A wheel-legged vehicle motion trajectory planning method, device, medium and product

Abstract

The application discloses a wheel-legged vehicle motion trajectory planning method and device, medium and product, and relates to the field of motion trajectory planning; the method comprises the following steps: acquiring basic information of a wheel-legged vehicle in a motion process; constructing a wheel-legged vehicle model; adopting a search algorithm based on a two-step method, screening a landing contact point according to the wheel-legged vehicle model and the basic information, and determining a landing contact point set; based on the landing contact point set, adopting a non-linear constraint solving method to perform trajectory optimization, and obtaining an optimized trajectory; the application can realize planning control on the trajectory of the wheel-legged vehicle motion.

Description

Technical Field

[0001] This application relates to the field of motion trajectory planning, and in particular to a method, device, medium, and product for planning the motion trajectory of a wheel-legged vehicle. Background Technology

[0002] Research in the field of quadruped robots has recently become increasingly popular, with numerous researchers focusing on the high-dynamic motion of these legged robots to improve the terrain mobility lacking in wheeled platforms. However, on flat terrain, the walking efficiency of quadruped robots is far inferior to that of wheeled platforms. Wheel-legged vehicles combine the advantages of wheeled platforms and quadruped robots, overcoming the limitations of wheeled platforms in overcoming obstacles through legged motion. On good terrain, they can increase their speed through wheeled drive, exhibiting strong terrain adaptability. Through jumping, a large-distance forward and upward displacement, wheel-legged vehicles can leap over higher obstacles or distant potholes; therefore, this motion has a significant impact on the terrain mobility and high-dynamic motion capabilities of wheel-legged vehicles.

[0003] The control problem of jumping motion is often transformed into a center-of-mass trajectory planning problem, combined with center-of-mass attitude control, and wheel-end trajectory planning and control, to ensure the attitude stability of wheel-legged vehicles during jumping. When wheel-legged vehicles encounter obstacles that are difficult to jump over, they can overcome the obstacle by combining jumping with climbing. That is, the wheel-legged vehicle first jumps to the edge of the obstacle, and then swings its legs and drive wheels to climb the obstacle. This method can complete obstacle crossing even when the joint performance of the wheel-legged vehicle is insufficient, and reduces jumping energy consumption. Therefore, how to plan and control the trajectory of wheel-legged vehicle motion is crucial. Summary of the Invention

[0004] The purpose of this application is to provide a method, device, medium, and product for planning the motion trajectory of wheeled vehicles, which can realize the planning and control of the motion trajectory of wheeled vehicles.

[0005] To achieve the above objectives, this application provides the following solution: a method for planning the motion trajectory of a wheel-legged vehicle, the method comprising: acquiring basic information of the wheel-legged vehicle during its motion; the basic information including: the distance from the center of mass of the wheel-legged vehicle to the obstacle and the height of the obstacle.

[0006] A wheel-legged vehicle model is constructed; the wheel-legged vehicle model includes: a leg kinematic model and a single rigid body model; the leg kinematic model is a physically simplified model obtained by projecting the wheel-legged vehicle onto the sagittal plane; the single rigid body model is a floating base dynamic model based on a two-dimensional planar simplification of the wheel-legged vehicle.

[0007] A two-step search algorithm is adopted to screen the landing contact points based on the wheel-leg vehicle model and the basic information to determine the set of landing contact points; the two-step method includes: three-dimensional box constraint of vehicle body posture and selection of optimal landing contact points for multiple objectives.

[0008] Based on the set of landing contact points, a nonlinear constraint solution method is used to optimize the trajectory and obtain an optimized trajectory. The nonlinear constraint solution includes a cost function and constraints corresponding to the obstacle jumping task. The optimized trajectory is used to provide an obstacle-crossing motion trajectory for wheel-legged vehicles to jump and climb.

[0009] Optionally, the mathematical expression of the single rigid body model specifically includes:

[0010]

[0011] Where, m CoM For the overall vehicle weight of wheel-legged vehicles; I θ ρ is the pitch inertia of the wheel-legged vehicle; g is the acceleration due to gravity; α is the slope angle of the terrain; T θ For pitching moment; This generates an additional driving load along the wheel tangent at the wheel end; θ is the vehicle body pitch angle. The longitudinal acceleration of the vehicle's center of mass in the world coordinate system; The vertical acceleration of the vehicle's center of mass in the world coordinate system; The pitch angle acceleration of the vehicle body; The longitudinal force exerted on the wheel end of the front or hind leg; This indicates the vertical force acting on the wheel end of the front or hind leg; m represents the front or hind leg; m = f represents the front leg; m = b represents the hind leg.

[0012] Optionally, the three-dimensional bounding box constraint of the vehicle body posture is determined based on the wheel-leg type vehicle model and the basic information; the three-dimensional bounding box constraint of the vehicle body posture specifically includes:

[0013]

[0014] Where ψ represents the 3D bounding box constraint of the vehicle body attitude; q CaM The degree of freedom for the vehicle's center of gravity; This indicates the distance from the center of gravity of a wheeled vehicle to an obstacle. Indicates the height of the obstacle; W x CoM is the x-coordinate corresponding to the position of the centroid; W Z CoM The vertical coordinates corresponding to the position of the centroid; Terrain is the basic information; δ x δ represents the increment in the dimension corresponding to the horizontal axis x; zδ is the increment in the dimension corresponding to the vertical axis z; θ The increment in dimension corresponding to the pitch angle θ of the vehicle body; θ is the pitch angle of the vehicle body; Collosion(·) is the function to determine whether the leg collides with the obstacle; The positions of the hip joints, knee joints, and wheel ends of the fore and hind legs in the world coordinate system; q Joint For all joint degrees of freedom; This represents the minimum value for all joint degrees of freedom. R is the maximum value of all joint degrees of freedom; H ​​is the vehicle height; ζ is the limit deformation of the tire; b is the hind leg. It is the space of real numbers; This refers to the longitudinal position of the rear wheel; This indicates the position of the front wheel in the height direction.

