A four-steering-wheel AGV steering wheel failure fault-tolerant control method

Abstract

The present invention relates to a four-steering wheel AGV steering wheel failure fault-tolerant control method, belonging to the field of AGV intelligent control. The method comprises: establishing a four-steering wheel AGV kinematic model based on a two-steering wheel AGV kinematic model and Ackerman steering theory; establishing a lateral dynamics model and a longitudinal dynamics model of the car; linearizing the four-steering wheel AGV car model; designing an optimization solution objective function of a prediction model according to a system model; designing a corresponding MPC trajectory tracking controller according to the system's constraints on the car's speed and angular velocity; establishing a trajectory tracking fault-tolerant control objective function based on a differential model when four steering wheels fail; and designing a differential drive controller according to the trajectory tracking fault-tolerant control objective function. The present invention can ensure the trajectory tracking control function of the car while improving the load-bearing performance of the four-steering wheel AGV; and solves the problem of possible loss of control or control failure of the car's steering wheel during control.

Description

Technical Field

[0001] The invention belongs to the field of AGV intelligent control and relates to a steering wheel failure fault-tolerant control method for a four-steering-wheel AGV. Background Art

[0002] An Automated Guided Vehicle (AGV) is an automated transport device that can travel along a predetermined path without the need for manual navigation. It generally uses batteries as a power source, and commonly used navigation methods include magnetic navigation, laser navigation, etc.

[0003] With the continuous improvement of the level of automated production in all walks of life, automated guided vehicles, as a highly automated means of transportation, have demonstrated the advantages of safety, speed, efficiency, and low cost, and have gradually become a core component of modern logistics systems, which has greatly promoted the development of logistics and industrial automation.

[0004] However, faced with complex logistics environments and increasingly stringent production requirements, traditional dual-steering wheel AGVs have been unable to meet the needs of flexibility and load capacity. Four-steering wheel AGVs have gradually entered the logistics industry with their greater load capacity and higher flexibility, but with this comes more complex trajectory tracking control and fault-tolerant control. As an overdrive system, each steering wheel of the four-steering wheel AGV can provide power and steering functions, and each motor is independently controllable, so it has high redundancy in terms of function, and has good fault tolerance when a wheel has a problem. Therefore, for the steering wheel failure fault-tolerant control of the four-steering wheel AGV, it is necessary to make full use of its multiple steering wheels. Summary of the invention

[0005] In view of this, an object of the present invention is to provide a steering wheel failure fault-tolerant control method for a four-steering-wheel AGV.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for controlling a steering wheel failure of a four-steering-wheel AGV, the method comprising the following steps:

[0008] S1: Establish the kinematic model of AGV based on the two-steering wheel AGV kinematic model and Ackerman steering theory;

[0009] S2: Establish the differential steering model of AGV;

[0010] S3: Design the objective function of model predictive control based on the aforementioned AGV system model;

[0011] S4: Combined with the objective function of the aforementioned model predictive control, the objective function of the four-steering-wheel AGV based on the differential model is designed;

[0012] S5: Design a differential drive controller for the AGV with steering wheel failure based on the aforementioned trajectory tracking fault-tolerant control objective function.

[0013] Optionally, S1 specifically includes: firstly using the relationship between the inner and outer wheel angles of the Ackerman principle, simplifying the four-steering wheel model into a double-steering wheel model for analysis, and performing operational modeling. The result of modeling the four-steering wheel AGV is:

[0014]

[0015]

[0016] Among them, V1~V4 and α1~α4 are the speeds and deflection angles of the four steering wheels respectively, ω is the turning angular velocity of the vehicle, and D1Q, D2Q, D3Q, and D4Q are the turning radii of the four steering wheels respectively.

[0017] Optionally, in S2, the AGV differential steering model established is:

[0018]

[0019] Among them, v1, v2, v3, and v4 represent the differential speeds of the four steering wheels respectively.

[0020] Optionally, in S3, the objective function of the model predictive control designed according to the system model is:

[0021] Y(t)=Ψ t ξ(t)+Θ t ΔU(k)

[0022] in:

[0023] Y(t)=[eta(t+1|t), eta(t+2|t),…, eta(t+N c |t),…,η(t+N p |t)] T Represents the output of the system;

[0024] It represents the state parameter of the system;

[0025] ΔU(k)=[Δu(t|t), Δu(t+1|t),…, Δu(+N c |t)] T represents a sequence of control increments;

[0026] Represents the control quantity parameter.

[0027] Optionally, in S4, the objective function of the vehicle based on the differential model in the fault-tolerant control of the four-steering-wheel AGV is obtained as follows:

[0028]

[0029] Among them, N p is the prediction time domain, N c To control the time domain, Q and R are weight matrices, ρ is the weight coefficient, and ε represents the relaxation factor.

