Control method of eight-degree-of-freedom wheel-legged robot

Abstract

The application provides a control method of an eight-degree-of-freedom wheel-legged robot, which comprises the following steps: S1. obtaining target control information of the eight-degree-of-freedom wheel-legged robot; the target control information comprises a target moving speed, a target rotating angle, a target height and a target rotating angular velocity; S2. determining a target advancing force according to the target moving speed and the target rotating angle; determining a target supporting force according to the target height, the target rotating angular velocity and the target rotating angle; S3. determining a target output torque of a wheel hub motor of the eight-degree-of-freedom wheel-legged robot according to the target advancing force; determining a target output torque of a swing arm motor of the eight-degree-of-freedom wheel-legged robot according to the target supporting force; S4. a controller in the eight-degree-of-freedom wheel-legged robot controls the wheel hub motor and the swing arm motor to output corresponding target output torques; through the control method, the robot can move according to a target advancing direction, a target speed and a target posture.

Description

Technical Field

[0001] This invention relates to the field of artificial intelligence, and more particularly to a control method for an eight-degree-of-freedom wheeled legged robot. Background Technology

[0002] Wheeled-legged robots are robots that combine the advantages of wheeled mobility and leg support, possessing strong obstacle-crossing capabilities and stability. These robots are widely used in fields such as industrial automation, rescue missions, disaster response, and home services.

[0003] Most wheeled-legged robots rely primarily on wheel drive in flat terrain, adjusting their posture through leg joint movements to maintain stability and minimize wheel lift-off, thereby improving speed and stability. Robot posture control is a key issue. Current research largely proposes control methods tailored to different structural characteristics. For example, two-wheeled-legged robots are often underactuated, with relatively simple structures, relying mainly on coordination between wheels and legs and joint flexibility for balance adjustment. They typically employ control models based on linear quadratic regulators to ensure stability. However, due to their underactuated nature, this structure has high requirements for balance and posture control, and its adaptability to complex terrain is relatively limited. Four-wheeled robots typically employ a tandem leg structure, possessing a large range of joint motion. They do not require dynamic balancing when all wheels are in contact with the ground, thus their attitude control focuses on accurately tracking the robot's posture. While this tandem structure offers good mobility and rapid adjustment capabilities, existing four-wheeled robots are mostly designed for smooth terrain control, exhibiting weak adaptability in complex terrains. The accuracy and stability of dynamic attitude adjustment still need improvement. Furthermore, some four-wheeled robots rely on complex mechanical structures and sensor systems, making lightweight design difficult. Their high dependence on computing resources also affects the system's real-time performance and stability.

[0004] Therefore, in order to solve the above-mentioned technical problems, it is urgent to propose a new technical approach. Summary of the Invention

[0005] In view of this, in order to improve the ability of wheeled-legged robots to traverse complex terrain and their posture balance control capabilities, this invention proposes a control method for an eight-degree-of-freedom wheeled-legged robot.

[0006] The present invention provides a control method for an eight-degree-of-freedom wheeled legged robot, comprising the following steps:

[0007] S1. Obtain target control information for the eight-DOF wheeled robot;

[0008] The target control information includes the target moving speed, target rotation angle, target height, and target rotation angular velocity;

[0009] S2. determining a target advancing force according to the target moving speed and the target rotation angle;

[0010] determining a target supporting force according to the target height, the target rotation angular speed and the target rotation angle;

[0011] S3. determining a target output torque of a wheel hub motor of the eight-degree-of-freedom wheel-legged robot according to the target advancing force;

[0012] determining a target output torque of a swing arm motor of the eight-degree-of-freedom wheel-legged robot according to the target supporting force;

[0013] S4. a controller in the eight-degree-of-freedom wheel-legged robot controls the wheel hub motor and the swing arm motor to output corresponding target output torques.

[0014] Further, the eight-degree-of-freedom wheel-legged robot comprises four wheel-legged structures, four swing arm motors, four wheel hub motors, a body and a controller;

[0015] The wheel-legged structure comprises a swing arm link and a wheel;

[0016] One end of the swing arm link is fixedly connected with the center of the wheel, and the other end of the swing arm link is connected with the power output end of the swing arm motor, for changing the posture of the eight-degree-of-freedom wheel-legged robot;

[0017] The wheel is connected with the power output end of the wheel hub motor, for changing the advancing direction and advancing speed of the eight-degree-of-freedom wheel-legged robot;

[0018] The swing arm motor and the wheel hub motor are both fixedly arranged on the body of the eight-degree-of-freedom wheel-legged robot and are in control connection with the controller;

[0019] One wheel-legged structure is correspondingly arranged around the body.

[0020] Further, before obtaining the target control information of the eight-degree-of-freedom wheel-legged robot, a center of mass coordinate system is further established, and the establishment method is as follows:

[0021] A center of mass coordinate system is established with the center of mass of the eight-degree-of-freedom wheel-legged robot as the origin, the positive direction of the Z-axis of the center of mass coordinate system is perpendicular to the body plane of the eight-degree-of-freedom wheel-legged robot and points upward, the positive direction of the X-axis of the center of mass coordinate system is parallel to the body plane of the eight-degree-of-freedom wheel-legged robot and points forward, and the Y-axis of the center of mass coordinate system is determined by the right-hand rule.