[0015] Optionally, the selection of the optimal landing contact point for multiple targets specifically includes:

[0016] Determine the objective function; the objective function includes a stability function and an energy function; the stability function is determined based on the position of the zero torque point relative to the support points of the front and rear wheels; the energy function is determined based on the energy consumption of the wheel-leg vehicle in the vertical direction of overcoming gravity during jumping motion.

[0017] Based on the three-dimensional bounding box constraints of the vehicle body posture and the objective function, sorting and filtering are performed to obtain the vehicle body posture space set.

[0018] Based on the three-dimensional bounding box constraints of the vehicle body posture, each vehicle body posture in the set of vehicle body posture spaces is traversed to calculate the position vector; the position vector is the position vector of the wheel end relative to the centroid in world coordinates.

[0019] Based on the sum of the position vector and the objective function, the optimal landing contact point for multiple objectives is selected to determine the set of landing contact points; the sum of the objective function is the sum of the stability function and the energy function.

[0020] Optionally, the cost function specifically includes:

[0021]

[0022] in, Q represents the weighted 2-norm; t Q is the total weight matrix of the trajectory; l Q is the weight matrix of the trajectory points at the moment of landing; v This is the weight matrix for the velocity term; To optimize the trajectory; For the landing time T L Optimized trajectory at time; pCoM This is the actual trajectory upon landing; J i Let p be the cost function corresponding to the i-th step size; N is the total number of step sizes; p CoM (T L ) is the landing time T L The actual landing trajectory at that time; For p CoM (T L The first derivative of ).

[0023] Optionally, the constraints include: single rigid body dynamics constraints, ZMP constraints during the extension phase, LAP point constraints, initial configuration, final configuration, joint angle constraints, joint moment constraints, contact sequence constraints, set constraints related to obstacle avoidance, and foot wheel positions when in contact with obstacle edges during landing and climbing phases.

[0024] Optionally, the single rigid body dynamic constraint specifically includes:

[0025]

[0026] Among them, T θ For pitching moment; W r m This is the position vector of the wheel end relative to the centroid in the world coordinate system; This is the position vector of the ground contact point relative to the centroid in the world coordinate system. This generates an additional driving load along the wheel tangential direction at the wheel end; α is the terrain slope angle; f m is the vector of frictional force at the wheel end of the front or hind leg; m is the front or hind leg; when m = f, it is the front leg; when m = b, it is the hind leg.

[0027] A computer device includes: 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 above-described wheel-legged vehicle motion trajectory planning method.

[0028] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-described method for planning the motion trajectory of a wheel-legged vehicle.

[0029] A computer program product includes a computer program that, when executed by a processor, implements the above-described method for planning the motion trajectory of a wheeled vehicle.

[0030] According to the specific embodiments provided in this application, the following technical effects are disclosed: This application discloses a method, device, medium, and product for planning the motion trajectory of a wheel-legged vehicle. For obstacle-crossing methods combining jumping and climbing, it combines obstacle information and vehicle posture with the dynamic model of the wheel-legged vehicle, considering both stability and energy efficiency to plan the optimal landing contact point (LAP point), and uses nonlinear optimization to obtain the optimal jumping trajectory, providing a foundation for obstacle-crossing methods combining jumping and climbing for wheel-legged vehicles; therefore, it can realize the planning and control of the motion trajectory of wheel-legged vehicles. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic flowchart of the wheel-leg vehicle motion trajectory planning method provided in an embodiment of this application.

[0033] Figure 2 A flowchart illustrating the steps of the wheel-leg vehicle trajectory planning method provided in this application embodiment in practical applications.

[0034] Figure 3 This is a simplified schematic diagram of a wheel-leg vehicle model provided in an embodiment of this application.

[0035] Figure 4 This is a schematic diagram of a single-leg model using the foreleg as an example, provided as an embodiment of this application.

[0036] Figure 5 A flowchart of the two-step method provided for embodiments of this application.

[0037] Figure 6 This is a system structure block diagram provided for an embodiment of this application. Detailed Implementation

[0038] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0039] The purpose of this application is to provide a method, device, medium, and product for planning the motion trajectory of wheeled vehicles, which aims to realize the planning and control of the motion trajectory of wheeled vehicles.

[0040] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, this application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Example 1: As Figure 1 As shown in this embodiment, the method for planning the motion trajectory of a wheel-legged vehicle includes the following steps.

[0042] Step 100: Obtain basic information about the wheel-legged vehicle during its movement. This basic information includes the distance from the vehicle's center of gravity to the obstacle and the height of the obstacle.

