A motion control method and system for variable wheelbase speed difference steering of wheel-legged vehicle

Abstract

The present invention discloses a motion control method and system for variable wheelbase speed difference steering of a wheel-leg type vehicle, and relates to the field of robot technology. The method comprises: obtaining the expected longitudinal speed and the expected yaw angular velocity; determining the expected motion trajectory of the wheel center according to the path planning of the target wheel-leg type vehicle; solving the expected joint angle of the joint of the target wheel-leg type vehicle; constructing the dynamic model of the target wheel-leg type vehicle; obtaining the expected additional yaw moment according to the dynamic model and the expected yaw angular velocity; obtaining the total driving force according to the expected longitudinal speed and the actual longitudinal speed; calculating the expected driving torque of the joint according to the expected joint angle and the actual joint angle; calculating the expected driving torque of the wheel according to the total driving force and the expected additional yaw moment; determining the optimal solution from the expected driving torque of the wheel, and obtaining the expected motor torque of the wheel. The present invention can improve the steering efficiency of the wheel-leg type vehicle.

Description

Technical Field

[0001] The present invention relates to the field of robot technology, and in particular to a motion control method and system for a wheel-leg type vehicle with variable wheelbase and speed difference steering. Background Art

[0002] Wheel-legged vehicles cannot use traditional Ackerman steering due to space layout and volume limitations. However, speed differential steering has the advantages of simple structure, easy maintenance, strong maneuverability, and the ability to achieve on-the-spot steering. It is widely used in small wheeled vehicles and robot platforms. Wheel-legged vehicles have high requirements for the torque output performance of the motor during speed differential steering. Improving the steering performance of wheel-legged vehicles and reducing the burden on the motor have become hot issues. At present, research mainly focuses on changes in movement forms, such as improving the steering performance of wheel-legged vehicles through active roll, and improving the steering performance of wheel-legged vehicles through wheel-step compound driving. However, there are few studies based on changing the vehicle's dynamic characteristics to improve steering performance. Summary of the invention

[0003] The object of the present invention is to provide a motion control method and system for variable wheelbase speed difference steering of a wheel-leg type vehicle, which can improve the steering efficiency of the wheel-leg type vehicle and reduce the peak torque demand for the motor.

[0004] To achieve the above object, the present invention provides the following solution: a motion control method for a wheel-leg type vehicle with variable wheelbase and speed difference steering, the method comprising:

[0005] Obtaining a desired longitudinal velocity and a desired yaw angular velocity;

[0006] According to the path planning of the target wheel-legged vehicle, the expected motion trajectory of the wheel center is determined;

[0007] Calculating the expected joint angles of the joints of the target wheel-legged vehicle according to the expected motion trajectory of the wheel center; the joints include hip joints and knee joints;

[0008] Constructing a dynamic model of the target wheel-legged vehicle;

[0009] According to the dynamic model of the target wheel-legged vehicle and the desired yaw angular velocity, the sliding mode control theory is applied to obtain the desired additional yaw moment;

[0010] Obtaining the actual longitudinal speed and actual joint angle of the target wheel-legged vehicle;

[0011] According to the desired longitudinal speed and the actual longitudinal speed, a PID control theory is applied to obtain a total driving force;

[0012] According to the desired joint rotation angle and the actual joint angle, the desired driving torque of the joint is calculated by applying PD control theory;

[0013] Calculating a desired driving torque of the wheel according to the total driving force and the desired additional yaw moment;

[0014] Taking minimizing the error as the first optimization objective function and minimizing the sum of the wheel adhesion utilization as the second optimization objective function, the optimal solution is determined from the expected driving torque of the wheel, the expected motor torque of the wheel is obtained, and the motor corresponding to the target wheel-legged vehicle is controlled according to the expected driving torque of the joint and the expected motor torque.

[0015] Optionally, according to the path planning of the target wheel-legged vehicle, determining the expected motion trajectory of the wheel center specifically includes:

[0016] Constructing a first hip joint coordinate system; the first hip joint coordinate system takes the contact position between the target wheel-legged vehicle and the leg as the origin, the contact surface between the target wheel-legged vehicle and the leg as the horizontal plane, the direction perpendicular to the horizontal plane as the vertical direction of the wheel, and the moving direction of the target wheel-legged vehicle as the longitudinal direction of the wheel;

[0017] Calculating the position coordinates of the wheel center in the first hip joint coordinate system according to the positional relationship between the hip joint, the knee joint and the wheel;

[0018] According to the path planning of the target wheel-legged vehicle, the coordinates of the initial position and the coordinates of the target position are determined;

[0019] According to the expected longitudinal speed and the position coordinates, and the speed of the initial position and the target position is zero, a cubic polynomial interpolation function is applied to obtain the expected motion trajectory of the wheel center.