[0022] Further, the target moving speed comprises a target moving speed of the center of mass of the eight-degree-of-freedom wheel-legged robot on the X-axis

[0023] The target rotation angle includes a target rotation angle of the center of mass of the eight-degree-of-freedom wheel-legged robot rotating around the X axis A target rotation angle rotating around the Y axis And a target rotation angle rotating around the Z axis

[0024] The target height refers to a target height of the center of mass of the eight-degree-of-freedom wheel-legged robot on the Z axis

[0025] The target rotation angular velocity includes a target rotation angular velocity of the center of mass of the eight-degree-of-freedom wheel-legged robot rotating around the X axis And a target rotation angular velocity rotating around the Y axis

[0026] Further, the target forward force is obtained by the following steps:

[0027] S211. Based on the PD controller, according to the target moving speed of the center of mass on the X axis Calculate the target traction force F x ;

[0028]

[0029] Wherein, k pv represents the parameter of the PD controller, V x represents the actual speed of the center of mass in the X axis direction;

[0030] S212. Based on the PD controller, according to the target rotation angle rotating around the Z axis Calculate the target torque T z of the center of mass rotating around the Z axis;

[0031]

[0032] Wherein, k pw and k dw both represent the parameters of the PD controller, φ z represents the actual angle of the center of mass rotating around the Z axis, represents the actual angular velocity of the center of mass rotating around the Z axis;

[0033] S213. According to the target traction force F x And the target torque T z of the center of mass rotating around the Z axis, calculate the target forward force, the calculation formula is as follows:

[0034]

[0035] Wherein, F ω represents the target forward force, F ω1 , Fω2 , F ω3 , and F ω4 respectively correspond to the target forward force of the first to fourth hub motors, W 2,1 , W 2,2 , W 2,3 , and W 2,4 respectively correspond to the Y-direction distance from the rotation center to the center of mass of the first to fourth swing arm links;

[0036] The first hub motor refers to the hub motor on the left front of the eight-degree-of-freedom wheel-legged robot, and in counterclockwise order, the second hub motor, the third hub motor, and the fourth hub motor are arranged in sequence, and the swing arm links are arranged in the same order as the hub motors.

[0037] Further, the target support force is determined by the following method:

[0038] S221. Determine the target acceleration of the center of mass on the Z-axis according to the target height Determine the target angular acceleration of the center of mass around the X-axis according to the target angular velocity and the target angle of rotation and the target angular acceleration on the Y-axis

[0039] S222. Determine the theoretical attitude control matrix F target angular acceleration and d , the theoretical attitude control matrix is as follows:

[0040]

[0041] wherein F z represents the theoretical support force, F z1 , F z2 , F z3 , and F z4 represent the theoretical support force of the first to fourth swing arm motors, T x represents the target torque of the center of mass around the X-axis, T y represents the target torque of the center of mass around the Y-axis, m represents the mass of the eight-degree-of-freedom wheel-legged robot, I G represents the equivalent moment of inertia of the center of mass, and g represents the acceleration of gravity.

[0042] The first swing arm motor refers to the swing arm motor on the left front of the eight-degree-of-freedom wheel-legged robot, and in counterclockwise order, the second swing arm motor, the third swing arm motor, and the fourth swing arm motor are arranged in sequence;

[0043] S223. Construct a target function, and the theoretical attitude control matrix F​d Substituted into the objective function, the output target support force F is obtained when the objective function reaches the minimum value z , as follows:

[0044] Min W = (AF z '-F d ) T Q(AF z '-F d )+F z ' T RF z '

[0045] Meanwhile, AF z ' and F z ' satisfy the following constraints:

[0046] T min ≤AF z '≤T max

[0047] 0≤F z '≤F z,max

[0048] Wherein, W represents the objective function, T represents the transpose matrix, Q and R both represent the weight matrix, T min represents the lower limit of the output of the swing arm motor, T max represents the upper limit of the output of the swing arm motor, F z,max represents the upper limit of the support force, x1 and y1 represent the X-axis coordinate and Y-axis coordinate of the first swing arm end in the world coordinate system respectively, x2 and y2 represent the X-axis coordinate and Y-axis coordinate of the second swing arm end in the world coordinate system respectively, x3 and y3 represent the X-axis coordinate and Y-axis coordinate of the third swing arm end in the world coordinate system respectively, and x4 and y4 represent the X-axis coordinate and Y-axis coordinate of the fourth swing arm end in the world coordinate system respectively.

[0049] Further, the target acceleration of the center of mass in the Z-axis, and the target angular acceleration of the center of mass around the X-axis and the Y-axis are determined by the following method:

[0050] The actual moving speed V z of the center of mass in the Z-axis, the target height and the actual height H z , the target rotation angle of the center of mass around the X-axis, the actual angle φ x , the target angular velocity and the actual angular velocity of the center of mass around the Y-axis, and the target rotation angle of the center of mass around the Y-axis, the actual angle φ ytarget angular velocity of rotation and actual angular velocity The target acceleration of the center of mass on the Z axis and the target angular acceleration of the center of mass around the X axis and the Y axis are calculated based on the virtual model controller and according to the data converted to the world coordinate system, and the calculation formula is as follows:

[0051]

[0052]

[0053] wherein, represents the target acceleration of the center of mass on the Z axis, represents the target angular acceleration of the center of mass around the X axis, represents the target angular acceleration of the center of mass around the Y axis, k pz , k dz , k p,roll , k d,roll , k p,pitch and k d,roll all represent virtual model control parameters, and represent the target height and the actual height in the world coordinate system, respectively, represents the actual moving speed in the world coordinate system, and represent the target rotation angle, the actual angle and the actual angular velocity of the center of mass rotating around the X axis of the center of mass coordinate system in the world coordinate system, respectively, and represent the target rotation angle, the actual angle and the actual angular velocity of the center of mass rotating around the Y axis of the center of mass coordinate system in the world coordinate system, respectively.