[0043] Step 200: Construct the wheel-leg vehicle model. The wheel-leg vehicle model includes: a leg kinematic model and a single rigid body model; the leg kinematic model is a physically simplified model obtained by projecting the wheel-leg vehicle onto the sagittal plane; the single rigid body model is a floating base dynamic model based on a two-dimensional planar simplification of the wheel-leg vehicle.

[0044] Step 300: A two-step search algorithm is used to filter landing contact points based on the wheel-leg vehicle model and basic information to determine the set of landing contact points. The two-step method includes: three-dimensional bounding box constraints for vehicle body posture and selection of optimal landing contact points for multiple objectives.

[0045] Step 400: Based on the set of landing contact points, trajectory optimization is performed using a nonlinear constraint solution method to obtain the optimized trajectory. The nonlinear constraint solution includes: the cost function and the constraints corresponding to the obstacle jumping task; the optimized trajectory is used to provide the obstacle-crossing motion trajectory when the wheel-legged vehicle jumps and climbs.

[0046] The mathematical expression for a single rigid body model includes the following formulas.

[0047]

[0048] Where, m CoM For the overall vehicle weight of wheel-legged vehicles; I θ ρ is the pitch inertia of the wheel-legged vehicle; g is the acceleration due to gravity; α is the slope angle of the terrain; T θ For pitching moment; This generates an additional driving load along the wheel tangent at the wheel end; θ is the vehicle body pitch angle. The longitudinal acceleration of the vehicle's center of mass in the world coordinate system; The vertical acceleration of the vehicle's center of mass in the world coordinate system; The pitch angle acceleration of the vehicle body; The longitudinal force exerted on the wheel end of the front or hind leg; This indicates the vertical force acting on the wheel end of the front or hind leg; m represents the front or hind leg; m = f represents the front leg; m = b represents the hind leg.

[0049] The 3D bounding box constraint for vehicle body posture is determined based on the wheel-leg type vehicle model and basic information; the 3D bounding box constraint for vehicle body posture specifically includes the following formulas.

[0050]

[0051] Where Ψ represents the 3D bounding box constraint for the vehicle body attitude; q CoM The degree of freedom for the vehicle's center of gravity; This indicates the distance from the center of gravity of a wheeled vehicle to an obstacle. Indicates the height of the obstacle; W x CoM is the x-coordinate corresponding to the position of the centroid; W Z CoM The vertical coordinates corresponding to the position of the centroid; Terrain is the basic information; δ x δ represents the increment in the dimension corresponding to the horizontal axis x; z δ is the increment in the dimension corresponding to the vertical axis z; θ The increment in dimension corresponding to the pitch angle θ of the vehicle body; θ is the pitch angle of the vehicle body; Collision(·) is the function to determine whether the leg collides with the obstacle; The positions of the hip joints, knee joints, and wheel ends of the fore and hind legs in the world coordinate system; q Joint For all joint degrees of freedom; This represents the minimum value for all joint degrees of freedom. R is the maximum value of all joint degrees of freedom; H ​​is the vehicle height; ζ is the limit deformation of the tire; b is the hind leg. It is the space of real numbers; The longitudinal position of the rear wheel; This indicates the position of the front wheel in the height direction.

[0052] In one embodiment, the selection of the optimal landing contact point for multiple targets specifically includes the following steps.

[0053] Determine the objective function; the objective function includes: stability function and energy function; the stability function is determined based on the position of the zero torque point relative to the support points of the front and rear wheels; the energy function is determined based on the energy consumption of the wheel-leg vehicle in the vertical direction to overcome gravity during jumping motion.

[0054] Based on the 3D bounding box constraints of the vehicle body posture and the objective function, sorting and filtering are performed to obtain the set of vehicle body posture spaces.

[0055] Based on the 3D bounding box constraints of the vehicle body posture, traverse each vehicle body posture in the vehicle body posture space set and calculate the position vector; the position vector is the position vector of the wheel end relative to the centroid in world coordinates.

[0056] Based on the sum of the position vector and the objective function, the optimal landing contact point is selected for multiple objectives, and the set of landing contact points is determined; the sum of the objective function is the sum of the stability function and the energy function.

[0057] The cost function includes the following formula.

[0058]

[0059] in, Q represents the weighted 2-norm; t Q is the total weight matrix of the trajectory; l Q is the weight matrix of the trajectory points at the moment of landing; v This is the weight matrix for the velocity term; To optimize the trajectory; For the landing time T L Optimized trajectory at time; p CoM This is the actual trajectory upon landing; J i Let p be the cost function corresponding to the i-th step size; N is the total number of step sizes; p CoM (T L ) is the landing time T L The actual landing trajectory at that time; For p CoM (T L The first derivative of ).

[0060] The constraints include: single rigid body dynamics constraints, ZMP constraints during the extension phase, LAP point constraints, initial configuration, final configuration, joint angle constraints, joint moment constraints, contact sequence constraints, set constraints related to obstacle avoidance, and foot wheel positions when in contact with obstacle edges during landing and climbing phases.

[0061] Single rigid body dynamic constraints specifically include the following formulas.

[0062]

[0063] Among them, T θ For pitching moment; W r m This is the position vector of the wheel end relative to the centroid in the world coordinate system; This is the position vector of the ground contact point relative to the centroid in the world coordinate system. This generates an additional driving load along the wheel tangential direction at the wheel end; α is the terrain slope angle; m is the front leg or rear leg; m = f for the front leg; m = b for the rear leg; f mThis is the vector of frictional force at the wheel end of the front or hind leg.