[0020] Optionally, the target wheel-legged vehicle includes front wheels and rear wheels;

[0021] The desired joint angle of the hip joint of the front wheel is:

[0022] ;

[0023] The desired joint angle of the knee joint of the front wheel is:

[0024] ;

[0025] The desired joint angle of the hip joint of the rear wheel is:

[0026] ;

[0027] The desired joint angle of the knee joint of the rear wheel is:

[0028] ;

[0029] in, is the desired joint angle of the hip joint of the front wheel; is the desired joint angle of the knee joint of the front wheel; is the desired joint angle of the hip joint of the rear wheel; is the desired joint angle of the knee joint of the rear wheel; The thigh length of the target wheel-legged vehicle, is the lower leg length of the target wheel-legged vehicle; ( , ) is the position coordinate of the wheel center of the target wheel-legged vehicle; is the joint rotation angle of the hip joint of the target wheel-legged vehicle; is the joint rotation angle of the knee joint of the target wheel-legged vehicle.

[0030] Optionally, the dynamic model of the target wheel-legged vehicle includes a longitudinal dynamic equation of the wheel-legged vehicle, a lateral dynamic equation of the wheel-legged vehicle, and a yaw dynamic equation of the wheel-legged vehicle;

[0031] The longitudinal dynamic equation of the wheel-legged vehicle is:

[0032] ;

[0033] The lateral dynamic equation of the wheel-legged vehicle is:

[0034] ;

[0035] The yaw dynamics equation of a wheel-legged vehicle is:

[0036] ;

[0037] in, Indicates that the left and right wheels are used , represent, Indicates the front and rear wheels are used , represent, represents the longitudinal velocity, represents the lateral velocity, represents the yaw angular velocity, represents the yaw moment of inertia of the wheel-legged vehicle, Indicates the lateral distance from the wheel center to the center of mass; The tires of wheel-legged vehicles are subjected to lateral forces during the steering process; The tires of wheel-legged vehicles are subjected to longitudinal forces during the steering process; The longitudinal force on the left front wheel; The longitudinal force on the right front wheel; The longitudinal force of the left rear wheel; The longitudinal force on the right rear wheel; m is the mass of the wheel-legged vehicle; is the longitudinal acceleration; for resistance; is the distance from the left front wheel to the center of mass; The left front wheel is subjected to lateral force; is the distance from the right front wheel to the center of mass; The right front wheel is subjected to lateral force; is the distance from the left rear wheel to the center of mass; The left rear wheel is subjected to lateral force; is the distance from the right rear wheel to the center of mass; The right rear wheel is subjected to lateral force; is the lateral acceleration; is the yaw angular acceleration.

[0038] Optionally, the expected additional yaw moment is:

[0039] ;

[0040] Where, M is the expected additional yaw moment; represents the yaw moment of inertia of the wheel-legged vehicle; is the desired yaw rate; is the expected yaw angular acceleration; Yaw angular velocity; is the weight factor; is the distance from the left front wheel to the center of mass; The left front wheel is subjected to lateral force; is the distance from the right front wheel to the center of mass; The right front wheel is subjected to lateral force; is the distance from the left rear wheel to the center of mass; The left rear wheel is subjected to lateral force; is the distance from the right rear wheel to the center of mass; The right rear wheel is subjected to lateral force; is the sliding mode approach rate calculated based on the tire model.

[0041] Optionally, the first optimization objective function is:

[0042] ;

[0043] ;

[0044] ;

[0045] ;

[0046] in, Control allocation error for desired longitudinal force and yaw moment distribution to wheel motors; is the coefficient matrix, is the lateral distance from the wheel center to the center of mass; is the tire longitudinal force matrix; is a 2-dimensional vector; is the weight factor; Expected vertical force; is the expected additional yaw moment; The longitudinal force on the left front wheel; The longitudinal force on the right front wheel; The longitudinal force of the left rear wheel; The right rear wheel is subjected to longitudinal force.

[0047] Optionally, the second optimization objective function is:

[0048] ;

[0049] in, is the sum of tire adhesion utilization; The tires of wheel-legged vehicles are subjected to longitudinal forces during the steering process; is the vertical force on the tire of the wheel-legged vehicle during the steering process; c is the optimization target weight factor; is the road adhesion coefficient.

[0050] A computer device comprises: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement any of the above-mentioned motion control methods for variable wheelbase speed difference steering of a wheel-legged vehicle.

[0051] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements any of the above-mentioned motion control methods for variable wheelbase speed difference steering of a wheel-legged vehicle.

[0052] A computer program product comprises a computer program, which, when executed by a processor, implements any of the above-mentioned motion control methods for variable wheelbase speed difference steering of a wheel-leg type vehicle.

[0053] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0054] In view of the defects of the prior art, the present invention proposes a variable wheelbase wheel center planning method and a hierarchical control strategy. The upper controller dynamically controls the yaw rate and longitudinal vehicle speed through the longitudinal resultant force and the yaw moment, and kinematically controls the hip and knee joint angles according to the reverse solution values. The lower controller optimizes the distribution of motor output. The control framework improves the steering efficiency of wheel-legged vehicles and reduces the peak torque demand for motors. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0056] Figure 1 A flow chart of the application of the control method for variable wheelbase speed difference steering of the wheel-leg type vehicle provided by the present invention.

