Lunar rover wheel soil characteristic-oriented slip rate control method and system and electronic equipment

Abstract

The invention provides a slip rate control method and system for lunar rover wheel soil characteristics and electronic equipment, aiming at wheel soil dynamic differences caused by different earth-moon environments, a lunar rover slip rate characteristic curve shows that a lunar rover does not have a so-called'optimal slip rate 'fixed point, so that the longitudinal force of a tire reaches a peak value at the point, and the slip rate of the lunar rover reaches the optimal slip rate. The problem that a conventional ground optimal slip rate control method fails on the lunar surface is solved, a function about the tire load rate and the slip rate is introduced into a four-wheel torque distributor of the lunar rover to serve as a target optimization function, and four-wheel torque is distributed in a coordinated mode on the basis that the longitudinal driving requirement is met. According to the method, the special wheel soil dynamic characteristics of the lunar rover are considered, the tire force is controlled based on the slip rate and the tire load rate, the situation that the wheel slip rate is too large and the tire force is saturated is prevented, and the running dynamic property and safety of the lunar rover are effectively improved.

Description

Technical Field

[0001] The present invention relates to a slip ratio control method, system and electronic device for lunar wheel-soil characteristics, and belongs to the technical field of slip ratio control. Background Technique

[0002] In recent years, lunar exploration has always been a hot issue in the field of deep space exploration at home and abroad. As a carrier for lunar surface patrol and movement, the lunar rover is the key to the successful implementation of lunar exploration missions and must have the ability to drive safely and smoothly for a long time. The lunar rover is a typical distributed drive wheeled chassis. The four wheels can be independently driven by in-wheel motors. At the same time, both the front and rear wheels can adjust the steering angle through independent steering mechanisms. The actuators include 4 drive motors and 2 steering motors, which is a redundant drive system. However, the lunar surface environment is complex, and the lunar surface is covered with a layer of soft lunar soil. Under the action of low gravity, the wheels are extremely prone to slipping, which not only increases the energy consumption during movement, but more importantly, it will further cause wheel sinkage and tire force saturation, resulting in the vehicle being difficult to control and losing stability. Therefore, studying the slip ratio control of the lunar rover is of great significance for improving the vehicle's power performance and stability when the vehicle moves quickly over a large range.

[0003] At present, the mature slip ratio control on the ground mostly adopts the optimal slip ratio control method. According to the tire characteristic curve, it can be found that ground vehicles usually have a so-called "optimal slip ratio". After that, when the slip ratio continues to increase, the longitudinal force of the wheel begins to decrease, and the lateral force margin also drops sharply. Therefore, the ground usually controls the slip ratio to remain near the optimal slip ratio. However, different from the configuration mainly composed of ground rubber tires and hard road surfaces, the lunar rover uses metal tires, and the working environment is soft lunar soil. The wheel-soil dynamics on the lunar surface are quite different from those on the ground. The slip ratio characteristic curve of the lunar rover shows that there is no so-called "optimal slip ratio" for the lunar rover, which makes the longitudinal force of the tire reach the peak at this point, resulting in the failure of the conventional optimal slip ratio control method on the lunar surface. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art, and provide a slip ratio control method, system and electronic device for lunar wheel-soil characteristics. Based on the differences in ground-lunar wheel-soil dynamics caused by the special lunar surface environment, an optimization function for four-wheel distribution target is constructed by using the slip ratio and tire load ratio, and the output torque of each wheel is adjusted in real time according to the tire force state to ensure the driving stability and power performance of the lunar rover.

[0005] The technical solution of the present invention is:

[0006] The present invention discloses a slip ratio control method for lunar wheel-soil characteristics, including:

[0007] Calculate the slip ratio and tire load ratio based on the vehicle motion state information;

[0008] Calculate the expected driving torque of the whole vehicle based on the target vehicle speed;

[0009] Construct a target optimization function based on the expected torque of the whole vehicle, the four-wheel slip ratio, and the tire load ratio;

[0010] Obtain the longitudinal tire force according to the target optimization function.

[0011] Further, in the above method, the slip ratio is specifically:

[0012]

[0013] where s ij is the four-wheel slip ratio, and ij ∈ {fl, fr, rl, rr} represent the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; V x is the longitudinal vehicle speed, ω ij is the four-wheel speed, and R eff is the wheel radius.

[0014] Further, in the above method, the tire load ratio ε is specifically:

[0015]

[0016] ij ∈ {fl, fr, rl, rr}

[0017] where μ is the road surface adhesion coefficient, F zij is the tire vertical load, F xij is the longitudinal tire force, and {fl, fr, rl, rr} represent the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively.