[0064] In practical applications, the flowchart corresponding to the method provided in this application can be found here. Figure 2 The details are as follows.

[0065] Step 1: Measure the distance from the center of gravity of the wheel-leg vehicle to the obstacle and the height of the obstacle using sensors.

[0066]

[0067] in, This indicates the distance from the center of gravity of a wheeled vehicle to an obstacle. Indicates the height of the obstacle. Terrain is the base information.

[0068] Step 2: Establish the forward kinematics model and single rigid body model of the leg of the wheel-leg vehicle to lay the model foundation for subsequent optimization solutions.

[0069] ① Establish a leg kinematic model. The wheel-legged vehicle is projected onto the sagittal plane to simplify the model. The simplified wheel-legged vehicle model is as follows: Figure 3 As shown.

[0070] {W} represents the world coordinate system, the floating coordinate system {B} is fixedly connected to the center of mass of the vehicle body, and θ is the pitch angle of the vehicle body. The rotation matrix between the world coordinate system and the floating coordinate system is... W R B As shown below.

[0071]

[0072] These represent the ground forces acting on the front and rear wheels, respectively, and are vectors. This includes the aforementioned ground forces, namely This is the vector consisting of the ground forces acting on the front wheels; Let be the vector of the ground forces acting on the rear wheels. The degrees of freedom of the vehicle's center of mass can be expressed as: Figure 4 It is a single-leg model using the front leg as an example. Let be the generalized coordinate vectors of the hip and knee joints of the front leg and the wheel. When the subscript is 'b', it corresponds to the generalized vectors of the joints (hip and knee joints) of the hind leg and the wheel. All joint degrees of freedom can be represented as: All wheel degrees of freedom can be expressed as

[0073] In this 2D plane, the state vector q and the generalized velocity vector u of the wheel-leg vehicle are represented as follows.

[0074]

[0075] in[ W x CoM W Z CoM ] T It is the location of the center of mass. W vx CoM W vZ CoM ] T Describe the velocity of the center of mass. For the transpose of the degree of freedom of the vehicle's center of gravity; T stands for transpose; This is a transposition of the joint degrees of freedom; θ is the transpose of the wheel's degree of freedom; θ is the pitch angle of the vehicle body. The first derivative of θ; For q Joint The first derivative; For q Wheel The first derivative.

[0076] Positive leg kinematics is used to describe the relative positional relationship between the wheel end and the hip joint of the leg. Figure 4 Taking the foreleg as an example, key symbols are marked. The structural parameters of the wheel-legged vehicle are known and invariant, and there is no relative positional difference between its hip joint and center of mass in the Z-direction floating base coordinate system. Therefore, the feasible region for foot placement can be analyzed using single-leg kinematics in the floating base coordinate system. The position vector of the knee joint relative to the hip joint in the floating base coordinate system can be calculated from geometric relationships. The position vector of the wheel end relative to the hip joint for:

[0077]

[0078] For equation (5) Taking the partial derivative yields the Jacobian matrix J. m .

[0079]

[0080] in, Let l be the state vector of the knee joint; u The distance from the hip joint to the knee joint; l l The distance from the hip joint to the wheel end (wheel); This is the state vector of the hip joint.

[0081] The positions of the hip joint, knee joint, and wheel end in the world coordinate system can more intuitively determine the collision between the leg and the obstacle, as described below.

[0082]

[0083] In the formula, lh It is the distance from the hip joint to the center of mass. This refers to the position of the knee joint; This refers to the position of the hip joint; This refers to the position of the wheel end (wheel).

[0084] ②Establish a single rigid body model for the wheel-legged vehicle. The floating base dynamic model simplified by two-dimensional plane still has a certain degree of nonlinearity. Applying formula (5) to optimization problems with a large number of iterations will increase the computational load. Therefore, a dynamic model that is as linear as possible needs to be established. The single rigid body model has been proven to be feasible in the application of quadruped robots. This model ignores the mass of the leg system and only considers the force on the vehicle body without losing the dynamic relationship.

[0085] Wheel-leg vehicles can actively drive their wheels, resulting in additional driving loads along the wheel tangent at the wheel tip. The wheel-obstacle contact model uses a rigid body contact approach. This model only differs significantly from the wheel-leg model under extreme yaw motion conditions. The problem discussed in this paper is conducted in the sagittal plane, so lateral and yaw motions are not required; therefore, a rigid body-to-rigid body contact approach is sufficient. Ignoring the small rotational inertia of the wheel, this additional force... The ideal wheel contact condition is represented as follows.

[0086]

[0087] In the formula, R is the wheel radius. This is the rated torque of the wheel.

[0088] Then, the standard single rigid body dynamics equations were modified, and the model is defined as follows.

[0089]

[0090] In the formula, m CoM ,I θ Let g be the total mass of the wheel-legged vehicle and α be the pitch inertia, respectively; g is the acceleration due to gravity; and α is the terrain slope angle. In the problem studied in this application... It has only two possible values. Pitch moment T θ It is given by equation (9).