[0054] Further, the target output torque of the hub motor is determined by the following formula:

[0055] τ ω = F ω r

[0056] wherein τ ω represents the target output torque of the hub motor, and r represents the wheel radius of the eight-degree-of-freedom wheel-legged robot.

[0057] Further, the target output torque of the swing arm motor is calculated by the following formula:

[0058] τ s = J T F z '

[0059] wherein τ sJ represents a Jacobian matrix of the four swing arms in the Z-axis direction, and T represents a transposed matrix.

[0060] The present application has the beneficial effects that: according to the target moving speed, the target rotation angle, the target rotation angular velocity and the target height, the target forward force for controlling the moving direction and the moving speed of the eight-degree-of-freedom wheel-legged robot and the target support force for controlling the posture are determined, and the target output torque of the wheel hub motor and the swing arm motor is determined according to the target forward force and the target support force, the vehicle body is controlled according to the target output torque, the movement according to the target moving direction, the target moving speed and the posture can be realized, and the vehicle body posture adaptive adjustment in a complex terrain environment can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0061] The present application will be further described below in combination with the drawings and embodiments:

[0062] Figure 1 The flowchart of the present application is shown in the figure;

[0063] Figure 2 The structure schematic diagram of the eight-degree-of-freedom wheel-legged robot in the embodiment is shown in the figure;

[0064] Figure 3 The center of mass coordinate system schematic diagram in the embodiment is shown in the figure;

[0065] Figure 4 The slope working condition simulation result of the embodiment is shown in the figure;

[0066] Figure 5 The single-side obstacle working condition simulation result of the embodiment is shown in the figure;

[0067] Figure 6 The double-side obstacle working condition simulation result of the embodiment is shown in the figure;

[0068] Figure 7 The impact disturbance working condition simulation result of the embodiment is shown in the figure;

[0069] Figure 8 The random terrain working condition simulation result of the embodiment is shown in the figure;

[0070] Figure 9 The posture tracking working condition simulation result of the embodiment is shown in the figure;

[0071] The figure shows the vehicle wheel, the wheel hub motor, the swing arm connecting rod, the swing arm motor, and the vehicle body. DETAILED DESCRIPTION

[0072] The present application will be further described below in combination with the drawings and embodiments:

[0073] The present application provides a control method of an eight-degree-of-freedom wheel-legged robot, which comprises the following steps:

[0074] S1. Obtain target control information of the eight-degree-of-freedom wheel-legged robot;

[0075] The target control information comprises a target moving speed, a target rotation angle, a target height, and a target rotation angular velocity;

[0076] S2. Determine a target advancing force according to the target moving speed and the target rotation angle;

[0077] Determine a target supporting force according to the target height, the target rotation angular velocity, and the target rotation angle;

[0078] S3. Determine a target output torque of a wheel hub motor of the eight-degree-of-freedom wheel-legged robot according to the target advancing force;

[0079] Determine a target output torque of a swing arm motor of the eight-degree-of-freedom wheel-legged robot according to the target supporting force;

[0080] S4. A controller in the eight-degree-of-freedom wheel-legged robot controls the wheel hub motor and the swing arm motor to output corresponding target output torques;

[0081] By the above method, the eight-degree-of-freedom wheel-legged robot can be controlled to move according to a target moving direction, a target moving speed, and a target posture, and posture self-adaptive adjustment in a complex terrain environment can be realized.

[0082] In the embodiment, the eight-degree-of-freedom wheel-legged robot comprises four wheel-legged structures, four swing arm motors 4, four wheel hub motors 2, a body 5, and a controller, as shown in Figure 2 ;

[0083] The wheel-legged structure comprises a swing arm connecting rod 3 and a wheel 1;

[0084] One end of the swing arm connecting rod 3 is fixedly connected with the center of the wheel 1, and the other end of the swing arm connecting rod 3 is connected with the power output end of the swing arm motor 4, for changing the posture of the eight-degree-of-freedom wheel-legged robot;

[0085] The wheel 1 is connected with the power output end of the wheel hub motor 2, for changing the moving direction and moving speed of the eight-degree-of-freedom wheel-legged robot;

[0086] The swing arm motor 4 and the wheel hub motor 2 are both fixedly arranged on the body 5 of the eight-degree-of-freedom wheel-legged robot and are in control connection with the controller; the swing arm motor 4 can be arranged at a position close to the center of mass of the robot, so as to reduce the moment of inertia of the robot;

[0087] The body 5 is provided with one wheel-legged structure around each of four sides, i.e., one wheel-legged structure is arranged on the front left, the front right, the back left, and the back right, respectively;

[0088] Common wheel-legged robots include wheel-legged robots using active suspension as leg structure and composite wheel-legged robots. Although the aforementioned wheel-legged robots have strong terrain adaptability, they have complex structure and need to consider switching between different modes, and their stability highly depends on complex control system. The eight-degree-of-freedom wheel-legged robot in the application uses swing arm linkage as leg, which not only has simple structure, but also can change the attitude of the body, and the way of changing the attitude of the body in the application is more flexible compared with common wheel-legged robots.