[0057] Figure 2 This is a schematic diagram of the leg kinematics model of the wheel-legged vehicle provided by the present invention.

[0058] Figure 3 This is a schematic diagram of the inverse kinematics analysis of the front legs of the wheel-legged vehicle provided by the present invention.

[0059] Figure 4 This is a schematic diagram of the dynamics analysis of the wheel-legged vehicle provided by the present invention.

[0060] Figure 5 This is a schematic diagram of the tire force provided by the present invention.

[0061] Figure 6 A schematic diagram of an implementation framework of a control method for variable wheelbase speed difference steering of a wheel-legged vehicle provided by the present invention.

[0062] Figure 7 A schematic diagram of the structural framework of a control system for variable wheelbase speed difference steering of a wheel-legged vehicle provided by the present invention.

[0063] Figure 8 It is a schematic diagram of the control method effect of variable wheelbase speed difference steering of wheel-leg type vehicle.

[0064] Fig. 9 A schematic flow chart of the motion control method for variable wheelbase speed difference steering of a wheel-legged vehicle provided by the present invention.

[0065] Fig.10 This is a diagram of the internal structure of a computer device. DETAILED DESCRIPTION

[0066] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0067] The purpose of the present invention is to provide a motion control method and system for variable wheelbase speed difference steering of a wheel-legged vehicle, aiming to improve the steering efficiency of the wheel-legged vehicle and reduce the peak torque demand for the motor.

[0068] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0069] Example 1: Figures 1 to 9 As shown, the motion control method for variable wheelbase speed difference steering of a wheel-leg type vehicle in this embodiment includes steps S1 to S10.

[0070] Step S1: Obtain the desired longitudinal velocity and the desired yaw angular velocity.

[0071] In practical applications, a three-dimensional map is established through perception and path planning is performed to obtain the desired yaw angular velocity. .

[0072] Step S2: Determine the expected motion trajectory of the wheel center according to the path planning of the target wheel-legged vehicle.

[0073] S2 specifically includes steps S21 to S24.

[0074] Step S21: construct a first hip joint coordinate system. The first hip joint coordinate system takes the contact position between the target wheel-legged vehicle and the leg as the origin, the contact surface between the target wheel-legged vehicle and the leg as the horizontal plane, the direction perpendicular to the horizontal plane as the vertical direction of the wheel, and the moving direction of the target wheel-legged vehicle as the longitudinal direction of the wheel.

[0075] Step S22: Calculate the position coordinates of the wheel center in the first hip joint coordinate system according to the positional relationship between the hip joint, the knee joint and the wheel.

[0076] Step S23: Determine the coordinates of the initial position and the coordinates of the target position according to the path planning of the target wheel-legged vehicle.

[0077] Step S24: According to the expected longitudinal speed and the position coordinates, and the speeds of the initial position and the target position are zero, a cubic polynomial interpolation function is applied to obtain the expected motion trajectory of the wheel center.

[0078] In practical applications, when a wheel-legged vehicle is performing variable wheelbase speed differential steering, in order to maintain the stability of the changing process, it is necessary to perform motion planning on the trajectory of the wheel center. First, it is necessary to establish a leg kinematic model and a hip joint coordinate system, and then plan the motion trajectory of the wheel center under the hip joint coordinate system.

[0079] like Figure 2 As shown in the figure, a leg kinematic model is established in the hip joint coordinate system. The entire model has three degrees of freedom: hip joint, knee joint, and driving wheel. , are the angles of the hip and knee joints, , is the length of the thigh and calf. According to the position relationship in the figure, the coordinate position of the wheel center in the hip joint coordinate system can be solved:

[0080] .

[0081] .

[0082] in, is the longitudinal position of the wheel, is the vertical position of the wheel.

[0083] The wheel center trajectory planning is to plan the target position and speed. Using the cubic polynomial interpolation function for trajectory planning requires determining the initial position coordinates and the target position coordinates, and giving the constraint that the speed is zero at the initial and final moments to ensure the continuity of the wheel center speed. The cubic polynomial curve can be uniquely determined based on the above constraints: .

[0084] in, is the unknown coefficient for wheel center trajectory planning, include , , and , t is the time.

[0085] Constraint adjustments include: .

[0086] in, For the wheel center The initial position in direction, For the wheel center The target position in the direction, for The derivative of . is the longitudinal position of the wheel at t=0. For t=t d The longitudinal position of the wheel. is the wheel speed at t=0. For t=t d Wheel speed. is the duration of the wheelbase change process.

[0087] Substituting the constraints into the cubic polynomial, we can get the wheel center velocity expression: .

[0088] Among them, inverse kinematics requires the position of the wheel center relative to the hip joint coordinate system, so the wheel center coordinates are: .

[0089] in, For the wheel center The target position in the direction. The starting time for variable wheelbase. is the initial position of the wheel center relative to the hip joint coordinate system.

