Power and saturation distribution strategy design method for omni-directional mobile chassis composed of robot Mecanum wheels and omni-directional wheels

Abstract

The invention discloses a power and saturation distribution strategy design method for an omni-directional mobile chassis composed of robot Mecanum wheels and omni-directional wheels, and the method comprises the following steps: S1, in an algorithm, considering and setting the earth gravity as G and the physical Alembert virtual force as (G / g) * a, the driving force is Fx (x is the number of the xth wheel) and Lx (x is the distance from the xth wheel to the gravity center); s2, the robot chassis is set to rotate around the gravity center when moving, and meanwhile, the robot chassis is also set to do translational motion; s3, setting an ideal contact point between each wheel and the ground, and considering the motion state of the chassis. And analyzing the rotating condition of each point around the gravity center, and calculating the dynamic vertical load of different wheels by utilizing the moment balance condition. And S4, through the dynamic vertical load, the driving force of the robot is reasonably distributed. And S5, if the chassis power is saturated, the driving force is distributed for the second time, the moving stability of the robot is guaranteed, and it is guaranteed that the robot moves according to instructions of an upper computer or an automatic driving algorithm. According to the designed scheme, the problems of chassis slipping and power saturation during running of the robot can be solved.

Description

Technical Field

[0001] The invention belongs to the technical field of performance optimization of an omnidirectional mobile robot chassis composed of a Mecanum wheel and an omnidirectional wheel, and in particular relates to a design method for a power and saturation distribution strategy of an omnidirectional mobile chassis composed of a Mecanum wheel and an omnidirectional wheel of a robot. Background Art

[0002] Mecanum wheels and omnidirectional wheels are widely used in the driving of omnidirectional mobile robots. Although the chassis of this wheel system can easily achieve the effect of front-to-back and left-to-right translation, the chassis performance is unsatisfactory in practice, especially at high speeds, it is easy to slip and deviate, affecting the robot's movement accuracy and acceleration. After analysis, it is believed that the root cause is that the torque distribution does not take into account the actual load, and there is also the problem of power saturation under extreme conditions. To this end, we propose a chassis power and distribution strategy design method under saturation to solve the above problems. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a design method for a power saturation distribution strategy of an omnidirectional mobile chassis composed of a Mecanum wheel and an omnidirectional wheel.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] A chassis power saturation distribution strategy design method comprises the following steps:

[0006] S1. Set gravity to G, D'Alembert's virtual force in physics to (G / g)*a, driving force to F_x (x is the number of the x-th wheel), L_x (x is the distance from the x-th wheel to the center of gravity); S2. Set the vehicle to rotate around the center of gravity and also to translate;

[0007] S3. Assume that the vehicle starts from the ideal contact point between each wheel and the ground, analyze the rotation of the above contact point around the center of gravity, and use the condition of moment balance to obtain the following formula:

[0008]

[0009] S4. According to the vertical load of each wheel, the driving force of the wheel is constrained, so that the chassis movement is more precise.

[0010] S5. If the ideal wheel driving force in S4 exceeds the output limit of the chassis motor, the chassis power is saturated, and the chassis power is redistributed through the proportional constraint algorithm.

[0011] Furthermore, in step S5, after the motor power is saturated, such as in the starting stage, the power should be redistributed to meet the motion command. According to the output of the PID, the power ratio is reconfigured. The specific method is to not limit the PID, take the motor with the highest PID output value as a reference, remap it to the maximum value of the motor drive, obtain the scaling ratio, and multiply the output of all motors by the ratio value.

[0012] Furthermore, in step S3, the algorithm is used to model the entire vehicle, obtain vehicle motion information from acceleration, and dynamically calculate wheel loads. The main assumption is that the wheels can move freely under 3D rotation conditions, and there is a force [x, y, z] at the axle. Consistent with the previous method, each wheel is used as a rotation point, gravity*distance+wheel force*distance=acceleration*mass, and a formula group is constructed.

[0013] Furthermore, using the formula group, four basic equations are listed, where F is the driving force vector of each wheel, which is an unknown quantity, L is the distance vector between wheels and between wheels and the center, Acc is the acceleration vector, M is the vehicle mass, which is a scalar, and G is the acceleration due to gravity:

[0014]

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The solution designed by the present invention can optimize the problems of skidding and power saturation of the driving chassis of an omnidirectional mobile robot composed of Mecanum wheels and omnidirectional wheels. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The SAE standard vehicle coordinate system diagram of the vehicle in the present invention;

[0018] Figure 2 It is a schematic diagram of the vehicle movement in the present invention;

[0019] Figure 3 It is the code formula diagram;

[0020] Figure 4 Define a graph for vehicle coordinates and wheel numbers. DETAILED DESCRIPTION

[0021] The following will describe the implementation methods of the present application in detail with the help of accompanying drawings and examples, so that the implementation process of how the present application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0022] A chassis power saturation distribution strategy design method is used to optimize the design of the four-wheel drive problem based on the SAE standard vehicle coordinate system. Due to the virtual center of gravity transfer during starting and turning, the load on each wheel will increase or decrease. Figure 1 As shown, G is gravity, (G / g)*a is the D'Alembert virtual force in physics, and the driving force is F. Since it is the starting stage, air resistance is ignored.