[0089] The attitude and inertial sensor is integrated in the body for real-time acquisition of attitude information of the robot under different road conditions. A magnetic encoder is also arranged at the end of the motor shaft for real-time monitoring of the rotation angle of the motor, and the angular velocity of the motor can be determined according to the rotation angle of the motor.

[0090] In the embodiment, before obtaining the target control information of the eight-degree-of-freedom wheel-legged robot, a center of mass coordinate system is established, and the establishment method is as follows:

[0091] A center of mass coordinate system is established with the center of mass of the eight-degree-of-freedom wheel-legged robot as the origin, as shown in Figure 3 The positive direction of the Z-axis of the center of mass coordinate system is perpendicular to the body plane of the eight-degree-of-freedom wheel-legged robot and points upward, the positive direction of the X-axis of the center of mass coordinate system is parallel to the body plane of the eight-degree-of-freedom wheel-legged robot and points forward, and the Y-axis of the center of mass coordinate system is determined by the right-hand rule. The aforementioned upward and forward directions are taken as reference directions. Figure 3

[0092] By establishing the coordinate system, a basis for subsequently intuitively describing the motion target and force state of the eight-degree-of-freedom wheel-legged robot (hereinafter referred to as robot) can be provided.

[0093] In the embodiment, in step S1, the target control information of the eight-degree-of-freedom wheel-legged robot is obtained.

[0094] The target control information includes target moving speed, target rotation angle, target height and target rotation angular velocity.

[0095] The target moving speed includes the target moving speed of the center of mass of the eight-degree-of-freedom wheel-legged robot on the X-axis

[0096] The target rotation angle includes the target rotation angle of the center of mass of the eight-degree-of-freedom wheel-legged robot around the X-axis the target rotation angle around the Y-axis and the target rotation angle around the Z-axis and correspond to roll angle, pitch angle and yaw angle respectively. ​

[0097] The target height refers to the target height of the center of mass of the eight-degree-of-freedom wheeled robot on the Z-axis. That is, the coordinates of the centroid on the Z-axis;

[0098] The target rotational angular velocity includes the target rotational angular velocity of the center of mass of the eight-DOF wheeled robot rotating around the X-axis. and the rotational angular velocity of the target rotating around the Y-axis

[0099] The purpose of acquiring the above target control information is to transform it into control information for controlling the robot's motion (i.e., the target output torque of the motor), thereby enabling the robot to move in the desired direction, speed, and posture.

[0100] In this embodiment, in step S2, the forward force of the target is determined based on the target's moving speed and the target's rotation angle;

[0101] Determine the target support force based on the target height, target rotation angular velocity, and target rotation angle;

[0102] The target forward force is obtained through the following steps:

[0103] S211. Based on the PD controller (proportional-derivative controller), according to the target moving speed of the centroid on the X-axis. Calculate the target traction force F x ;

[0104]

[0105] Where, k pv V represents the parameters of the PD controller. x This represents the actual velocity of the center of mass along the X-axis; the target traction force is used to control the robot's forward speed.

[0106] S212. Based on the PD controller, according to the target rotation angle around the Z-axis... Calculate the target torque T of the center of mass about the Z-axis z ;

[0107]

[0108] Where, k pw and k dw All represent parameters of the PD controller, φ z This represents the actual angle of rotation of the center of mass around the Z-axis. The actual angular velocity of the center of mass rotating about the Z-axis, and the target torque T of the center of mass about the Z-axis. z ;

[0109] When calculating the target torque, there is no need to convert the data to the world coordinate system, because the target torque is mainly used to control the differential steering of the robot, and the differential steering is realized by controlling the angular velocity of the robot, and the angular velocity of the robot is the angular velocity of the center of mass of the robot rotating around the Z axis, and the Z axis of the center of mass coordinate system and the Z axis of the world coordinate system point in the same direction, so when the robot is controlled to perform differential steering, that is, when the target torque is calculated, there is no need to convert the coordinate system.

[0110] S213. According to the target traction force F x and the target torque T of the center of mass around the Z axis z The target forward force is calculated according to the following formula:

[0111]

[0112] Wherein, F ω represents the target forward force, F ω1 , F ω2 , F ω3 and F ω4 correspond to the target forward force output by the first to fourth hub motors, respectively, W 2,1 , W 2,2 , W 2,3 and W 2,4 correspond to the Y direction distance from the rotation center of the first to fourth swing arm links to the center of mass, respectively.

[0113] The first hub motor refers to the hub motor on the left front of the eight-degree-of-freedom wheel-legged robot, and in counterclockwise order, the second hub motor, the third hub motor and the fourth hub motor are arranged in sequence, and the swing arm link is arranged in the same order as the hub motor.

[0114] Through the above method, the target force that different hub motors should output can be calculated, and the robot can be controlled to move according to the target forward direction and the target speed.