[0091]

[0092] In the formula, This represents the position vector of the wheel end relative to the center of mass in the world coordinate system. This represents the position vector of the ground contact point relative to the centroid in the world coordinate system. It is the outer product operation of two-dimensional vectors. It is worth emphasizing that when the contact sequence of each leg is 0, it indicates that the leg is airborne, and at this time f... m =0 at the same time

[0093] Step 3: Find the optimal landing attachment point (LAP) based on the two-step method. Determining the position of the center of mass, attitude, and wheel end position at the moment of landing is crucial. For ease of subsequent description, the point at the moment of landing is defined as the landing attachment point (LAP), and the physical quantities contained in this point are expressed by equation (10).

[0094]

[0095] in, W x land , W z land This indicates the sagittal plane position of the landing point in the world coordinate system. W θ land It is the pitch angle of the wheel-legged vehicle at the point of contact in the world coordinate system. This represents the position vector of the wheel ends of the front and rear legs relative to the center of mass of the wheel-leg vehicle in the world coordinate system.

[0096] As a critical transition point, the LAP (Leg-Aperture Point) requires careful consideration of energy consumption and stability factors for wheel-legged vehicles. Based on the theory of the polygonal stability domain of the support point, the location of the LAP point must at least satisfy the following conditions.

[0097]

[0098] Here, H represents the vehicle height, not the standing height. To ensure the static stability of the wheel-legged vehicle at the moment of landing, it is necessary to minimize the values ​​describing the vehicle's attitude at the LAP point, as these physical quantities are directly related to the vehicle's potential and kinetic energy. To find a suitable LAP and reduce the search time, this application constructs a two-step search algorithm, the flowchart of which is shown below. Figure 5 As shown.

[0099] ① Construct a 3D bounding box constraint for the vehicle body attitude. By setting kinematic constraints, the set of states that meet the conditions is... The collection process is carried out, and the set of states can be represented as follows.

[0100]

[0101] In the formula, δ x ,δ z ,δ θThese are increments in each dimension, and their inequalities constitute the box constraints. Collision(·) is the function that determines whether a leg collides with an obstacle. This represents the positions of the hip and knee joints of the fore and hind legs, and the wheel ends in the world coordinate system. The basic principle of the collision function is that, in the sagittal plane, the obstacle edge can be viewed as two line segments intersecting at the obstacle vertices. Collision determination can be transformed into the question of whether the line segments formed by the hip and knee joints, and the line segments formed by the knee joint and the wheel ends, intersect with the obstacle edge line segments. In addition, the front and hind leg wheels are required to be in close contact with the obstacle edge, and the compression of the wheels cannot exceed the tire's limit deformation ζ. Simultaneously, constraints on the range of joint angles are necessary. Although the traversal of posture and joint angles is extensive during the construction of the state set containing the above constraints, the calculations involved are relatively simple.

[0102] ② LAP Point Selection Based on Multi-Objective Optimization. After constructing the ψ set that meets the conditions, the two objectives of optimal stability and minimum energy consumption were selected, and the elements in the set were further refined. The zero-moment point (ZMP) can more accurately characterize the stability of the wheel-leg vehicle than the center-of-mass projection point. When the wheel-leg vehicle lands at the LAP point, the pitch inertia of the vehicle body will cause instability in the vehicle state, and the zero-moment point (ZMP) is very likely to be outside the line connecting the front and rear support points. The wheel action will play a key role in this stage, and the change in the ZMP point position caused by the additional force provided by the wheels will be considered. In this problem, we only care about the position of the ZMP point in the sagittal plane at the moment of landing. Assuming that the front and rear leg wheel ends are in good contact with the edge of the obstacle at this moment, the relative position of this point in the X direction between the world coordinate system and the center of mass of the wheel-leg vehicle can be obtained according to the definition of ZMP. W x ZMP as follows.

[0103]

[0104] When the ZMP point lies on the line connecting the support points, it indicates that the wheel-leg vehicle is relatively stable. Static ZMP analysis reflects the sensitivity of using wheel actuation to improve vehicle stability to different center-of-gravity and leg postures, indirectly indicating the level of stability. Therefore, the stability score is defined as the position of the ZMP point relative to the midpoint of the front and rear wheel supports. A higher score indicates that using wheel actuation in the current posture is more effective in preventing the vehicle from pitching backward and becoming unstable. Stability Score ZMP It is represented as follows.

[0105]

[0106] Among them, Wr f (1) is the position of the rear wheel end relative to the center of mass in the world coordinate system.

[0107] Based on comprehensive considerations, an energy minimization score is also proposed. This score primarily depends on the relative position of the wheel-leg vehicle's center of gravity height within the box constraints. This is because the vehicle must overcome gravity in the vertical direction during jumping motion, and compared to the other two degrees of freedom of the center of gravity in the sagittal plane, its energy consumption accounts for the vast majority. Energy Minimization Score Energy It can be represented as follows.

[0108]

[0109] Total Score Sum It can be represented as the sum of the scores for two objectives, as follows.

[0110] Score Sum =λ ZMP Score ZMP +λ Energy Score Energy (16).

[0111] Where, λ ZMP ,λ Energy These are the weights for the stability score and the energy minimization score, respectively.

[0112] First, set the ground stiffness γ, the friction coefficient μ, and the rated torque of the wheel motor. Then, the elements in the ψ space are... W z CoM Sort in ascending order and select k groups with smaller vehicle body postures (degrees of freedom of the vehicle's center of gravity) q CoM This forms a new space Ω. For each set of poses within this new space, the constraints are calculated. W r m And calculate the overall score (total score). Sum The set of data with the highest score is selected as the LAP point.

