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

Abstract

The invention provides a control method of an eight-degree-of-freedom wheel-legged robot. The control method comprises the following steps: S1, acquiring 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 speed; s2, determining a target forward force according to the target moving speed and the target rotating angle; determining a target supporting force according to the target height, the target rotation angular velocity and the target rotation angle; s3, the target output torque of a hub motor of the eight-degree-of-freedom wheel-legged robot is determined 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 a hub motor and a swing arm motor to output corresponding target output torque; through the control method, the robot can be controlled to move according to the target advancing direction, the target speed and the target posture.

Description

Technical Field

[0001] The present invention relates to the field of artificial intelligence, and in particular to a control method for an eight-degree-of-freedom wheel-legged robot. Background Art

[0002] A wheel-legged robot is a robot that combines the advantages of wheeled mobility and leg support. It has strong obstacle-crossing ability and stability. This type of robot is widely used in industrial automation, rescue missions, disaster response, and home services.

[0003] Most wheel-legged robots are mainly driven by wheels on flat terrain. They adjust their posture by actuating the leg joints to maintain stability and minimize the wheel leaving the ground, thereby improving driving speed and stability. The control of the robot's posture is a key issue. Most current studies have proposed their own control methods for different structural features. For example, two-wheeled legged robots are mostly under-actuated designs with relatively simple structures. They mainly rely on the coordination between wheels and legs and the flexibility of joints to achieve balance adjustment. A control model based on a linear quadratic regulator is usually used to ensure stability. However, due to the under-actuated characteristics, this structure has high requirements for balance and posture control, and its adaptability to complex terrain is relatively limited. Four-wheeled legged robots usually have a tandem leg structure with a large range of joint motion. When all wheels are on the ground, there is no need for dynamic balance. Therefore, the focus of attitude control is to accurately track the body attitude. Although this tandem structure has good movement flexibility and rapid adjustment capabilities, existing four-wheeled legged robots are mostly focused on smooth terrain control, with weak adaptability on complex terrain, and the accuracy and stability of dynamic attitude adjustment still need to be improved. In addition, some wheeled legged robots rely on complex mechanical structures and sensor systems, making it difficult to achieve lightweight design. At the same time, the high dependence on computing resources also affects the real-time and stability of the system.

[0004] Therefore, in order to solve the above technical problems, it is urgent to propose a new technical means. Summary of the invention

[0005] In view of this, in order to improve the traversal capability and posture balance control capability of the wheel-legged robot on complex terrain, the present invention proposes a control method for an eight-degree-of-freedom wheel-legged robot.

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

[0007] S1. Obtaining target control information of the eight-degree-of-freedom wheel-legged robot;

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

[0009] S2. Determine the target forward force according to the target moving speed and the target rotation angle;

[0010] determining a target support force according to a target height, a target rotation angular velocity, and a target rotation angle;

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

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

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

[0014] Furthermore, the eight-degree-of-freedom wheel-leg robot includes four wheel-leg structures, four swing arm motors, four wheel hub motors, a fuselage and a controller;

[0015] The wheel-leg structure includes a swing arm connecting rod and a wheel;

[0016] One end of the swing arm connecting rod is fixedly connected to the center of the wheel, and the other end of the swing arm connecting rod is connected to the power output end of the swing arm motor, so as to change the posture of the eight-degree-of-freedom wheel-legged robot;

[0017] The wheel is connected to the power output end of the wheel hub motor and is used to change the travel direction and travel 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 control-connected to the controller;

[0019] A wheel-leg structure is correspondingly arranged on each of the four sides of the fuselage.

[0020] Furthermore, before obtaining the target control information of the eight-degree-of-freedom wheel-legged robot, it also includes establishing a center of mass coordinate system, 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. The Y axis of the center of mass coordinate system is determined by the right-hand rule.

[0022] Furthermore, 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.

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

[0024] 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.

[0025] The target rotational angular velocity includes the target rotational angular velocity of the center of mass of the eight-degree-of-freedom wheel-legged robot rotating around the X-axis and the target rotation angular velocity 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] Among them, k pv Represents the parameters of the PD controller, V x Indicates the actual velocity of the center of mass in the X-axis direction;

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

[0031]

[0032] Among them, k pw and k dw Both represent the parameters of the PD controller, φ z Indicates the actual angle of rotation of the center of mass around the Z axis, Indicates 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 of the center of mass around the Z axis z Calculate the target forward force using the following formula:

[0034]

[0035] Among them, F ω Indicates the target forward force, F ω1 、Fω2 、F ω3 and F ω4 Corresponding to the target forward force output by the first to fourth wheel hub motors, W 2,1 , W 2,2 , W 2,3 and W 2,4 They correspond to the Y-direction distances from the rotation centers of the first to fourth swing arm links to the center of mass;

[0036] The first hub motor refers to the hub motor on the left front of the eight-degree-of-freedom wheel-legged robot. In counterclockwise order, they are the second hub motor, the third hub motor and the fourth hub motor. The setting order of the swing arm connecting rod is consistent with the setting order of the hub motor.