[0090] During the wheelbase change process, the posture needs to be kept stable so that the tires maintain good contact with the ground. The vertical wheel center position remains unchanged and the vertical speed remains at 0.

[0091] .in, for The derivative of . is the expected longitudinal velocity. is the expected longitudinal displacement.

[0092] Step S3: Calculate the expected joint angles of the joints of the target wheel-legged vehicle according to the expected motion trajectory of the wheel center. The joints include hip joints and knee joints.

[0093] In practical applications, the inverse kinematics model can solve the joint angle when the end position is known. In variable wheelbase speed differential steering, the end position is actuated according to the planned wheel center position, so the end position is a known quantity.

[0094] like Figure 3 As shown, three sets of coordinate systems are established is the coordinate system of the hip joint that rotates with the thigh, is the knee joint coordinate system that rotates with the calf, The wheel coordinate system rotates with the wheel. The front side of the wheel-legged vehicle adopts an "elbow" arrangement. According to the geometric relationship, the hip joint can be obtained. , knee rotation Wheel center position , The relationship is:

[0095] .

[0096] .

[0097] The rear side adopts the "knee-style" layout. Similarly, the rear leg hip joint turns and hind knee rotation Wheel center position , The relationship is:

[0098] .

[0099] .

[0100] in, is the desired joint rotation of the hip joint of the front wheel. is the desired joint angle of the knee joint of the front wheel. is the desired joint rotation of the hip joint of the rear wheel. is the desired joint angle of the knee joint of the rear wheel, with the superscript Indicates the front side, superscript Indicates the rear side, The thigh length of the target wheel-legged vehicle, is the lower leg length of the target wheel-legged vehicle. , ) is the position coordinate of the wheel center of the target wheel-legged vehicle. is the joint rotation angle of the hip joint of the target wheel-legged vehicle. is the joint rotation angle of the knee joint of the target wheel-legged vehicle.

[0101] Step S4: constructing a dynamic model of the target wheel-legged vehicle.

[0102] In practical applications, the yaw rate control strategy obtains different longitudinal driving forces on both sides of the vehicle based on the dynamic model. and lateral force , It represents the longitudinal distance from the center of mass to the tire wheel, and establishes the dynamic equations in the longitudinal, lateral and yaw directions.

[0103] The longitudinal dynamic equation of wheel-legged vehicle: .

[0104] Lateral dynamic equations of wheel-legged vehicles: .

[0105] The yaw dynamics equation of a wheel-legged vehicle: .

[0106] in, represents the longitudinal velocity, represents the lateral velocity, represents the yaw angular velocity, represents the yaw moment of inertia of the wheel-legged vehicle, Indicates the lateral distance from the wheel center to the center of mass. The tires of wheel-legged vehicles are subjected to lateral forces during the turning process. During the turning process of wheel-legged vehicles, the tires are subjected to longitudinal force. The left front wheel is subjected to longitudinal force. The longitudinal force on the right front wheel. The left rear wheel is subjected to longitudinal force. The right rear wheel is subjected to longitudinal force. m is the mass of the wheel-legged vehicle. is the longitudinal acceleration. For resistance. is the distance from the left front wheel to the center of mass. The left front wheel is subjected to lateral force. is the distance from the right front wheel to the center of mass. The right front wheel is subjected to lateral force. is the distance from the left rear wheel to the center of mass. The left rear wheel is subjected to lateral force. is the distance from the right rear wheel to the center of mass. The right rear wheel is subjected to lateral force. is the lateral acceleration. is the yaw angular acceleration.

[0107] Without considering the vertical movement of the wheel, only the plane movement and rotation of the vehicle are considered, and the wheel force analysis is obtained as follows: Figure 5 As shown, the wheel torque balance equation is established: .

[0108] in, is the moment of inertia of the tire, is the rotation speed of each tire, is the tire driving torque, is the resistance torque of the tire, is the tire radius. is the acceleration of each tire. Figure 5 In, T fij The resistance moment ij is the same as above, indicating left, right, front and back, F zij Indicates the vertical support force, F xij Represents the longitudinal driving force.

[0109] When generating the desired driving torque of the wheel, the wheel torque balance equation must be satisfied.

[0110] The tire model is a carrier that reflects the relationship between the wheel-legged vehicle and the ground. During driving, the tire will be subjected to longitudinal force, lateral force, etc., and is related to the driving state of the wheel-legged vehicle. The Dugoff tire model responds better to the nonlinear characteristics of the tire, so the Dugoff tire model is selected.

[0111] Because the variable wheelbase speed differential steering will have a process of changing wheelbase, it will generate additional speed , so the calculation formula for each tire side slip angle is: .

[0112] in, is the left front wheel slip angle. is the right front wheel slip angle. is the left rear wheel slip angle. is the right rear wheel slip angle. It is the speed of the wheel center relative to the fuselage during the wheelbase change of the left front wheel. It is the speed of the wheel center relative to the fuselage during the wheelbase change of the right front wheel. It is the speed of the wheel center relative to the fuselage during the wheelbase change of the left rear wheel. It is the speed of the wheel center relative to the fuselage during the wheelbase change of the right rear wheel.