[0113] Step 4: Jump Trajectory Optimization Based on Nonlinear Problems. For wheel-legged vehicles, the key to achieving a jump is appropriate trajectory planning. An optimization problem is established to find the attitude position trajectory of the center of mass, including its horizontal and vertical positions and the vehicle's tilt angle. The position trajectory of the wheel ends also needs to be planned. During the entire obstacle jump of a wheel-legged vehicle, it is difficult to have a suitable trajectory in advance for optimization, but it is feasible to pre-set the trajectory points at important moments in the movement. Therefore, the initial moment T of the wheel-legged vehicle's jump process is set... J Landing time T L and the end time T of the stretching process S The expected state at three instants. For the wheel-legged vehicle at the initial moment T during the jump process J The desired state; For wheel-leg vehicles at the moment of landing T L The desired state; For the wheel-legged vehicle at the end of the extension process, T S The desired state. Without loss of generality, the trajectory used for optimization... It can be represented as follows.

[0114]

[0115] Among them, PLInterp(·) is a piecewise linear interpolation operation.

[0116] The cost function is applied in the conventional quadratic form, and this nonlinear optimization problem can be defined as shown in equation (18). Specifically, it includes the following three parts. First, minimization:

[0117]

[0118] Then, search for:

[0119]

[0120] Finally, make it obey:

[0121] c(X)≤0h(X)=0.

[0122] in, Let Q represent the weighted 2 norm. t Q l These are the weight matrices for the entire trajectory and the weight matrix for the trajectory points at the moment of landing, respectively. This is the transpose of the position vector of the front leg wheel end relative to the center of mass in the world coordinate system; This is the transpose of the position vector of the rear leg wheel end relative to the center of mass in the world coordinate system.

[0123] Since the subsequent extension process requires the wheel-legged vehicle to stably and smoothly reach the LAP point, the weight at the moment of landing needs to be set to a relatively large value so that the obtained trajectory is within T... L The system should be kept as close as possible to the state set by LAP. A quadratic term for the instantaneous velocity upon landing is introduced into the cost function to enable the vehicle to land with less kinetic energy. Q v This is the weight matrix for the velocity term. The optimization variable X for the i-th step size... i This is related to single rigid body dynamics. c(X) and h(X) represent inequality constraints and equality constraints, respectively. The optimization step size is expressed as step = T. S / N.

[0124] For ease of representation, the origin of the world coordinate system is set at the ground projection point of the center of mass of the wheel-legged vehicle at the initial moment of optimization. The various constraints required for the obstacle-jumping task can be described as follows.

[0125] 1. Single rigid body dynamic constraints, see equation (9).

[0126] 2. ZMP constraints during the stretching phase.

[0127] 3. LAP point constraint: in

[0128] 4. Initial configuration:

[0129] q CoM (TJ) represents the initial time T during the jump process. J The degree of freedom of the vehicle's center of gravity; The vertical coordinate of the standard centroid.

[0130] 5. Final Configuration:

[0131] q CoM (T S () is the time T at the end of the extension process. S The degree of freedom in the vehicle's center of gravity.

[0132] 6. Joint angle limitations:

[0133] 7. Joint torque Limitations: τ max This represents the maximum joint torque.

[0134] 8. Contact sequence constraints: Contact sequence Cont = 1 for the preparation, landing, and extension phases. 1×4 ;Cont=0 contact sequence during the jump phase 1×4 .

[0135] 9. Set restrictions related to obstacle avoidance.

[0136] 10. Foot wheel position when in contact with the edge of the obstacle during landing and climbing phases.

[0137] More precisely, the optimization problem needs to satisfy the dynamic model, which will ensure that the planned trajectory is within the motion and driving capability range of the wheel-leg vehicle. Here, the single rigid body dynamic equation (9) is used as the constraint. The ZMP constraint for the extension phase is set, and the ZMP in the X direction is obtained through equation (15). It is expected to be located between the two wheel ends to obtain a trajectory that stabilizes the vehicle body. The LAP constraint will take effect before the landing time. It is hoped that the wheel-leg vehicle can reach the expected LAP point 5 steps in advance and maintain that position in the next few iterations. The initial configuration constraint is represented by the attitude of the wheel-leg vehicle in normal state, which is the height of the vehicle's center of mass in the world coordinate system in normal state. The end configuration constraint is also considered. At the end of the extension phase, the pitch angle and the standing height of the vehicle body are set to be the same as at the initial time. Soft constraints are set in the horizontal direction. This is very important. The horizontal distance traveled by the vehicle in the entire extension phase is related to the wheel speed. However, at this stage, the magnitude of the wheel speed cannot be strictly constrained because the wheel speed is related to the wheel torque. It is more important to emphasize the wheel torque that keeps the vehicle stable through the ZMP constraint. Joint angle constraints and W r m There is a kinematic relationship between them. The torque constraint is related to equations (6) and (9), and the torque can be represented by the ground reaction force and Jacobian matrix solved by the single rigid body model. The contact sequence Cont specifies the wheel-end contact situation at each stage. Geometric constraints are used to avoid collisions between the legs and body of the wheel-legged vehicle and obstacles, and the function Collision(·) is used here as well. The wheel-end position constraints in the landing and extension stages require the wheels to be close to the edge of the obstacle. The above nonlinear programming problem is established using the nonlinear optimization tool CasaDi, and then a multi-target algorithm is written to solve it.

