Low-speed delivery robot motion control method

Abstract

The application discloses a low-speed distribution robot motion control method, realizes electromagnetic parking, in-place rotation, omni-directional translation and four-wheel steering motion mode, robot flexibility is greatly improved, and can cope with narrow limited space. The vehicle body motion mathematical model is constructed, specifically: four-wheel positions are A~D four points, the front-wheel axis center position is E point, the plane rectangular coordinate system origin is located at the whole vehicle center O point, and the steering instantaneous center point P is set on the X axis. In the absence of any motion instruction, the electromagnetic parking mode is entered. In the omni-directional translation mode, the deflection angles of the four steering motors are rad_e. In the in-place rotation mode, the four points all make circular motion with O as the center, and the turning radii are all the same. In the four-wheel steering mode, all mass points on the robot simultaneously make circular motion with P point as the center in the turning process, the direction vectors corresponding to the four points are determined, and the rotation speed values of the four-point driving motors and the deflection angle values of the steering motors are set.

Description

Technical Field

[0001] This invention relates to the field of robotics, and more specifically to a motion control method for a low-speed delivery robot. Background Technology

[0002] Currently, with the increasing maturity of new technologies such as autonomous driving, AI, and 5G, e-commerce platforms and express delivery companies have launched "contactless delivery," and unmanned delivery robots have appeared on the streets.

[0003] Robots deliver goods autonomously, avoiding human contact, and are highly efficient and low-cost, making them popular with courier companies and consumers. Meanwhile, the demand for last-mile delivery is also increasing, making unmanned delivery at the last mile a major future trend for delivery robots.

[0004] Currently, the movement mode used in delivery robots generally adopts a four-wheel driving mode, with a speed not exceeding 2m / s. The front wheels drive the front wheels and steer, or the rear wheels drive the front wheels and steer. The power is driven by a single drive motor. Turning is achieved by a central steering mechanism, which relies on a mechanical differential to match the speed of the left and right side wheels to meet the speed difference caused by turning.

[0005] The aforementioned common delivery robots have complex chassis mechanical structures (requiring differential design), limited movement modes (only forward or backward movement), and during turns, the steering center point is generally located on the rear axle, requiring a large turning radius. When fully loaded with goods, relying solely on differential turning can cause severe wheel wear. Furthermore, when performing door-to-door or indoor deliveries, their movement is restricted in confined spaces such as elevators and hallways, failing to meet delivery needs. Moreover, since only the front or rear wheels are driven, if a wheel without drive capability falls into a pothole, the entire vehicle will be unable to move forward.

[0006] Therefore, it is evident that current low-speed delivery robots are inadequate for working in limited spaces such as indoors. Summary of the Invention

[0007] In view of this, the present invention provides a motion control method for a low-speed delivery robot, which realizes electromagnetic parking, in-situ rotation, omnidirectional translation and four-wheel steering, greatly improving the flexibility of the robot and enabling it to cope well with narrow and limited spaces.

[0008] To achieve the above objectives, the technical solution of the present invention includes the following steps:

[0009] A mathematical model of vehicle motion is constructed as follows: the four wheel positions are A, B, C, and D, and the center position of the front wheel axis is E, which is used as the point for introducing the vehicle motion parameters, including the angle value rad_e and the speed value ve; L1 and L2 are the front and rear wheelbases and the wheel spacing on both sides, respectively; the origin of the plane rectangular coordinate system is located at the center point O of the vehicle, and the instantaneous center of rotation P is set on the X-axis.

[0010] Without any movement command issued, it defaults to electromagnetic parking mode.

[0011] When entering omnidirectional translation mode, the deflection angle of all four steering motors is rad_e, with a value range of:

[0012] When entering the stationary rotation mode, points A, B, C, and D all move in circles with O as the center. Their turning radii are all the same, so their corresponding turning angles are also the same.