[0115] Further, the target support force is determined by the following method:

[0116] The principle of determining the target support force in the present application is to combine the center of mass posture and height with the virtual model control strategy and the center of mass quasi-static control strategy, to obtain the optimal target support force by solving a quadratic optimization problem, which avoids the problem of solving the inverse Jacobian matrix, and can also obtain the target support force that ensures the relative stillness of the center of mass, so that the robot moves more smoothly. The foregoing method is summarized as the following steps:

[0117] S221. According to the target height, determine the target acceleration of the center of mass on the Z axis According to the target rotational angular velocity and the target rotation angle, determine the target rotational angular acceleration of the center of mass around the X axis and target angular acceleration of the center of mass around the Y axis

[0118] the target acceleration of the center of mass along the Z axis, and the target angular acceleration of the center of mass around the X axis and the Y axis are determined by the following method:

[0119] the actual moving speed V of the center of mass along the Z axis z , target height and actual height H z , target rotation angle of the center of mass around the X axis actual angle φ x , target angular velocity and actual angular velocity , and target rotation angle of the center of mass around the Y axis actual angle φ y , target angular velocity and actual angular velocity are converted to the world coordinate system. The conversion of the coordinate system is usually achieved by calculating a rotation matrix of one coordinate system relative to another coordinate system. The process of calculating the rotation matrix is a prior art, which will not be described here. The coordinates in the center of mass coordinate system are multiplied by the rotation matrix of the center of mass coordinate system relative to the world coordinate system, so as to obtain the coordinates in the world coordinate system. Based on the virtual model controller and according to the data converted to the world coordinate system, the target acceleration of the center of mass along the Z axis, and the target angular acceleration of the center of mass around the X axis and the Y axis are calculated, and the calculation formula is as follows:

[0120]

[0121] wherein, represents the target acceleration of the center of mass along the Z axis, represents the target angular acceleration of the center of mass around the X axis, represents the target angular acceleration of the center of mass around the Y axis, k pz , k dz , k p,roll , k d,roll , k p,pitch and k d,roll all represent virtual model control parameters, and respectively represent the target height and the actual height in the world coordinate system, represents the actual moving speed in the world coordinate system, and respectively represent the target rotation angle, the actual angle and the actual angular velocity of the center of mass around the X axis of the center of mass coordinate system in the world coordinate system, and respectively represent the target rotation angle, actual angle and actual angular velocity of the center of mass rotating around the Y-axis of the center of mass coordinate system under the world coordinate system;

[0122] In the process of calculating the target support force, coordinate system conversion is needed. Because the world coordinate system can better describe the influence of the components of gravity in different directions on the robot, by converting the data under the center of mass coordinate system to the world coordinate system, the component of gravity in each direction can be accurately calculated according to the inclination angle of the terrain and the attitude of the robot, and then the additional torque required by each motor to maintain balance and achieve motion can be determined. Moreover, converting the data to the world coordinate system can more intuitively and accurately describe the state of the robot, and can also analyze various external forces acting on the robot under a unified framework. By combining the force state and the motion state of the robot, the torque required by each motor to overcome external forces can be more accurately calculated;

[0123] S222. According to the target acceleration Target rotation angle acceleration And Determine the theoretical attitude control matrix F d The theoretical attitude control matrix is as follows:

[0124]

[0125] Wherein, F z represents the theoretical support force, F z1 , F z2 , F z3 and F z4 respectively represent the theoretical support force output by the first swing arm motor to the fourth swing arm motor, T x represents the target torque of the center of mass around the X-axis, T y represents the target torque of the center of mass around the Y-axis, m represents the mass of the eight-degree-of-freedom wheel-legged robot, I G represents the equivalent moment of inertia of the center of mass, and g represents the acceleration of gravity.

[0126] The first swing arm motor refers to the swing arm motor in front of the left side of the eight-degree-of-freedom wheel-legged robot, and in counterclockwise order, the second swing arm motor, the third swing arm motor and the fourth swing arm motor are sequentially arranged;

[0127] S223. Construct the objective function, and substitute the theoretical attitude control matrix F d into the objective function. When the objective function reaches the minimum value, the target support force F z ' is output, and the formula is as follows:

[0128] Min W = (AF z '-F d ) T Q(AFz '-F d )+F z ' T RF z '

[0129] Meanwhile, AF z 'and F z 'satisfy the following constraints:

[0130] T min ≤AF z '≤T max

[0131] 0≤F z '≤F z,max

[0132] Wherein, W represents the objective function, T represents the transpose matrix, Q and R both represent the weight matrix, T min represents the lower limit of the swing arm motor output, T max represents the upper limit of the swing arm motor output, F z,max represents the upper limit of the support force, x1 and y1 represent the X-axis coordinate and Y-axis coordinate of the first swing arm end in the world coordinate system respectively, x2 and y2 represent the X-axis coordinate and Y-axis coordinate of the second swing arm end in the world coordinate system respectively, x3 and y3 represent the X-axis coordinate and Y-axis coordinate of the third swing arm end in the world coordinate system respectively, x4 and y4 represent the X-axis coordinate and Y-axis coordinate of the fourth swing arm end in the world coordinate system respectively, the conversion of the coordinate system is the prior art, which is not described here;

[0133] The above steps calculate a reference support force, i.e. the theoretical support force in the application, through the virtual model controller. The theoretical support force is only the optimal support force for achieving the target attitude, but it is not the optimal support force that the robot can output. Under the premise of ensuring that the robot center of mass is relatively stationary, an optimization problem is constructed through the center of mass quasi-static control method, i.e. within the output range of the robot, the optimal support force that can actually be output is determined through the objective function, i.e. the target support force. Through the above method, the problem of solving the inverse Jacobian matrix can be avoided, and the body attitude can be as stable as possible.