[0138] This application also provides a wheel-legged vehicle motion trajectory planning system, which includes the following modules.

[0139] The obstacle information extraction module analyzes obstacle information and extracts information such as obstacle height and horizontal distance from the vehicle's center of gravity to the obstacle, providing a foundation for subsequent trajectory planning.

[0140] The landing contact point selection module, combined with the wheel-leg vehicle dynamics model, constructs a three-dimensional box constraint for the vehicle body posture and finds the optimal landing contact point based on a two-step method.

[0141] The jump trajectory optimization module pre-defines important trajectory points during the jump and, combined with vehicle dynamics model constraints, establishes an optimization problem to find the attitude position trajectory of the center of mass and the wheel end position trajectory. The system structure diagram is as follows: Figure 6 As shown.

[0142] To reduce the joint torque requirements during jumping and improve the obstacle-jumping ability of wheel-legged vehicles, this application provides a motion trajectory planning method for obstacle-jumping vehicles that incorporates climbing movements. First, a detailed description of the new jumping method and the floating basis dynamics and kinematic model of the wheel-legged vehicle is provided, and a single rigid body model considering wheel driving forces is established for model constraints in nonlinear problems. Second, a two-step optimal landing point state searcher and a trajectory optimizer based on nonlinear programming are proposed. These two components constitute the motion planner, which can generate offline center-of-mass and wheel-end trajectories that satisfy the dynamic characteristics of the wheel-legged vehicle, actuator capabilities, ZMP constraints, and terrain constraints for jumping.

[0143] Quadrupedal wheeled vehicles combine the terrain adaptability of a quadrupedal platform with the high-speed mobility of a wheeled platform, making them widely applicable. Typically, wheeled vehicles jump directly over obstacles, but this becomes difficult with larger obstacles. Combining jumping with climbing motions reduces the demands on joint torque and improves the obstacle-crossing capability. However, research on obstacle-crossing combining jumping and climbing for wheeled vehicles is currently scarce. This application proposes a trajectory planning method for obstacle-crossing that integrates climbing motions. By acquiring obstacle size information and the vehicle's own position information, the optimal landing contact point is selected, and nonlinear optimization is used to obtain the optimal trajectory. This method can be applied to obstacle-crossing by wheeled vehicles that integrate climbing motions.

[0144] The advantages of the method proposed in this application are as follows.

[0145] The obstacle-crossing ability of wheel-legged vehicles, which combines jumping and climbing movements, allows them to overcome more difficult obstacles, effectively improving the vehicle's terrain adaptability.

[0146] The dynamic model of the wheel-legged vehicle is integrated into the physical constraints of trajectory planning to ensure the basic dynamic performance of the planned trajectory. While fully considering the vehicle's attitude stability during the jumping process, energy consumption is also taken into account in the trajectory planning, so that the energy consumed in the jumping and climbing process is minimized, thereby improving the vehicle's energy economy while ensuring vehicle safety.

[0147] Example 2

[0148] A computer device includes: 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 wheel-leg vehicle motion trajectory planning method of Embodiment 1.

[0149] Example 3

[0150] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the wheel-legged vehicle motion trajectory planning method of Embodiment 1.

[0151] Example 4

[0152] A computer program product includes a computer program that, when executed by a processor, implements the wheel-legged vehicle motion trajectory planning method of Embodiment 1.

[0153] Example 5

[0154] A computer device, which may be a database, includes a processor, memory, input / output (I / O) interfaces, and a communication interface. The processor, memory, and I / O interfaces are connected via a system bus, and the communication interface is also connected to the system bus via the I / O interfaces. The processor provides computational and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage medium. The database stores pending transactions. The I / O interfaces facilitate information exchange between the processor and external devices. The communication interface enables communication with external terminals via a network connection. When executed by the processor, the computer program implements the wheel-legged vehicle trajectory planning method of Embodiment 1.

[0155] 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, data stored, data displayed, etc.) involved in this application are all information and data authorized by the object or fully authorized by all parties, and the collection, use and processing of related data must comply with the relevant laws, regulations and standards of the relevant countries and regions.

[0156] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application 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), magnetic 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. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0157] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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.