[0018] Further, in the above method, the expected driving torque T des of the whole vehicle is specifically:

[0019]

[0020] where is the target vehicle speed, k p , k i , k d are the PID control parameters respectively, V x is the longitudinal vehicle speed, is the differential term of the longitudinal vehicle speed.

[0021] Further, in the above method, the target optimization function G is specifically:

[0022]

[0023] such that ∑F xij R eff = T des

[0024] where p k is the control weight of the tire load rate, k ∈ {1, 2, 3, 4} represents the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively, and it is a function of the slip ratio s ij ; μ is the road surface adhesion coefficient, F zij is the tire vertical load, F xij is the tire longitudinal force; fl, fr, rl, rr represent the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; R eff is the wheel radius; T des is the expected driving torque of the whole vehicle.

[0025] Furthermore, in the above method, the control weight of the tire load rate is specifically:

[0026]

[0027] where p k is the control weight of the tire load rate, k ∈ {1, 2, 3, 4} represents the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; K, a, b are adjustment parameters, e is the exponential function, s ij is the four-wheel slip ratio, ij ∈ {fl, fr, rl, rr} represents the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively.

[0028] The present invention discloses a slip rate control system for lunar wheel-soil characteristics, including:

[0029] An acquisition module that acquires vehicle motion state information and sends it to the calculation module;

[0030] A control module that calculates the slip rate and tire load rate based on the vehicle motion state information; calculates the expected driving torque of the whole vehicle based on the target vehicle speed; constructs a target optimization function based on the expected torque of the whole vehicle, four-wheel slip ratio, and tire load rate; and obtains the tire longitudinal force according to the target optimization function and sends it to the actuator;

[0031] An actuator that controls the vehicle according to the tire longitudinal force.

[0032] The present invention discloses an electronic device, including a memory and a processor:

[0033] The memory is used to store one or more computer instructions;

[0034] The processor is used to execute the one or more computer instructions for:

[0035] Calculate the slip ratio and tire load ratio based on the vehicle motion state information;

[0036] Calculate the expected driving torque of the whole vehicle based on the target vehicle speed;

[0037] Construct a target optimization function based on the expected torque of the whole vehicle, the four-wheel slip ratio, and the tire load ratio;

[0038] Obtain the longitudinal tire force according to the target optimization function.

[0039] The beneficial effects of the present invention compared with the prior art are as follows:

[0040] (1) The present invention provides a slip ratio control method for lunar wheel-soil characteristics, which fully considers the differences between the earth-moon environments and the dynamic changes of lunar wheel-soil caused by lunar rover metal tires, solves the problem of the failure of the ground optimal slip ratio on the lunar surface, realizes the slip ratio control under the large-range and fast movement of the lunar rover, prevents wheel slippage, and improves the power performance and stability of the vehicle.

[0041] (2) The present invention proposes a method for self-tuning the control weight based on the Logistic function, which realizes the adaptive adjustment of the control weight of the four-wheel load ratio according to the change of the slip ratio, effectively prevents the saturation of the lunar surface tire force, and has the advantages of strong operability, high control accuracy, and strong robustness.

[0042] (3) The method of the present invention considers the special wheel-soil dynamic characteristics of the lunar rover, controls the tire force based on the slip ratio and the tire load ratio, prevents the wheel slip ratio from being too large and the tire force from being saturated, and effectively improves the driving power performance and safety of the lunar rover.

[0043] (4) Aiming at the wheel-soil dynamic differences caused by different earth-moon environments, the slip ratio characteristic curve of the lunar rover shows that there is no so-called "optimal slip ratio" fixed point for the lunar rover, which makes the longitudinal tire force reach the peak at this point, resulting in the failure of the conventional ground optimal slip ratio control method on the lunar surface. A function related to the tire load ratio and the slip ratio is introduced as the target optimization function in the four-wheel torque distributor of the lunar rover to coordinately distribute the four-wheel torque on the basis of meeting the longitudinal driving demand. Description of the Drawings

[0044] Figure 1 It is a comparison diagram of the slip ratio control effect in a preferred embodiment of the present invention; (a) Controller on, (b) Controller off;

[0045] Figure 2 It is the p in the present invention k The parameter varies with the slip ratio s ij Schematic diagram of the curve;

[0046] Figure 3 This is the flow chart of the present invention. Detailed implementation manners

[0047] The present invention will be further described in detail below with reference to the accompanying drawings.