[0013] When entering four-wheel steering mode, all the mass points on the robot simultaneously make circular motions around point P as the center during the turning process. Therefore, the magnitude and direction of the angular velocity ω are the same. Determine the direction vectors corresponding to points A, B, C, and D, and set the speed values ​​of the drive motors and the deflection angle values ​​of the steering motors at the four points A, B, C, and D.

[0014] Furthermore, in the absence of any movement commands, it defaults to electromagnetic parking mode, specifically as follows:

[0015] In electromagnetic parking mode, the speed of all four drive motors is 0 r / min; the steering direction at points A and D is counterclockwise, and the steering direction at points B and C is clockwise, with all steering angles set to 0.

[0016] Furthermore, when entering omnidirectional translation mode, the deflection angle of all four steering motors is rad_e, with a value range of: Specifically:

[0017] The speed values ​​of the four drive motors are all converted from ve (m / s). d is the diameter of the drive motor hub.

[0018] Furthermore, when entering the stationary rotation mode, in this mode, points A, B, C, and D all move in circles with O as the center, and their turning radii are all the same, so the corresponding turning angles are also the same. Specifically:

[0019] The established mathematical model of motion shows that... In this mode, points A, B, C, and D all move in circles with center O. Since their turning radii are all the same, their corresponding turning angles are also the same. Points A and D rotate clockwise, while points B and C rotate counterclockwise. The speed values ​​of the four drive motors remain the same, all calculated from ve. Points A and C are driven forward or backward, while points B and D are driven backward or forward, thus achieving overall clockwise or counterclockwise rotation in place.

[0020] Furthermore, the four-wheel steering mode specifically includes right turn and left turn processes:

[0021] During the right turn, achievable achievable During the turn, all the particles on the robot simultaneously move in a circle with point P as the center. Therefore, the magnitude and direction of the angular velocity ω are the same. From the velocity value ve at point E, the length of PE, and the right-hand rule, the space vector of the angular velocity can be obtained. achievable Using a unit vector perpendicular to the plane of motion, we can obtain The linear velocity at point A is the speed of the wheel, and the direction is the required steering angle. Similarly, the direction vectors corresponding to points B, C, and D can be obtained, and then the rotational speed of the drive motors and the deflection angle of the steering motors at points A, B, C, and D can be obtained. The steering at points A and B is clockwise, and the steering at points C and D is counterclockwise. The driving directions of the four points are all the same.

[0022] During the left turn, rad_p = rad_e. achievable achievable During the turn, all the particles on the robot simultaneously move in a circle with point P as the center. Therefore, the magnitude and direction of the angular velocity ω are the same. From the velocity value ve at point E, the length of PE, and the right-hand rule, the space vector of the angular velocity can be obtained. achievable Using a unit vector perpendicular to the plane of motion, we can obtain The linear velocity at point A is the speed of the wheel, and the direction is the required steering angle. Similarly, the direction vectors corresponding to points B, C, and D can be obtained, and then the rotational speed of the drive motors and the deflection angle of the steering motors at points A, B, C, and D can be obtained. The steering at points A and B is counterclockwise, and the steering at points C and D is clockwise. The driving directions of the four points are all the same.

[0023] Beneficial effects:

[0024] 1. The model created in this invention, based on the control of four-wheel drive and four-wheel steering motion, can be intuitively approximated as a common kinematic bicycle model by setting the input parameter point E. This makes it easier for control personnel to understand the model and get started quickly. Setting the instantaneous steering center point on the X-axis reduces the turning radius and facilitates the expansion of the four-wheel motion model, enabling electromagnetic parking, stationary rotation, omnidirectional translation, and four-wheel steering motion. This significantly improves the robot's flexibility and allows it to cope well with confined spaces.