[0113] During the speed differential steering process, the movement of the wheels consists of rolling and sliding. During the wheelbase change process, the additional sliding speed generated will affect the slip rate, and the speed directions of the front and rear wheels are opposite. The slip rate calculation formula is: .

[0114] in, is the left front wheel slip rate. is the right front wheel slip rate. is the left rear wheel slip rate. Right rear wheel slip rate. is the left front wheel speed. is the right front wheel speed. is the left rear wheel speed. is the right rear wheel speed.

[0115] During the movement of wheel-legged vehicles, there will be changes in state such as acceleration, deceleration, and steering, which will generate acceleration. The vertical force on each tire will also change, so the vertical force of the wheel is calculated as: .

[0116] in, is the center of mass height of the wheel-legged vehicle. is the vertical force on the left front wheel. is the vertical force on the right front wheel. is the vertical force on the left rear wheel. is the vertical force on the right rear wheel. is the mass of the wheel-legged vehicle. is the acceleration due to gravity. is the longitudinal acceleration. is the lateral acceleration.

[0117] Step S5: According to the dynamic model of the target wheel-legged vehicle and the desired yaw angular velocity, the sliding mode control theory is applied to obtain the desired additional yaw moment.

[0118] In practical applications, changes in wheelbase will directly affect the size of the lateral force, thereby changing the torque generated by the lateral force on the center of mass, making yaw rate control more difficult. In order to stably track the desired yaw rate under conditions where the wheelbase is constantly changing, the controller needs to be able to adjust the control amount in real time according to the change in wheelbase. Wheel-leg vehicles use a distributed drive method, which can directly control the longitudinal force of the tire by controlling the motor torque, thereby controlling the additional yaw moment formed by the longitudinal force. The sliding mode control can better adapt to the changes of parameters such as wheelbase, and has strong robustness. The yaw rate controller is used to add yaw torque. To control the variable, a sliding mode variable structure controller is designed to achieve stable tracking of the desired yaw rate.

[0119] Simplifying the model into a 2-DOF model with lateral and rotational freedom around the Z axis, the dynamic equation can be written as: .

[0120] Wherein, M is the additional yaw moment including the sliding mode control variable, that is, the expected additional yaw moment. is the distance from the left front wheel to the center of mass. The left front wheel is subjected to lateral force. is the distance from the right front wheel to the center of mass. The right front wheel is subjected to lateral force. is the distance from the left rear wheel to the center of mass. The left rear wheel is subjected to lateral force. is the distance from the right rear wheel to the center of mass. The right rear wheel is subjected to lateral force. is the yaw angular acceleration.

[0121] The sliding surface is defined as: .

[0122] in, is the desired yaw rate, is the weight factor, and s is the longitudinal slip rate of the tire. is the yaw angular velocity, For the accumulated time.

[0123] Combined with the dynamic equation, the formula for defining the sliding surface can be derived: .

[0124] in, is the sliding mode approach rate. Represents the yaw moment of inertia of the wheel-legged vehicle. is the desired yaw rate.

[0125] The additional yaw moment including the sliding mode control variable is obtained as: .

[0126] Where, M is the expected additional yaw moment; represents the yaw moment of inertia of the wheel-legged vehicle; is the desired yaw rate; is the expected yaw angular acceleration; Yaw angular velocity; is the weight factor; is the distance from the left front wheel to the center of mass; The left front wheel is subjected to lateral force; is the distance from the right front wheel to the center of mass; The right front wheel is subjected to lateral force; is the distance from the left rear wheel to the center of mass; The left rear wheel is subjected to lateral force; is the distance from the right rear wheel to the center of mass; The right rear wheel is subjected to lateral force; is the sliding mode approach rate calculated based on the tire model.

[0127] Step S6: Acquire the actual longitudinal speed and actual joint angle of the target wheel-legged vehicle.

[0128] Step S7: applying PID control theory according to the desired longitudinal speed and the actual longitudinal speed to obtain the total driving force.

[0129] In practical applications, the main control target of the longitudinal speed controller is to track the longitudinal speed of the wheel-legged vehicle. The target speed is generated by the operator's input. The speed controller uses classic PID closed-loop control. The actual speed Deviation Calculate the total driving force .

[0130] .

[0131] in, is the proportionality coefficient. is the integration coefficient. is the gain factor.

[0132] Step S8: According to the expected joint rotation angle and the actual joint angle, the PD control theory is applied to calculate the expected driving torque of the joint.

[0133] In practical applications, the variable wheelbase controller selects kinematic control, and calculates the desired hip and knee angles based on the known wheel center position through trajectory planning. The actual hip angle Deviation Calculate the driving torque of the hip joint , the same applies to the knee joint.

[0134] .in, is the proportionality coefficient, is the gain coefficient, The desired driving torque of the joint.