[0134] In this embodiment, in step S3, the target output torque of the hub motor of the eight-degree-of-freedom wheel-legged robot is determined according to the target forward force;

[0135] The target output torque of the swing arm motor of the eight-degree-of-freedom wheel-legged robot is determined according to the target support force;

[0136] The target output torque of the hub motor is determined by the following formula:

[0137] τ ω=F ω r

[0138] wherein, τ ω represents the target output torque of the hub motor, and r represents the wheel radius of the eight-degree-of-freedom wheel-legged robot;

[0139] The target output torque of the swing arm motor is calculated by the following formula:

[0140] τ s = J T F z '

[0141] wherein, τ s represents the target output torque of the swing arm motor, J represents the Jacobian matrix of the four swing arms in the Z-axis direction, and T represents the transpose matrix;

[0142] The calculation process of the Jacobian matrix is prior art, which is not described here;

[0143] The above method converts the target forward force and the target support force into the output torque of the hub motor and the swing arm motor, respectively, which can output the corresponding force by controlling the output torque of the motor, and then control the robot.

[0144] In this embodiment, in step S4, the controller in the eight-degree-of-freedom wheel-legged robot controls the hub motor and the swing arm motor to output the corresponding target output torque; the foregoing method can realize the target moving speed, the target rotation angle, the target height and the target rotation angular velocity within the output range of the robot.

[0145] In order to verify the feasibility of the proposed control method and structural design, a variety of working conditions of the eight-degree-of-freedom wheel-legged robot were simulated in the Webots simulation environment, and joint virtual model control was used as a control group, which means that the wheel legs of the robot were controlled by virtual model control (VMC). The virtual model control for controlling the robot is prior art, which is not described here. The various working conditions include slope working condition, unstructured terrain working condition and attitude tracking working condition, etc. In the simulation, the mass and size parameters of the robot are strictly set according to the data in Table 1 to ensure the accuracy of the simulation results and the comparability with the actual application. Table 1 is as follows:

[0146]

[0147] Table 1 Model parameters of the eight-degree-of-freedom wheel-legged robot

[0148] In the experiment, the control frequency is set to 0.5 kHz to ensure the response speed of real-time control. The range, resolution, and noise of the sensor are set within a reasonable range to approach the actual application environment. At the same time, the key parameters such as torque and speed of the motor are consistent with the actual motor, so as to ensure that the simulation data has good authenticity and reference value. These settings provide a reliable experimental basis for verifying the effectiveness of the control strategy and the rationality of the structure design.

[0149] Slope working condition experiment: In the simulation environment, 14° slope and single bridge slope working condition experiment scene with a height of 80mm are respectively built, and the joint virtual model control and the control method of the application of the eight-degree-of-freedom wheel-legged robot in this working condition are compared and simulated. The k p of the joint virtual model is set to 3.5, and the k d is set to 0.5; based on the height of the single bridge and the distance between the wheels of the robot, it can be calculated that when the eight-degree-of-freedom wheel-legged robot passes through the single bridge, a roll angle of about 11.4° will be generated. As shown in Figure 4 (a), in the 14° slope working condition, the control method of the application can more effectively keep the body posture stable and quickly adjust the pitch angle from-14° to-0.25° than the joint virtual model control; as shown in Figure 4 (b), in the single bridge working condition, the control method of the application can quickly adjust the roll angle from-11.8° to-0.43° and keep it stable compared with the joint virtual model control; this experiment proves that the control method of the application can effectively avoid the problem of overturning or losing balance caused by excessive inclination of the posture, and significantly improves the environmental adaptability and posture stability of the robot.

[0150] Non-structured terrain working condition experiment: In the simulation environment, a non-structured terrain working condition experiment scene is built, and single obstacle working condition, double obstacle working condition, impact disturbance working condition and random road working condition simulation experiments are carried out. The experimental group adopts the control method of the application, and the control method of the joint virtual model is used in the control group. The k p of the joint virtual model control parameter is set to 3.5, and the k d is set to 0.5; in the simulation, the obstacle height of the single obstacle working condition and the double obstacle working condition is 50mm; in the impact disturbance working condition, the vertical impact force is 5.79kg.m / s, the lateral and longitudinal impact force is 3.43kg·m / s, and the fluctuation amplitude of the random road working condition terrain is 0-0.13m.

[0151] Figure 5(a) and (b) show the relevant data of the eight-degree-of-freedom wheel-legged robot in the single-side obstacle working condition. As can be seen from the changes in the attitude angles, the control method of the application can effectively suppress the disturbance response of the robot in the roll angle and the pitch angle when passing through the single-side obstacle compared with the joint virtual model control method, wherein the roll angle fluctuation is reduced from a maximum of 4.1° to 0.07°, and the pitch angle fluctuation is reduced from a maximum of 3.9° to 0.1°, and the vehicle body attitude quickly returns to the equilibrium state. In contrast, the wheel-legged mobile robot controlled by the joint virtual model control method has obvious roll angle and pitch angle fluctuations, and the stability is poor.

[0152] Figure 6 (a) and (b) show the relevant data of the eight-degree-of-freedom wheel-legged robot in the double-side obstacle working condition. As can be seen from the changes in the attitude angles, the control method of the application can more effectively suppress the disturbance response of the mobile robot in the pitch angle when passing through the double-side obstacle compared with the joint virtual model control method, wherein the pitch angle fluctuation is reduced from a maximum of 8.1° to -0.65°, ensuring that the vehicle body attitude quickly returns to the equilibrium state, while the robot controlled by the joint virtual model control method has obvious pitch angle fluctuations, and the stability is poor.