[0030] Optionally, in S5, the differential drive controller model designed according to the trajectory tracking fault-tolerant control objective function is:

[0031]

[0032] Among them, v1 and v2 are the right wheel speed and left wheel speed of the AGV respectively; Δα is the instantaneous turning angle of the vehicle body; ΔD e is the speed deviation of the vehicle body after time Δt.

[0033] The beneficial effects of the present invention are:

[0034] (1) The present invention designs a trajectory tracking fault-tolerant control differential drive controller for a four-steering-wheel AGV when all steering wheels fail, thereby solving the problem of possible loss of control or control failure of the steering wheels of the vehicle during trajectory tracking control.

[0035] (2) The present invention provides a method for establishing a kinematic differential steering model of an AGV vehicle.

[0036] (3) The present invention provides a method for designing the objective function of the differential model of a four-steering wheel AGV vehicle in combination with model predictive control.

[0037] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0039] Figure 1 This is a schematic diagram of the kinematic model of the AGV vehicle;

[0040] Figure 2 This is a schematic diagram of the differential steering model of the car;

[0041] Figure 3 Flowchart of the trajectory tracking differential drive controller. DETAILED DESCRIPTION

[0042] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0043] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0044] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0045] See also Figure 1 to Figure 3 The embodiment of the present invention provides a steering wheel failure fault-tolerant control method for a four-steering-wheel AGV, and the specific steps are as follows:

[0046] 1) First, simplify the four-steering wheel model into a dual-steering wheel model, and use the Ackerman principle to understand the relationship between the inner and outer wheel angles, so that the motion can be solved when the AGV moves, and the deflection angle, speed and turning radius of each wheel can be calculated.

[0047] Figure 1In the equation, O is the instantaneous center of velocity; Q is the center of the vehicle; A is the rotation center of the virtual front steering wheel; B is the foot of the perpendicular line through the instantaneous center of velocity O to AC; C is the rotation center of the virtual rear steering wheel. Assume that the clockwise rotation angle of the steering wheel is positive and the counterclockwise rotation angle is negative. The instantaneous center of velocity of the instantaneous AGV is calculated by the angles θ1 and θ2 of the virtual steering wheel rotation.

[0048] The instantaneous center position of velocity can be obtained through trigonometric functions of structural dimensions and rigid body constraints:

[0049]

[0050]

[0051] AC=AB+BC

[0052] Where: θ1, θ2 are the outputs calculated by the algorithm.

[0053] According to the obtained θ1 and θ2, we can calculate:

[0054]

[0055] BC=AC-AB

[0056]

[0057]

[0058] From this, the turning radius OQ can be obtained as:

[0059]

[0060] According to the currently set speed V and the calculated turning radius OQ, the current turning angular velocity of the vehicle can be obtained as:

[0061]

[0062] According to the Ackerman principle, the turning centers of all steering wheels and the turning centers of the center of mass intersect at point Q. After the turning radius is known, the coordinates of O are known as (O x , O y ), according to the center of mass of the car as the origin, the coordinates of the four steering wheels are also known, and the lengths of the turning radii D1Q, D2Q, D3Q, and D4Q of the four small wheels can be calculated respectively according to the four-wheel AGV car.

[0063] According to the known angular velocity ω, the speeds V1~V4 of the four steering wheels and the deflection angles α1~α4 of the four steering wheels can be obtained respectively:

[0064]

[0065]

[0066] 2) Establish the differential steering model of the AGV, such as Figure 2 shown.

[0067] According to the model established in 2, the kinematic equation of the car can be obtained as follows:

[0068]

[0069] From the above formula, we can see that in the global coordinate system, the posture (x, y, θ) of the four-wheel drive AGV depends on the speed of each driving wheel (v1, v2, v3, v4). In addition, the rigidity constraint v=v o1 cos|α|=v o2 cos|β|, where v o1 , v o2 is the center point velocity of the front and rear drive units. When moving in a straight line, the angles α and β between the front and rear drive units and the vehicle body are both 0, and the motion control formula can be obtained as follows:

[0070] v1=v2=v3=v4=v o1 =v o2 =v

[0071] When the car moves in an arc, according to the kinematic model established above, the turning radius of the car can be obtained as

[0072]

[0073] Where d is half of the vehicle length, we can get When the car turns, there are three situations. The speeds of the front and rear cars in each section are not necessarily the same, which are: In the first stage of the circular turn, the center of mass speed of the front drive unit v is known. o1 =v, the turning radius is R, then:

[0074]

[0075] The center of mass velocity v of the drive unit is known in the second stage of the circular turn o1 =v o2 , α=β.

[0076] The velocity v of the center of mass of the rear drive unit is known in the third stage of the circular turn. o2 =v, the turning radius is R, then

[0077]

[0078] 3) Design the objective function of model predictive control based on the system model, which will facilitate the subsequent design of the objective function of the four-steering wheel AGV based on the differential model.