[0135] Step S9: Calculate the expected driving torque of the wheel according to the total driving force and the expected additional yaw moment.

[0136] In practical applications, a yaw rate controller is designed based on sliding mode control, and a longitudinal velocity controller is designed based on PID control to obtain the desired longitudinal resultant force and additional yaw moment. The lower-level controller needs to solve the wheel motor output torque based on the expected value to achieve the upper-level control target. Tire longitudinal force matrix Vertical synergy with expectations , expected additional yaw moment The relationship can be expressed as:

[0137] .

[0138] .

[0139] .

[0140] In the formula, , is the coefficient matrix, It is the lateral distance from the wheel center to the center of mass. is a 2-dimensional vector, is a 4-dimensional vector, and the longitudinal forces of the tires are independent of each other. There are multiple sets of solutions that satisfy the constraints for the upper control objectives.

[0141] Step S10: Taking minimizing the error as the first optimization objective function and minimizing the sum of the wheel adhesion utilization as the second optimization objective function, the optimal solution is determined from the expected driving torque of the wheel, the expected motor torque of the wheel is obtained, and the motor corresponding to the target wheel-legged vehicle is controlled according to the expected driving torque of the joint and the expected motor torque.

[0142] In practical applications, the purpose of control distribution is to distribute the desired longitudinal force and yaw moment to the four wheel motors. The optimization objectives are to minimize the control distribution error and tire adhesion utilization, and multi-objective optimization is performed.

[0143] According to the optimal control form, the cost function with minimizing the error as the optimization goal is: In the formula, is the weight factor.

[0144] Based on the tire friction circle principle, the lower the tire adhesion utilization rate, the larger the tire force space provided, so the cost function of the quadratic programming with the sum of the four tire adhesion utilization rates as the optimization target is: .

[0145] Taking into account the control error and tire adhesion utilization, the following optimization function is obtained: .

[0146] in, Control allocation error for desired longitudinal force and yaw moment distribution to wheel motors. is the coefficient matrix, It is the lateral distance from the wheel center to the center of mass. is the tire longitudinal force matrix. is a 2-dimensional vector. is the weight factor. Expected vertical force. is the desired additional yaw moment. The left front wheel is subjected to longitudinal force. The longitudinal force on the right front wheel. The left rear wheel is subjected to longitudinal force. The right rear wheel is subjected to longitudinal force. It is the sum of tire adhesion utilization. During the turning process of wheel-legged vehicles, the tires are subjected to longitudinal force. is the vertical force on the tire of the wheel-legged vehicle during the steering process. c is the optimization target weight factor. is the road adhesion coefficient.

[0147] The longitudinal force of each tire obtained through optimization should be less than the maximum longitudinal force that the ground can provide, that is: .

[0148] The tire longitudinal force obtained through quadratic programming needs to be realized through the wheel motor torque. According to the dynamic equation, the motor torque of each wheel is: .

[0149] in, is the motor torque of each wheel. is the acceleration of each tire. is the moment of inertia of the tire.

[0150] The actual control torque signal in step S10 is input to the joint motor and the wheel motor to complete the entire variable wheelbase speed difference steering movement. Figure 6 As shown. Figure 6 middle, To change the wheelbase size as desired. is the expected duration of the change process. Desired yaw rate. is the expected longitudinal velocity. is the expected change in the wheel center relative to the center of mass. The hip rotation angle. The knee joint angle. is the actual wheel center position change. is the longitudinal speed. is the lateral speed. is the yaw angular velocity. is the total yaw moment. is the total longitudinal force. is the joint torque. is the wheel torque.

[0151] Based on the motion control method for variable wheelbase speed difference steering of a wheel-leg type vehicle provided by the present invention, as Figure 7 As shown, the present invention also provides a motion control system for variable wheelbase speed difference steering applied to wheel-leg type vehicles, including: an environment perception information extraction and path planning module, a wheel end trajectory planning module, a kinematic solution module, a joint and wheel control module and a feedback module.

[0152] The environment perception information extraction and path planning module is used to obtain environmental information and determine the starting time of the wheelbase change and the rate of the wheelbase change process according to the path planning requirements.

[0153] The wheel-end trajectory planning module plans the trajectory of the wheel-end position based on a cubic polynomial, solves the tire force according to the expected vehicle longitudinal speed and yaw angular velocity, and corrects the wheel motor output torque according to the wheel longitudinal force distribution optimization.

[0154] The kinematics solving module solves the desired wheel end trajectory into the desired joint angle by combining the desired wheel end longitudinal and vertical trajectories through the kinematic vector method and the inverse kinematics relationship of the leg.

[0155] The joint and wheel control module is used to obtain the corresponding actual control torque through the longitudinal vehicle speed sliding mode controller and the wheel and joint PID controllers based on the desired joint angle, joint angular velocity, wheel speed, wheel angle and the feedback joint angle, joint angular velocity, wheel speed, wheel angle.

[0156] The feedback module is used to input the actual angles and angular velocities of the hip joint and the knee joint into the joint controller, and input the actual wheel speed and wheel angle into the wheel controller.