[0048] The lunar rover autonomously moves towards the destination at a preset target vehicle speed. The navigation system observes the vehicle state information in real time and outputs it to the controller. In the controller, the four-wheel slip ratio and the tire load ratio of each wheel are obtained through calculation. Combining with the target vehicle speed requirement, a target optimization function is constructed in the four-wheel torque distributor, and the control degree of the tire load ratio is adaptively adjusted according to the current wheel slip degree to prevent tire force saturation.

[0049] As Figure 3 shown, this embodiment provides a slip ratio control method for lunar wheel-soil characteristics, including the following steps:

[0050] Step 1: Observe and calculate the slip ratio and tire load ratio through vehicle motion state information.

[0051] Use the tire load ratio ε to describe the friction ellipse constraint of the tire longitudinal force and lateral force to prevent tire force saturation:

[0052]

[0053] where μ is the road surface adhesion coefficient, F zij is the tire vertical load, F xij is the tire longitudinal force, and ij ∈ {fl, fr, rl, rr} respectively represent the left front wheel, right front wheel, left rear wheel, and right rear wheel.

[0054] Based on the vehicle longitudinal vehicle speed provided by the navigation system and the wheel speeds of each wheel feedback by the drive system, calculate the four-wheel slip ratio s ij respectively as:

[0055]

[0056] where, V x is the vehicle longitudinal vehicle speed, ωij is the four-wheel wheel speed, ij ∈ {fl, fr, rl, rr} respectively represent the left front wheel, right front wheel, left rear wheel, and right rear wheel, and R eff is the wheel radius.

[0057] Step 2: Calculate the expected driving torque of the whole vehicle based on the target vehicle speed.

[0058] Obtain the expected driving torque T of the whole vehicle through PID control based on the deviation between the target vehicle speed and the current vehicle speed des .

[0059]

[0060] Among them, is the target vehicle speed, k p , k i , k d are the PID control parameters respectively, is the derivative of the vehicle's longitudinal vehicle speed.

[0061] Step 3: Construct a target optimization function based on the vehicle's expected torque, four-wheel slip ratio, and tire load ratio to achieve coordinated distribution of the four-wheel torque.

[0062] When designing the four-wheel torque distributor, fully consider the special slip ratio characteristics of the lunar rover, the coupling relationship between the tire load ratio and the wheel slip ratio. By reasonably distributing the four-wheel longitudinal forces, each tire can maintain a small slip ratio to improve the safety and power performance of the lunar rover. When the slip ratio is small, there is still a large control margin for the tire longitudinal force, and the tire load ratio is small. As the slip ratio increases, the tire longitudinal force rises slowly, the control margin decreases, and the tire load ratio gradually increases until the tire longitudinal force reaches saturation. By observing the wheel slip ratio and the tire load ratio, when the slip ratio and tire load ratio of a certain wheel are large, reduce the output torque of this wheel, reduce the wheel longitudinal force, avoid wheel spin and skidding, and prevent vehicle instability caused by tire force saturation.

[0063] Therefore, when performing four-wheel torque distribution, not only should the four-wheel torque meet the vehicle's expected driving requirements, but also the slip ratio and tire load ratio of the wheels should be restricted. The design target optimization function G is shown as follows.

[0064]

[0065] Among them, pk is the control weight of the four-wheel load ratio, which is a function of the slip ratio s ij . Based on the wheel-soil characteristics of the lunar rover, when the wheel slip degree is small, the tire load ratio is small, and at this time p k increases slowly with the slip ratio s ij . When the wheel slip ratio gradually increases, p k increases rapidly with the slip ratio s ij to quickly reduce the output torque of the skidding wheel and reduce the saturation degree of the tire force. When the wheel slip ratio gradually rises until the tire force reaches saturation, p k reaches the peak value and basically no longer changes subsequently. p k The specific design is shown as follows.

[0066]

[0067] Among them, e is the exponential function, K, a, and b are adjustment parameters, and both a and b are positive numbers. The schematic diagram of the change of p k is as shown in Figure 2as shown

[0068] By solving the target optimization function and coordinately distributing the longitudinal forces of the four wheels, wheel slip can be effectively suppressed, tire force saturation can be prevented, and the mobility performance of the lunar rover can be improved. Figure 1 The following figure is a comparison chart of the slip rate control effect in the preferred embodiment of the present invention. It can be seen that after the controller is turned on, the slip rates of the four wheels always remain within 0.4. Compared with the peak value of 1.2 of the slip rates of the four wheels when the controller is turned off, it is improved by about 0.8, and the control effect is remarkable.

