wheels, generating a left steering calibration angle set at equal intervals in the interval [0, maximum left steering angle], and similarly generating a right steering calibration angle set, and merging the left and right steering calibration angle sets into a steering calibration angle set.

3. The adaptive steering calibration method for an outdoor unmanned sweeper according to claim 1 is characterized in that: Step S3 specifically includes: S31, issuing a control instruction to the vehicle, wherein the control instruction includes a fixed speed value and the value of the steering calibration angle set generated in step S2, S32. While the vehicle is moving, the coordinates of the center point of the vehicle's rear axle are obtained in real time at a set frequency. The coordinates and attitude of the center point of the rear axle are converted from the original output values ​​of the GNSS_INS system and added to the trajectory point set. S33, during the vehicle's travel, after obtaining the coordinate value of the center point of the vehicle's rear axle, determine whether it has reached the calibration reference line based on the value; S34. If the vehicle reaches the calibration baseline, stop issuing control commands and fit the turning radius corresponding to the steering angle of the current set based on the recorded trajectory points. The trajectory of the vehicle running according to the control command will be a semicircular arc. The Pratt algorithm is used to fit the circle radius and obtain the turning radius value. S35. Obtain a turning radius value, and calculate an actual steering angle based on a relationship between the turning radius and the steering angle; S36. After calculating the actual steering angle, add the actual steering angle to the actual steering angle set and switch to the next set of control instructions.

4. The adaptive steering calibration method for an outdoor unmanned sweeper according to claim 3 is characterized in that: In step S33 , whether the vehicle has reached the calibration reference line is determined based on whether the Euclidean distance from the vehicle coordinate point to the reference line is less than a set threshold.

5. The adaptive steering calibration method for an outdoor unmanned sweeper according to claim 1 is characterized in that: In step S4, a calibration curve between the preset steering angle and the actual steering angle is fitted by the least square method to obtain a cubic relationship function between the two.

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