[0157] The method of the present invention focuses on three aspects: wheel-end trajectory planning, kinematics solution, and joint and wheel control. Through the method and system provided by the present invention, the wheel-legged vehicle can complete variable wheelbase speed difference steering, efficiently track the desired steering trajectory, and improve the maneuverability and terrain passing performance of the wheel-legged vehicle.

[0158] Due to structural limitations, wheel-legged vehicles cannot use the Ackerman steering method. Speed ​​differential steering limits the vehicle's maneuverability and passability. A larger turning radius at different speeds places great performance demands on tires and wheel motors, which is not conducive to the high dynamics of the vehicle. The motion control method and system for variable wheelbase speed differential steering of wheel-legged vehicles proposed in the present invention are as follows: Figure 8 As shown, by coordinating the compound action of the joint motor and the wheel motor, the effect of variable wheelbase speed difference steering is achieved, thereby improving the vehicle's passability and maneuverability.

[0159] The advantages of the obstacle crossing method proposed in the present invention are as follows: The present invention is analogous to traditional speed differential steering and Ackerman steering. The variable wheelbase speed differential steering described in the present invention can improve the steering ability of the speed differential steering when the mechanical structure space is insufficient to arrange the Ackerman steering, such as relatively large cornering conditions during driving, so that the wheel-legged vehicle has stronger passability. The speed differential steering is limited by the longitudinal driving force provided by the tires, making it difficult to generate a large yaw angular velocity, so that the steering ability is limited. This method utilizes the variable wheelbase characteristic of the wheel-legged vehicle. While performing the speed differential steering, the wheelbase size on both sides of the wheel-legged vehicle is changed, thereby improving the steering ability of the wheel-legged vehicle and reducing the output demand for the wheel motor.

[0160] Embodiment 2: A computer device comprises: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the motion control method for variable wheelbase speed difference steering of a wheel-leg type vehicle in Embodiment 1.

[0161] Embodiment 3: A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the motion control method for variable wheelbase speed difference steering of a wheel-leg type vehicle in Embodiment 1.

[0162] Embodiment 4: A computer program product, comprising a computer program, which, when executed by a processor, implements the motion control method for variable wheelbase speed difference steering of a wheel-leg type vehicle in Embodiment 1.

[0163] Embodiment 5: A computer device, which may be a database, and its internal structure diagram may be as follows: Fig.10 As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, referred to as I / O) and a communication interface. The processor, the memory and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store pending transactions. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, the motion control method of the wheel-leg type vehicle with variable wheelbase speed difference steering in Example 1 is implemented.

[0164] It should be noted that the object information (including but not limited to object device information, object personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in the present invention are all information and data authorized by the object or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant laws, regulations and standards of relevant countries and regions.

[0165] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided by the present invention can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided by the present invention may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided by the present invention may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but are not limited to this.

[0166] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0167] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A motion control method for variable wheelbase speed difference steering of a wheel-legged vehicle, characterized in that: The method comprises: Obtaining a desired longitudinal velocity and a desired yaw angular velocity; Determine the expected motion trajectory of the wheel center according to the path planning of the target wheel-legged vehicle; Determine the expected motion trajectory of the wheel center according to the path planning of the target wheel-legged vehicle, specifically including: constructing a first hip joint coordinate system; the first hip joint coordinate system takes the contact position between the target wheel-legged vehicle and the leg as the origin, the contact surface between the target wheel-legged vehicle and the leg as the horizontal plane, the direction perpendicular to the horizontal plane as the vertical direction of the wheel, and the motion direction of the target wheel-legged vehicle as the longitudinal direction of the wheel; calculate the position coordinates of the wheel center in the first hip joint coordinate system according to the positional relationship between the hip joint, the knee joint and the wheel; determine the coordinates of the initial position and the coordinates of the target position according to the path planning of the target wheel-legged vehicle; according to the expected longitudinal speed and the position coordinates, and the speed of the initial position and the target position is zero, apply a cubic polynomial interpolation function to obtain the expected motion trajectory of the wheel center; Calculating the expected joint angles of the joints of the target wheel-legged vehicle according to the expected motion trajectory of the wheel center; the joints include hip joints and knee joints; Constructing a dynamic model of the target wheel-legged vehicle; According to the dynamic model of the target wheel-legged vehicle and the desired yaw angular velocity, the sliding mode control theory is applied to obtain the desired additional yaw moment; Obtaining the actual longitudinal speed and actual joint angle of the target wheel-legged vehicle; According to the desired longitudinal speed and the actual longitudinal speed, a PID control theory is applied to obtain a total driving force; According to the desired joint rotation angle and the actual joint angle, the desired driving torque of the joint is calculated by applying PD control theory; Calculating a desired driving torque of the wheel according to the total driving force and the desired additional yaw moment; Taking minimizing the error as the first optimization objective function and minimizing the sum of the wheel adhesion utilization as the second optimization objective function, the optimal solution is determined from the expected driving torque of the wheel, the expected motor torque of the wheel is obtained, and the motor corresponding to the target wheel-legged vehicle is controlled according to the expected driving torque of the joint and the expected motor torque.