[0158] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A wheel-legged vehicle motion trajectory planning method, characterized in that, The method comprises: acquiring basic information of the wheel-legged vehicle during movement; the basic information comprises a distance from a center of mass of the wheel-legged vehicle to an obstacle and a height of the obstacle; constructing a wheel-legged vehicle model; the wheel-legged vehicle model comprises a leg kinematics model and a single rigid body model; the leg kinematics model is a physical simplified model obtained by projecting the wheel-legged vehicle into a sagittal plane; the single rigid body model is a floating base dynamics model obtained by simplifying the wheel-legged vehicle in a two-dimensional plane; adopting a searching algorithm based on a two-step method to screen a landing contact point according to the wheel-legged vehicle model and the basic information, and determine a landing contact point set; the two-step method comprises a vehicle body posture three-dimensional box constraint and a multi-objective optimal landing contact point selection; based on the landing contact point set, adopting a non-linear constraint solving method to perform trajectory optimization, and obtaining an optimized trajectory; the non-linear constraint solving comprises a cost function and a constraint condition corresponding to a jumping obstacle task; the optimized trajectory is used to provide an obstacle-crossing movement trajectory when the wheel-legged vehicle jumps and climbs; the vehicle body posture three-dimensional box constraint is determined according to the wheel-legged vehicle model and the basic information; the vehicle body posture three-dimensional box constraint specifically comprises: where ψ is the three-dimensional box constraint of the body posture; q CoM is the degree of freedom of the body mass center; represents the distance from the mass center of the wheel-legged vehicle to the obstacle, represents the height of the obstacle; W x CoM is the horizontal coordinate corresponding to the position of the mass center; W z CoM is the vertical coordinate corresponding to the position of the mass center; Terrain is the basic information; δ x is the increment in the dimension corresponding to the horizontal axis x; δ z is the increment in the dimension corresponding to the vertical axis z; δ θ is the increment in the dimension corresponding to the pitch angle θ of the body; θ is the pitch angle of the body; Collision(·) is a function for judging whether the leg collides with the obstacle; is the position of the front and rear leg hip joint, knee joint, and wheel end in the world coordinate system; q Joint is all joint degrees of freedom; is the minimum value of all joint degrees of freedom; is the maximum value of all joint degrees of freedom; R is the wheel radius; H is the body height; ξ is the limit deformation variable of the tire; b is the rear leg; is the real number space; is the longitudinal direction position of the rear wheel; is the height direction position of the front wheel; the multi-objective optimal landing contact point selection specifically comprises: determining an objective function; the objective function comprises a stability function and an energy function; the stability function is determined based on a position of a zero moment point relative to a front and rear wheel support point; the energy function is determined based on energy consumption required to overcome gravity in a vertical direction of the wheel-legged vehicle during jumping movement; performing sorting and screening processing according to the vehicle body posture three-dimensional box constraint and the objective function, and obtaining a vehicle body posture space set; traversing each vehicle body posture in the vehicle body posture space set according to the vehicle body posture three-dimensional box constraint, and calculating a position vector; the position vector is a position vector of a wheel end relative to a center of mass in a world coordinate; determining a landing contact point set by performing multi-objective optimal landing contact point selection according to the position vector and a target function sum; the target function sum is a sum of the stability function and the energy function.

2. The wheel-legged vehicle motion trajectory planning method according to claim 1, characterized in that, a mathematical expression of the single rigid body model specifically comprises: wherein, m CoM is the total mass of the wheel-legged vehicle; I θ is the pitch moment of inertia of the wheel-legged vehicle; g is the gravitational acceleration, and a is the terrain slope angle; T θ is the pitch moment; is the additional driving load generated at the wheel end along the tangent direction of the wheel; q is the pitch angle of the vehicle body; is the longitudinal acceleration of the vehicle center of mass in the world coordinate system; is the vertical acceleration of the vehicle center of mass in the world coordinate system; is the pitch angle acceleration of the vehicle body; is the longitudinal force on the front leg or the rear leg wheel end; represents the vertical force on the front leg or the rear leg wheel end; m is the front leg or the rear leg; m=f is the front leg; m=b is the rear leg.

3. The wheel-legged vehicle motion trajectory planning method according to claim 1, characterized in that, the cost function specifically comprises: in, Q represents the weighted 2-norm; t Q is the total weight matrix for the trajectory; l Q is the weight matrix of the trajectory points at the moment of impact; v This is the weight matrix for the velocity term; To optimize the trajectory; For the landing time T L Optimized trajectory at time; p CoM This is the actual trajectory upon landing; J i Let p be the cost function corresponding to the i-th step size; N is the total number of step sizes; p CoM (T L ) is the landing time T L The actual landing trajectory at that time; For p CoM (T L The first derivative of ).

4. The wheel-legged vehicle motion trajectory planning method according to claim 1, characterized in that, the constraint condition comprises a single rigid body dynamics constraint, a ZMP constraint in an extension stage, a LAP point constraint, an initial configuration, a final configuration, a joint angle limit, a joint torque limit, a contact sequence limit, a set limit related to obstacle avoidance, and a foot end wheel position when contacting an edge of an obstacle during landing and climbing stages.

5. The wheel-legged vehicle motion trajectory planning method according to claim 4, characterized in that, the single rigid body dynamics constraint specifically comprises: where T θ is the pitch moment; W r m is the position vector of the wheel end relative to the center of mass in the world coordinate system; is the position vector of the ground contact point relative to the center of mass in the world coordinate system; is the additional driving load generated by the wheel end along the tangent direction of the wheel; a is the terrain slope angle; f m is the wheel end friction force vector of the front leg or the rear leg; m is the front leg or the rear leg; m = f is the front leg; m = b is the rear leg.

6. A computer apparatus comprising: a memory and a processor to store a computer program stored on the memory and executable on the processor, characterized in that the processor executes the computer program to implement the wheel-legged vehicle movement trajectory planning method of any one of claims 1-5.

7. A computer-readable storage medium having stored thereon a computer program, characterized in that The computer program is executed by the processor to implement the wheel-legged vehicle movement trajectory planning method of any one of claims 1-5.

8. A computer program product comprising a computer program, characterized in that, The computer program, when executed by a processor, implements the wheel-legged vehicle motion trajectory planning method of any one of claims 1-5.

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