[0025] 2. The main purpose of this invention is to address the shortcomings of delivery robots in limited indoor spaces, by providing a four-wheel steering and four-wheel drive motion control method. Instead of a single drive motor and steering motor for the entire vehicle, this method equips each wheel with an independent steering and drive motor. Through a motion mathematical model, using the center point of the front axis as the parameter input point (traveling speed, turning angle), the rotational speeds of the four drive motors and the deflection angles of the four steering motors are calculated. This enables electromagnetic parking, stationary rotation, omnidirectional translation, and four-wheel steering, significantly improving the robot's flexibility and allowing it to effectively handle confined spaces, meeting the needs of last-mile delivery. It also reduces wheel friction on the ground, simplifies the mechanical design, and lowers operating and maintenance costs. Because each of the four wheels is equipped with an independent high-power drive motor, it possesses excellent obstacle-avoidance capabilities when facing complex and uneven road surfaces, and its load-bearing capacity is significantly improved.

[0026] 3. The control mode involved in this invention also has strong expansion capabilities, allowing for the addition of six-wheel drive from a four-wheel base. Since the instantaneous steering center point is set on the vehicle's central X-axis, the two additional wheels can be installed at points M and N, the center positions of the front and rear wheels on the left and right sides, respectively. This ensures that the speed direction of the two newly added wheels is always perpendicular to the turning radii MP and NP, eliminating the need for steering during turns; only speed difference matching is required. This addition of two steering-free motors reduces cost and operational complexity while significantly improving driving capability, further meeting the needs of applications with larger loads and more complex road conditions. Attached Figure Description

[0027] Figure 1 This is a mathematical model diagram of the overall motion of the low-speed delivery robot in an embodiment of the present invention;

[0028] Figure 2 This is a mathematical model diagram of the electromagnetic parking mode in an embodiment of the present invention;

[0029] Figure 3 This is a mathematical model diagram of the omnidirectional translation mode in an embodiment of the present invention;

[0030] Figure 4This is a mathematical model diagram of the in-situ rotation mode in an embodiment of the present invention;

[0031] Figure 5 This is a mathematical model diagram of the four-wheel steering mode in an embodiment of the present invention;

[0032] Figure 6 This is a mathematical model diagram of the four-wheel steering mode in an embodiment of the present invention;

[0033] Figure 7 This is a diagram of the closed-loop control and extended six-cycle mathematical model in an embodiment of the present invention. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] The mathematical model of vehicle body motion established in this invention is as follows: Figure 1 As shown, the four wheel positions are A, B, C, and D, and the center of the front wheel axle is E. This point is used as the input point for the vehicle's motion parameters, including rad_e (angle value in rad) and ve (speed value in m / s). L1 and L2 are the front and rear wheelbases and the wheel spacing on both sides of the vehicle, respectively. The origin of the Cartesian coordinate system is located at the center O of the vehicle, and the instantaneous center of rotation P is set on the X-axis.

[0036] 1) Without any motion command issued, it defaults to electromagnetic parking mode, meaning the speed of all four drive motors is 0 r / min; the steering direction at points A and D is counterclockwise, and the steering direction at points B and C is clockwise, with all steering angles set to 0. Its movement pattern is as follows Figure 2 As shown;

[0037] 2) When entering omnidirectional translation mode, the deflection angle of all four steering motors is... The speed values ​​of the four drive motors are all converted from ve (m / s). (d is the diameter of the drive motor hub), its motion pattern is as follows: Figure 3 As shown;

[0038] 3) When entering the stationary rotation mode, such as Figure 4 As shown, the established mathematical model of motion reveals that... In this mode, points A, B, C, and D all move in circles with center O. Since their turning radii are all the same, their corresponding turning angles are also the same. Points A and D rotate clockwise, while points B and C rotate counterclockwise. The speed values ​​of the four drive motors remain the same, all calculated from ve. Points A and C are driven forward or backward, while points B and D are driven backward or forward, thus achieving overall clockwise or counterclockwise rotation in place.