[0023] like Figure 2 As shown, the vehicle rotates around the center of gravity and also translates. Starting from the ideal contact point between each wheel and the ground, the rotation of the above contact point around the center of gravity is analyzed. Based on the conditions of torque balance, four basic equations can be listed, where F is the driving force vector of each wheel, which is an unknown quantity, L is the distance vector between wheels and between wheels and the center, Acc is the acceleration vector, M is the vehicle mass, which is a scalar, and G is the acceleration of gravity. The following formula can be obtained:

[0024]

[0025] When accelerating, the acceleration slows down due to the increased load on the rear wheel. This makes the PID more inclined to increase the output to the rear wheel, but the power of the 3508 motor is very easy to saturate, and it is almost running at the maximum torque, making the actual current (torque) output by the front and rear wheels consistent, both of which are the maximum current value of 16384, resulting in inconsistent acceleration and a speed difference between the front and rear wheels. Ultimately, it actively causes slippage. Conversely, if the acceleration is reduced, this problem can be better solved, but it cannot meet the acceleration requirements of the robot. The best solution should be to replace a more powerful motor.

[0026] After solving the above algorithm, the vertical load of each wheel is obtained, and the driving force of the wheel is constrained according to the load, so that the chassis movement is more accurate.

[0027] If the constrained driving force exceeds the maximum limit of the motor drive, the motor power is saturated. After the motor power is saturated, such as in the instantaneous starting stage, the power should be redistributed and the power ratio should be reconfigured according to the PID output. The specific method is to not limit the PID, take the motor with the highest PID output value as a reference, remap it to the maximum value of the motor output capacity, obtain the scaling ratio, and multiply the output of all motors by the proportional value, so that all PID outputs are within the range that the actuator can output. The overall algorithm flow is as follows: Figure 3 The vehicle coordinates and wheel numbers are defined as follows: Figure 4 shown.

[0028] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the present invention in any form. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention fall within the protection scope of the present invention.

[0029] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A design method for a power saturation distribution strategy for an omnidirectional mobile chassis composed of a robot Mecanum wheel and an omnidirectional wheel, characterized in that: The steps include: S1. Set gravity to G, D'Alembert's virtual force in physics to (G / g)*a, driving force to F_x (x is the number of the x-th wheel), L_x (x is the distance from the x-th wheel to the center of gravity); S2, setting the vehicle to rotate around the center of gravity and also to translate; S3. Assume that the vehicle starts from the ideal contact point between each wheel and the ground, analyze the rotation of the above contact point around the center of gravity, and use the condition of moment balance to obtain the following formula: S4. According to the vertical load of each wheel, the driving force of the wheel is constrained, so that the chassis movement is more precise. S5. If the ideal wheel driving force in S4 exceeds the output limit of the chassis motor, the chassis power is saturated, and the chassis power is redistributed through the proportional constraint algorithm.

2. The chassis power saturation distribution strategy design method according to claim 1 is characterized in that: In step S5, after the motor power is saturated, for example, in the starting stage, the power should be redistributed to meet the motion command, and the power ratio should be reconfigured according to the PID output. The specific method is to not limit the PID, take the motor with the highest PID output value as a reference, remap it to the maximum value of the motor drive, obtain the scaling ratio, and multiply the output of all motors by the ratio value.

3. The chassis power saturation distribution strategy design method according to claim 1 is characterized by: In step S3, a traction control system is used, that is, the whole vehicle is modeled, the vehicle motion information is obtained from the acceleration, and the wheel load is dynamically calculated. The main assumption is that the wheels can move freely under 3D rotation conditions, and there is a force [x, y, z] at the axle. Consistent with the above method, each wheel is used as a rotation point, gravity*distance+wheel force*distance=acceleration*mass, and a formula group is constructed.

4. The chassis power saturation distribution strategy design method according to claim 3 is characterized by: Using the code formula, four basic equations are listed, where F is the driving force vector of each wheel, which is an unknown quantity, L is the distance vector between wheels and between wheels and the center, Acc is the acceleration vector, M is the vehicle mass, which is a scalar, and G is the acceleration due to gravity:

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