2. The motion control method for variable wheelbase speed difference steering of a wheel-leg type vehicle according to claim 1, characterized in that: The target wheel-legged vehicle includes front wheels and rear wheels; The desired joint angle of the hip joint of the front wheel is: The desired joint angle of the knee joint of the front wheel is: The desired joint angle of the hip joint of the rear wheel is: The desired joint angle of the knee joint of the rear wheel is: in, is the desired joint angle of the hip joint of the front wheel; is the desired joint angle of the knee joint of the front wheel; is the desired joint rotation angle of the hip joint of the rear wheel; is the expected joint rotation angle of the knee joint of the rear wheel; l1 is the thigh length of the target wheel-legged vehicle, l2 is the calf length of the target wheel-legged vehicle; (x3, y3) is the position coordinate of the wheel center of the target wheel-legged vehicle; q2 is the joint rotation angle of the knee joint of the target wheel-legged vehicle.

3. The motion control method for variable wheelbase speed difference steering of a wheel-leg type vehicle according to claim 1, characterized in that: The dynamic model of the target wheel-legged vehicle includes a longitudinal dynamic equation of the wheel-legged vehicle, a lateral dynamic equation of the wheel-legged vehicle, and a yaw dynamic equation of the wheel-legged vehicle; The longitudinal dynamic equation of the wheel-legged vehicle is: The lateral dynamic equation of the wheel-legged vehicle is: The yaw dynamics equation of a wheel-legged vehicle is: u represents the longitudinal velocity, v represents the lateral velocity, ω represents the yaw angular velocity, I z represents the yaw moment of inertia of the wheel-legged vehicle, d represents the lateral distance from the wheel center to the center of mass; The tires of wheel-legged vehicles are subjected to lateral forces during the turning process; The tires of wheel-legged vehicles are subjected to longitudinal forces during the steering process; The longitudinal force on the left front wheel; The longitudinal force on the right front wheel; The longitudinal force of the left rear wheel; is the longitudinal force on the right rear wheel; m is the mass of the wheel-legged vehicle; is the longitudinal acceleration; F f is resistance; lf is the distance from the left front wheel to the center of mass; is the lateral force on the left front wheel; l rf is the distance from the right front wheel to the center of mass; is the lateral force on the right front wheel; l lr is the distance from the left rear wheel to the center of mass; is the lateral force on the left rear wheel; l rr is the distance from the right rear wheel to the center of mass; The right rear wheel is subjected to lateral force; is the lateral acceleration; is the yaw angular acceleration.

4. The motion control method for variable wheelbase speed difference steering of a wheel-leg type vehicle according to claim 1, characterized in that: The desired additional yaw moment is: Where M is the expected additional yaw moment; I z represents the yaw moment of inertia of the wheel-legged vehicle; is the desired yaw rate; is the expected yaw angular acceleration; is the yaw rate; γ is the weight factor; l lf is the distance from the left front wheel to the center of mass; is the lateral force on the left front wheel; l rf is the distance from the right front wheel to the center of mass; is the lateral force on the right front wheel; l lr is the distance from the left rear wheel to the center of mass; is the lateral force on the left rear wheel; l rr is the distance from the right rear wheel to the center of mass; The right rear wheel is subjected to lateral force; is the sliding mode approach rate calculated based on the tire model.

5. The motion control method for variable wheelbase speed difference steering of a wheel-leg type vehicle according to claim 1, characterized in that: The first optimization objective function is: v d =[F d M d ] T ; Where J1 is the control allocation error of the desired longitudinal force and yaw moment allocated to the wheel motor; B is the coefficient matrix, d is the lateral distance from the wheel center to the center of mass; N F is the tire longitudinal force matrix; v d is a 2-dimensional vector; W1 is the weight factor; F d Expected longitudinal force; M d is the expected additional yaw moment; The longitudinal force on the left front wheel; The longitudinal force on the right front wheel; The longitudinal force of the left rear wheel; is the longitudinal force on the right rear wheel; T is the transposition.

6. The motion control method for variable wheelbase speed difference steering of a wheel-leg type vehicle according to claim 1, characterized in that: The second optimization objective function is: Among them, J2 is the sum of tire adhesion utilization; The tires of wheel-legged vehicles are subjected to longitudinal forces during the steering process; is the vertical force on the tire of the wheel-legged vehicle during the steering process; c is the optimization target weight factor; μ is the road adhesion coefficient.

7. A computer device comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the motion control method for variable wheelbase speed difference steering of a wheel-legged vehicle as described in any one of claims 1-6.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the motion control method for variable wheelbase speed difference steering of a wheel-leg type vehicle as described in any one of claims 1-6 is implemented.

9. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the motion control method for variable wheelbase speed difference steering of a wheel-leg type vehicle as described in any one of claims 1-6 is implemented.

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