[0039] 4) When entering four-wheel steering mode, the steering angle at point E is set as follows: a right turn is a positive value, and a left turn is a negative value. For example... Figure 5 As shown, the established mathematical model of motion shows that during a right turn, achievable achievable During the turn, all the particles on the robot simultaneously move in a circle with point P as the center. Therefore, the magnitude and direction of the angular velocity ω are the same. From the velocity value ve at point E, the length of PE, and the right-hand rule, the space vector of the angular velocity can be obtained. achievable Using a unit vector perpendicular to the plane of motion, we can obtain The linear velocity at point A is the wheel's velocity, and its direction is the required steering angle. Similarly, the direction vectors corresponding to points B, C, and D can be calculated. From this, the rotational speeds of the drive motors at points A, B, C, and D, and the deflection angles of the steering motors, can be determined. Points A and B rotate clockwise, and points C and D rotate counter-clockwise; the driving directions at all four points are consistent. During a left turn, as... Figure 6 As shown, achievable achievable During the turn, all the particles on the robot simultaneously move in a circle with point P as the center. Therefore, the magnitude and direction of the angular velocity ω are the same. From the velocity value ve at point E, the length of PE, and the right-hand rule, the space vector of the angular velocity can be obtained. achievable Using a unit vector perpendicular to the plane of motion, we can obtain The module length is the linear velocity at point A, i.e., the wheel's velocity, and the direction is the required steering angle. Similarly, the direction vectors corresponding to points B, C, and D can be obtained. Furthermore, the rotational speeds of the drive motors at points A, B, C, and D, and the deflection angles of the steering motors, can be calculated. Points A and B rotate counter-clockwise, while points C and D rotate clockwise, with all four points having the same driving direction. This mode enables all four wheels to participate in steering, significantly reducing the turning radius and greatly improving maneuverability and passability. Simultaneously, the rotational speeds of each drive motor are differentially matched, avoiding wheel drag caused by differences in the turning radii at each point.

[0040] 5) Compared to general open control methods, this motion control also employs a closed-loop control method. That is, while receiving motion parameter commands, it reads the velocity and steering angle values ​​at any point A, B, C, or D in real time and converts them into the motion parameters corresponding to the input parameter point E. For example... Figure 7 As shown, during the right turn, the turning angle at point A is known to be rad_a, and the speed is va. Based on the established mathematical model of motion, MP = MA * tanrad_a. achievable During the turning process, all the particles of the robot are moving in concentric circles, and therefore have the same angular velocity value. According to the theory of circular motion, v = ω * r (the linear velocity v, angular velocity ω, and radius r of a point in the circle), we can obtain... The above calculations enable the conversion of the angle and velocity values ​​read from a single point A into the actual angle and velocity values ​​of the input parameter point E. This closed-loop control method allows the upper-level control end to compare the sent parameters and response parameters in real time, which can greatly improve the accuracy and stability of motion control in autonomous driving scenarios.

[0041] 6) The control mode involved in this invention also has strong expansion capabilities, allowing for the addition of six-wheel drive to the existing four-wheel drive system; for example... Figure 7 As shown, since the instantaneous steering center point is set on the X-axis of the vehicle body, the two additional wheels can be installed at points M and N, the centers of the front and rear wheels on the left and right sides, respectively. This ensures that the velocity directions of the two newly added wheels are always perpendicular to the turning radii MP and NP, eliminating the need for steering during turns and requiring only speed difference matching. This addition of two steering-free motors reduces cost and operational complexity while significantly improving driving capability, further meeting the needs of applications with larger loads and more complex road conditions.

[0042] Those skilled in the art will understand that implementing all or part of the processes of the above embodiments can be accomplished by operating the relevant hardware through a computer program. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the above embodiments. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc.