[0079] When the state quantity of a certain working point of the nonlinear system is ξ0 and the output quantity is u0, a control input quantity is given within the prediction time domain. Then its system state quantity is According to the description of nonlinear system, it can be expressed as:

[0080]

[0081] By performing Taylor series expansion on the above equation with only the first-order term retained, we can obtain the linear time-varying system equation after the linearization of the nonlinear discrete system:

[0082]

[0083] The linear time-varying system model that can be derived from the above linear time-varying system equation is:

[0084]

[0085] Then change the linearized system equations into incremental form, through The above formula can be transformed into:

[0086]

[0087] The matrix in the above formula They are [C k，t 0], m and n represent the dimension of the control quantity and the dimension of the state quantity respectively.

[0088] In addition, it is assumed here that: A k，t =A t，t , k = 1, ..., t + N - 1; B k，t =B t，t , k=1,…,t+N-1.

[0089] The system prediction output in the prediction time domain (i.e., the objective function of model predictive control) can be obtained:

[0090] Y(t)=Ψ t ξ(t)+Θ t ΔU(k)

[0091] in:

[0092] Y(t)=[eta(t+1|t), eta(t+2|t),…, eta(t+N c |t),…,η(t+N p |t)] T Represents the output of the system;

[0093] It represents the state parameter of the system;

[0094] ΔU(k)=[Δu(t|t), Δu(t+1|t),…, Δu(t+N c |t)] T represents a sequence of control increments;

[0095] Represents the control quantity parameter.

[0096] 4) According to the above formula, combined with the design of the model predictive control objective function, the objective function design of the four-steering wheel AGV based on the differential model is obtained as follows:

[0097]

[0098] Among them, N p is the prediction time domain, N c To control the time domain, Q and R are weight matrices, ρ is the weight coefficient, and ε represents the relaxation factor.

[0099] 5) Redesign the differential drive controller of the car, and its control flow chart is as follows Figure 3 The steering calculation method obtained by the differential of the steering wheel of the AGV is:

[0100] When the right wheel speed is v1 and the left wheel speed is v2, the instantaneous turning angle of the vehicle is

[0101]

[0102] Vehicle speed v along the y axis o1 After a period of time Δt, a deviation ΔD will be generated. e :

[0103] ΔD e =v o1 sinα1·Δt

[0104] When α1 is very small, sinα1 can be approximately regarded as α1, then

[0105] ΔD e =v o1 α1·Δt

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A four-steering-wheel AGV steering wheel failure fault-tolerant control method, characterized in that: The method comprises the following steps: S1: Establish the kinematic model of AGV based on the two-steering wheel AGV kinematic model and Ackerman steering theory; S2: Establish the differential steering model of AGV; S3: Design the objective function of model predictive control based on the AGV system model; S4: Combined with the objective function of the aforementioned model predictive control, the objective function of the four-steering-wheel AGV based on the differential model is designed; S5: Design a differential drive controller for the AGV with steering wheel failure based on the objective function of the aforementioned four-steering-wheel AGV based on the differential model; Specifically, S1 is as follows: first, using the relationship between the inner and outer wheel angles of the Ackerman principle, the four-steering wheel model is simplified into a double-steering wheel model for analysis, and operational modeling is performed. The result of the four-steering wheel AGV modeling is: Where V1~V4 and α1~α4 are the speeds and deflection angles of the four steering wheels respectively, ω is the turning angular velocity of the vehicle, and D1Q, D2Q, D3Q, and D4Q are the turning radii of the four steering wheels respectively; In S2, the established AGV differential steering model is: Among them, v1, v2, v3, and v4 represent the differential speeds of the four steering wheels respectively; In S3, the objective function of the model predictive control is designed based on the system model: Y(t)=Ψ t ξ(t)+Θ t ΔU(k) in: Y(t)=[n(t+1|t),n(t+2|t),…,n(t+N) c |t),…,η(t+N p |t)] T Represents the output of the system; It represents the state parameter of the system; ΔU(k)=[Δu(t|t), Δu(t+1|t),…, Δu(t+N c |t)] T represents a sequence of control increments; Represents the control quantity parameter; In S4, the objective function of the small vehicle based on the differential model in the fault-tolerant control of the four-steering wheel AGV is obtained as follows: Among them, N p is the prediction time domain, N c To control the time domain, Q and R are weight matrices, ρ is the weight coefficient, and ε represents the relaxation factor; In S5, the differential drive controller model designed according to the trajectory tracking fault-tolerant control objective function is: Among them, v1 and v2 are the right wheel speed and left wheel speed of the AGV respectively; Δα is the instantaneous turning angle of the vehicle body; ΔD e is the speed deviation of the vehicle body after time Δt.

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