[0069] This embodiment discloses a slip rate control system for lunar wheel-soil characteristics, including:

[0070] An acquisition module that acquires vehicle motion state information and sends it to the calculation module;

[0071] A control module that calculates the slip rate and tire load rate based on the vehicle motion state information; calculates the expected driving torque of the whole vehicle based on the target vehicle speed; constructs a target optimization function based on the expected torque of the whole vehicle, the slip rates of the four wheels, and the tire load rate; and obtains the longitudinal tire force according to the target optimization function and sends it to the actuator;

[0072] An actuator that controls the vehicle according to the longitudinal tire force.

[0073] This embodiment discloses an electronic device, including a memory and a processor:

[0074] The memory is used to store one or more computer instructions;

[0075] The processor is used to execute the one or more computer instructions for:

[0076] Calculating the slip rate and tire load rate according to the vehicle motion state information;

[0077] Calculating the expected driving torque of the whole vehicle based on the target vehicle speed;

[0078] Constructing a target optimization function based on the expected torque of the whole vehicle, the slip rates of the four wheels, and the tire load rate;

[0079] Obtaining the longitudinal tire force according to the target optimization function.

[0080] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be regarded as a limitation of the present invention. After those skilled in the art have read the above content, various modifications and substitutions to the present invention will be obvious. Therefore, the protection scope of the present invention should be defined by the appended claims.

[0081] The content not detailedly described in the specification of the present invention belongs to the well-known technology of those skilled in the art.

Claims

1. A slip rate control method for lunar wheel soil characteristics, characterized in that: include: Calculate the slip rate and tire load rate based on the vehicle motion status information; Based on the target vehicle speed, calculate the expected driving torque of the vehicle; Constructing the target optimization function based on the expected torque of the vehicle, the four-wheel slip rate and the tire load rate; According to the objective optimization function, the tire longitudinal force is obtained.

2. The method for controlling slip rate based on lunar wheel soil characteristics according to claim 1, characterized in that: The slip rate is specifically: Among them, s ij is the four-wheel slip rate, ij∈{fl,fr,rl,rr} represents the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; V x is the longitudinal speed of the vehicle, ω ij is the four-wheel speed, R eff is the wheel radius.

3. The method for controlling slip rate based on lunar wheel soil characteristics according to claim 1, characterized in that: The tire load factor ε is specifically: ij∈{fl,fr,rl,rr} Where μ is the road adhesion coefficient, F zij is the vertical load of the tire, F xij is the tire longitudinal force, and {fl, fr, rl, rr} represent the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively.

4. The method for controlling slip rate based on lunar wheel soil characteristics according to claim 1, characterized in that: The expected driving torque of the vehicle is T des , specifically: in, is the target speed, k p , k i , k d are PID control parameters, V x is the longitudinal speed of the vehicle, V x is the differential term of the vehicle's longitudinal velocity.

5. The method for controlling slip rate based on lunar wheel soil characteristics according to claim 4, characterized in that: The target optimization function G is specifically: Among them, p k is the control weight of the tire load rate, k∈{1,2,3,4} represents the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively, which is about the slip rate s ij function; μ is the road adhesion coefficient, F zij is the vertical load of the tire, F xij is the tire longitudinal force; fl, fr, rl, rr represent the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; R eff is the wheel radius; T des is the expected driving torque of the vehicle.

6. The method for controlling slip rate based on lunar wheel soil characteristics according to claim 5, characterized in that: The control weight of the tire load rate is specifically: Among them, p k is the control weight of the tire load rate, k∈{1,2,3,4} represents the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; K, a, b are adjustment parameters, e is an exponential function, s ij is the four-wheel slip rate, ij∈{fl,fr,rl,rr} represents the left front wheel, right front wheel, left rear wheel and right rear wheel respectively.

7. A slip rate control system for lunar wheel soil characteristics, characterized in that: include: The acquisition module collects the vehicle motion status information and sends it to the calculation module; The control module calculates the slip rate and tire load rate according to the vehicle motion state information; Based on the target vehicle speed, the expected driving torque of the vehicle is calculated; based on the expected torque of the vehicle, the four-wheel slip rate and the tire load rate, a target optimization function is constructed; based on the target optimization function, the tire longitudinal force is obtained and sent to the actuator; The actuator controls the vehicle based on the longitudinal force of the tire.

8. An electronic device, characterized in that: It includes a memory and a processor: the memory is used to store one or more computer instructions; The processor is configured to execute the one or more computer instructions to: Calculate the slip rate and tire load rate based on the vehicle motion status information; Based on the target vehicle speed, calculate the expected driving torque of the vehicle; Constructing the target optimization function based on the expected torque of the vehicle, the four-wheel slip rate and the tire load rate; According to the objective optimization function, the tire longitudinal force is obtained.

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