[0043] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A motion control method for a low-speed delivery robot, characterized in that, Includes the following steps: A mathematical model of vehicle motion is constructed as follows: the four wheel positions are A, B, C, and D, and the center position of the front wheel axis is E, which is used as the input point for the vehicle motion parameters, including the angle value rad_e and the speed value ve; L1 and L2 are the front and rear wheelbases and the wheel spacing on both sides, respectively; the origin of the plane rectangular coordinate system is located at the center point O of the vehicle, and the instantaneous center of steering P is set on the X-axis; Without any movement command issued, it defaults to electromagnetic parking mode; When entering omnidirectional translation mode, the deflection angle of all four steering motors is rad_e, with a value range of: - ≤rad_e ≤ ; When entering the stationary rotation mode, points A, B, C, and D all move in circles with O as the center. Their turning radii are all the same, so the corresponding turning angles are also the same. When entering four-wheel steering mode, all the mass points on the robot simultaneously make circular motion around point P as the center during the turning process. Therefore, the magnitude and direction of the angular velocity ω are the same. Determine the direction vectors corresponding to points A, B, C, and D, and set the speed values ​​of the drive motors and the deflection angle values ​​of the steering motors at the four points A, B, C, and D. The four-wheel steering mode specifically includes a right turn process and a left turn process: During the right turn, rad_p = rad_e, 0 ≤ rad_e ≤ , can be obtained =( ); = - , can be obtained =( , During the turning process, all the particles on the robot simultaneously move in a circle with point P as the center. Therefore, the magnitude and direction of the angular velocity ω are the same. From the velocity value ve at point E, the length of PE, and the right-hand rule, the space vector of the angular velocity can be obtained. =(0,0,-( )), = - , can be obtained =( , Using a unit vector perpendicular to the plane of motion, we can obtain... The module length is the linear velocity of point A, which is the speed of the wheel, and the direction is the required steering angle. Similarly, the direction vectors corresponding to points B, C, and D can be obtained, and then the speed values ​​of the drive motors and the deflection angle values ​​of the steering motors at points A, B, C, and D can be obtained. Among them, the steering at points A and B is clockwise, and the steering at points C and D is counterclockwise. The driving directions of the four points are all the same. During the left turn, rad_p = rad_e, - ≤rad_e <0, therefore we can obtain =( ); = - , can be obtained =( , During the turning process, all the particles on the robot simultaneously move in a circle with point P as the center. Therefore, the magnitude and direction of the angular velocity ω are the same. From the velocity value ve at point E, the length of PE, and the right-hand rule, the space vector of the angular velocity can be obtained. =(0,0,( )), = - , can be obtained =( , Using a unit vector perpendicular to the plane of motion, we can obtain... The linear velocity at point A is the speed of the wheel, and the direction is the required steering angle. Similarly, the direction vectors corresponding to points B, C, and D can be obtained, and then the rotational speed of the drive motors and the deflection angle of the steering motors at points A, B, C, and D can be obtained. The steering at points A and B is counterclockwise, and the steering at points C and D is clockwise. The driving directions of the four points are all the same.

2. The motion control method for a low-speed delivery robot as described in claim 1, characterized in that, Without any movement command being issued, it defaults to entering electromagnetic parking mode, specifically as follows: In electromagnetic parking mode, the speed of all four drive motors is 0 r / min; the steering direction at points A and D is counterclockwise, and the steering direction at points B and C is clockwise, with all steering angles set to 0. .

3. A motion control method for a low-speed delivery robot as described in claim 1 or 2, characterized in that, When entering omnidirectional translation mode, the deflection angle of all four steering motors is rad_e, with a value range of: - ≤rad_e ≤ Specifically: The speed values ​​of all four drive motors are ve, in m / s, and the converted speed value is rpm. d is the diameter of the drive motor hub.

4. A motion control method for a low-speed delivery robot as described in any one of claims 1 to 3, characterized in that, When entering the stationary rotation mode, points A, B, C, and D all move in circles with center O, and their turning radii are all the same, so their corresponding turning angles are also the same. Specifically: The established mathematical model of motion shows that tan rad_ = In this mode, points A, B, C, and D all move in circles with center O. Since their turning radii are all the same, their corresponding turning angles are also the same. Points A and D rotate clockwise, while points B and C rotate counterclockwise. The speed values ​​of the four drive motors remain the same, all being the speed values ​​converted from ve. Points A and C are driven forward or backward, while points B and D are driven backward or forward, thus achieving overall clockwise or counterclockwise rotation in place.

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