[0153] Figure 7 (a), (b) and (c) show the relevant data of the eight-degree-of-freedom wheel-legged robot in a series of experimental scenarios of impact and recovery to stability on the vertical plane, the lateral plane and the longitudinal plane of the vehicle body. The impact force on the vertical plane is 5.79 kg·m / s, and the impact forces on the lateral plane and the longitudinal plane are 3.43 kg·m / s. As can be seen from the changes in the attitude angles, when subjected to external impact, the robot can quickly realize attitude adjustment and recover to balance under the control method of the application compared with the joint virtual model control, and the anti-impact dynamic stability is better.

[0154] Figure 8 (a) and (b) show the relevant data of the eight-degree-of-freedom wheel-legged robot in the random road working condition. As can be seen from the changes in the attitude angles, the control method of the application can effectively suppress the disturbance response of the robot in the pitch angle and the roll angle when passing through the random road working condition compared with the joint virtual model control, wherein the pitch angle fluctuation is reduced from a maximum of -6.8° to 0.7°, and the roll angle fluctuation is reduced from a maximum of -8.7° to 0.5°, ensuring that the vehicle body attitude quickly returns to the equilibrium state.

[0155] Attitude tracking working condition experiment: under the control method of the application, attitude angle tracking experiments of roll angle sine signal tracking, pitch angle sine signal tracking and fusion of roll angle and pitch angle are carried out respectively, and the sine amplitude is 5.73°. In the simulation experiment process, the actual vehicle body attitude angle is measured by the IMU added by the simulation environment. Figure 9As shown, the average error at the peak and valley of the sine wave is 0.03° in the roll angle tracking mode; the average error at the peak and valley of the sine wave is about 0.01° in the pitch angle tracking mode; the comprehensive average error is 0.02° when the roll angle tracking and the pitch angle tracking are performed simultaneously, which proves that the control strategy has good dynamic response performance and can effectively follow the expected trajectory.

[0156] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the purpose and scope of the technical solutions of the present application, and they should all be covered in the scope of the claims of the present application.

Claims

1. A control method of an eight-degree-of-freedom wheel-legged robot, characterized by: The method comprises the following steps: S1. Obtain target control information of an eight-degree-of-freedom wheel-legged robot; The target control information comprises a target moving speed, a target rotation angle, a target height, and a target rotation angular velocity; S2. Determine a target forward force according to the target moving speed and the target rotation angle; Determine a target support force according to the target height, the target rotation angular velocity, and the target rotation angle; S3. Determine a target output torque of a hub motor of the eight-degree-of-freedom wheel-legged robot according to the target forward force; Determine a target output torque of a swing arm motor of the eight-degree-of-freedom wheel-legged robot according to the target support force; S4. A controller in the eight-degree-of-freedom wheel-legged robot controls the hub motor and the swing arm motor to output corresponding target output torques; wherein: The eight-degree-of-freedom wheel-legged robot comprises four wheel-legged structures, four swing arm motors, four hub motors, a body, and a controller; The wheel-legged structure comprises a swing arm connecting rod and a wheel; One end of the swing arm connecting rod is fixedly connected with the center of the wheel, and the other end of the swing arm connecting rod is connected with the power output end of the swing arm motor, for changing the posture of the eight-degree-of-freedom wheel-legged robot; The wheel is connected with the power output end of the hub motor, for changing the moving direction and speed of the eight-degree-of-freedom wheel-legged robot; The swing arm motor and the hub motor are both fixedly arranged on the body of the eight-degree-of-freedom wheel-legged robot and are in control connection with the controller; One wheel-legged structure is arranged around the body of the eight-degree-of-freedom wheel-legged robot; Before obtaining the target control information of the eight-degree-of-freedom wheel-legged robot, a center of mass coordinate system is established, and the establishment method is as follows: A center of mass coordinate system is established with the center of mass of the eight-degree-of-freedom wheel-legged robot as the origin, the positive direction of the Z-axis of the center of mass coordinate system is perpendicular to the body plane of the eight-degree-of-freedom wheel-legged robot and points upward, the positive direction of the X-axis of the center of mass coordinate system is parallel to the body plane of the eight-degree-of-freedom wheel-legged robot and points forward, and the Y-axis is determined by the right-hand rule; The target moving speed includes a target moving speed of a center of mass of the eight-degree-of-freedom wheel-legged robot on the X axis The target rotation angle includes a target rotation angle of a center of mass of the eight-degree-of-freedom wheel-legged robot rotating around an X axis a target rotation angle of rotating around a Y axis and a target rotation angle of rotating around a Z axis The target height refers to the target height of the center of mass of the eight-degree-of-freedom wheel-legged robot on the Z axis The target rotation angular velocity includes a target rotation angular velocity of a center of mass of the eight-degree-of-freedom wheel-legged robot rotating around an X axis and a target rotation angular velocity rotating around a Y axis The target forward force is obtained by the following steps: S211. Based on the PD controller, the target moving speed of the center of mass on the X axis is calculated according to the target moving speed of the center of mass on the X axis The target traction force F is calculated x ; where k pv represents a parameter of the PD controller, V x represents the actual velocity of the centroid in the X-axis direction; S212. Based on the PD controller, the target rotation angle of rotation around the Z axis is calculated according to the target rotation angle of rotation around the Z axis The target torque T around the Z axis is calculated z ; where k pw and k dw are parameters of the PD controller, φ z is the actual angle of rotation of the center of mass around the Z axis, is the actual angular velocity of rotation of the center of mass around the Z axis; S213. The target tractive force F x and the target torque T of the center of mass around the Z axis z The target forward force is calculated according to the following formula: wherein F ω represents a target forward force, F ω1 , F ω2 , F ω3 , and F ω4 correspond to target forward forces output by the first to fourth in-wheel motors, respectively, W 2,1 , W 2,2 , W 2,3 , and W 2,4 correspond to Y-direction distances from the rotation centers of the first to fourth swing arm links to the center of mass, respectively. The first hub motor refers to the hub motor at the left front of the eight-degree-of-freedom wheel-legged robot, and the second hub motor, the third hub motor, and the fourth hub motor are sequentially arranged in counterclockwise order, and the swing arm connecting rod is arranged in the same order as the hub motor; The target support force is determined by the following method: S221. Determine target acceleration of the center of mass on the Z axis according to the target height Determine target angular acceleration of the center of mass about the X axis according to the target angular velocity and the target angle of rotation and target angular acceleration of the center of mass about the Y axis S222. The target acceleration Target rotational angular acceleration and Determining a theoretical attitude control matrix F d , the theoretical attitude control matrix being as follows: where F z represents the theoretical support force, F z1 , F z2 , F z3 , and F z4 represent the theoretical support forces of the first swing arm motor to the fourth swing arm motor, respectively, T x represents the target torque of the mass center around the X axis, T y represents the target torque of the mass center around the Y axis, m represents the mass of the eight-degree-of-freedom wheel-legged robot body, I G represents the equivalent moment of inertia of the mass center, and g represents the acceleration of gravity; The first swing arm motor refers to the swing arm motor at the left front of the eight-degree-of-freedom wheel-legged robot, and the second swing arm motor, the third swing arm motor, and the fourth swing arm motor are sequentially arranged in counterclockwise order; S223. Constructing the objective function, the theoretical attitude control matrix F d Substituting into the objective function, the target support force F is output when the objective function is minimized z , as follows: Min W = (AF z '-F d ) T Q(AF z '-F d )+F z ' T RF z ' At the same time, AF z ' and F z ' satisfy the following constraints: T min ≤AF z '≤T max 0 < F z 0 < F z,max wherein W represents a target function, T represents a transpose matrix, Q and R both represent weight matrices, T min represents a lower limit of the swing arm motor output, T max represents an upper limit of the swing arm motor output, F z,max represents an upper limit of the support force, x1 and y1 represent the X-axis coordinate and Y-axis coordinate of the first swing arm end in the world coordinate system, respectively, x2 and y2 represent the X-axis coordinate and Y-axis coordinate of the second swing arm end in the world coordinate system, respectively, x3 and y3 represent the X-axis coordinate and Y-axis coordinate of the third swing arm end in the world coordinate system, respectively, and x4 and y4 represent the X-axis coordinate and Y-axis coordinate of the fourth swing arm end in the world coordinate system, respectively.

2. The control method of the eight-degree-of-freedom wheel-legged robot according to claim 1, characterized by: The target acceleration of the center of mass on the Z-axis and the target rotation angular acceleration of the center of mass around the X-axis and the Y-axis are determined by the following method: actual movement speed V of the center of mass on the Z axis z , target height and actual height H z , target rotation angle of the center of mass around the X axis actual angle φ x , target rotation angular velocity and actual angular velocity and target rotation angle of the center of mass around the Y axis actual angle φ y , target rotation angular velocity and actual angular velocity In the world coordinate system, the target acceleration of the center of mass on the Z axis and the target rotation angular acceleration of the center of mass around the X axis and the Y axis are calculated based on the virtual model controller and according to the data converted to the world coordinate system, and the calculation formula is as follows: wherein represents the target acceleration of the center of mass in the Z axis, represents the target angular acceleration of the center of mass in the X axis, represents the target angular acceleration of the center of mass in the Y axis, pz , k dz , k p,roll , k d,roll , k p,pitch and k d,roll all represent virtual model control parameters, and respectively represent the target height and the actual height in the world coordinate system, represents the actual moving speed in the world coordinate system, and respectively represent the target rotation angle, the actual angle and the actual angular velocity of the center of mass rotating around the X axis of the center of mass coordinate system in the world coordinate system, and respectively represent the target rotation angle, the actual angle and the actual angular velocity of the center of mass rotating around the Y axis of the center of mass coordinate system in the world coordinate system.

3. The control method of the eight-degree-of-freedom wheel-legged robot according to claim 1, characterized by: The target output torque of the hub motor is determined by the following formula: τ ω = F ω r where τ ω represents the target output torque of the wheel motor, and r represents the wheel radius of the eight-degree-of-freedom wheel-legged robot.

4. The control method of the eight-degree-of-freedom wheel-legged robot according to claim 2, characterized by: The target output torque of the swing arm motor is calculated by the following formula: tau s = J T F z ' where τ s represents the target output torque of the swing arm motor, J represents the Jacobian matrix of the four swing arms in the Z-axis direction, and T represents the transpose matrix.

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