[0037] Furthermore, 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 rotation angular acceleration of the center of mass around the X-axis based on the target rotation angular velocity and the target rotation angle and the target rotation angular acceleration on the Y axis

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

[0040]

[0041] Among them, F z Indicates the theoretical support force, F z1 、F z2 、F z3 and F z4 Respectively represent the theoretical support force output by the motors of the first to fourth swing arms, 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 body mass of the eight-degree-of-freedom wheel-legged robot, and I G represents the equivalent moment of inertia of the center of mass, and g represents the acceleration due to gravity;

[0042] The first swing arm motor refers to the swing arm motor on the left front of the 8-DOF wheel-legged robot. In counterclockwise order, the motors are the second swing arm motor, the third swing arm motor, and the fourth swing arm motor.

[0043] S223. Construct the objective function and transform the theoretical attitude control matrix Fd Substitute into the objective function, and when the objective function reaches the minimum value, output the target support force F z ', the formula is as follows:

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

[0045] At the same time, AF z ' and F z 'Satisfy the following constraints:

[0046] T min ≤AF z '≤T max

[0047] 0≤F z '≤F z,max

[0048] Among them, W represents the objective function, T represents the transposed matrix, Q and R both represent the weight matrix, and T min Indicates the lower limit of the swing arm motor output, T max Indicates the output upper limit of the swing arm motor, F z,max Indicates the upper limit of the support force, x 1 and 1 They represent the X-axis coordinate and Y-axis coordinate of the end of the first swing arm in the world coordinate system, respectively. 2 and 2 They represent the X-axis coordinate and Y-axis coordinate of the second swing arm end in the world coordinate system, respectively. 3 and 3 They represent the X-axis coordinate and Y-axis coordinate of the end of the third swing arm in the world coordinate system, respectively. 4 and 4 They respectively represent the X-axis coordinate and Y-axis coordinate of the end of the fourth swing arm in the world coordinate system.

[0049] Further, the target acceleration of the center of mass on the Z axis and the target rotational 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 of the center of mass on the Z axis z , Target height and the actual height H z , the target rotation angle of the center of mass around the X axis Actual angle φ x, target rotation angular velocity and the actual angular velocity And the target rotation angle of the center of mass around the Y axis Actual angle φ y , target rotation angular velocity and the actual angular velocity After conversion to 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 the data converted to the world coordinate system. The calculation formula is as follows:

[0051]

[0052]

[0053] in, represents the target acceleration of the center of mass on the Z axis, Indicates the target rotation angular acceleration of the center of mass around the X axis, Indicates the target rotation 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 actual height in the world coordinate system, Indicates the actual moving speed in the world coordinate system. and They represent the target rotation angle, actual angle, and 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 They 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 in the world coordinate system.

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

[0055] τ ω =F ω r

[0056] Among them, 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] Furthermore, the target output torque of the swing arm motor is calculated by the following formula:

[0058] τ s =JT F z '

[0059] Among them, τ s It 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 transposed matrix.

[0060] Beneficial effects of the present invention: The present invention determines the target forward force for controlling the moving direction and moving speed of the eight-degree-of-freedom wheel-legged robot, as well as the target supporting force for controlling the posture according to the target moving speed, target rotation angle, target rotation angular velocity and target height, and determines the target output torque of the hub motor and the swing arm motor according to the target forward force and the target supporting force, and controls the vehicle body according to the target output torque, which can achieve movement according to the target moving direction, moving speed and posture, thereby achieving adaptive adjustment of the vehicle body posture in complex terrain environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0062] Figure 1 It is a flow chart of the present invention;

[0063] Figure 2 This is a schematic diagram of the structure of an eight-degree-of-freedom wheel-legged robot in this embodiment;

[0064] Figure 3 Schematic diagram of the centroid coordinate system in this embodiment;

[0065] Figure 4 is the slope working condition simulation result of this embodiment;

[0066] Figure 5 This is the simulation result of the single-side obstacle working condition of this embodiment;

[0067] Figure 6 This is the simulation result of the double-sided obstacle working condition of this embodiment;

[0068] Figure 7 The simulation result of the impact disturbance working condition of this embodiment;

[0069] Figure 8 This is the simulation result of the random terrain working condition of this embodiment;

[0070] Fig. 9 The simulation result of the posture tracking condition of this embodiment;

[0071] Figure numerals: 1-wheel, 2-hub motor, 3-swing arm connecting rod, 4-swing arm motor, 5-fuselage. DETAILED DESCRIPTION

[0072] The present invention is further described below in conjunction with the accompanying drawings:

[0073] The present invention provides a control method for an eight-degree-of-freedom wheel-legged robot, comprising the following steps:

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

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

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

[0077] determining a target support force according to a target height, a target rotation angular velocity, and a target rotation angle;

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

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

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

[0081] Through the above method, the eight-degree-of-freedom wheel-legged robot can be controlled to move according to the target moving direction, target moving speed and target posture, thereby realizing adaptive posture adjustment in complex terrain environments.

[0082] In this embodiment, the eight-degree-of-freedom wheel-legged robot includes four wheel-leg structures, four swing arm motors 4, four wheel hub motors 2, a body 5 and a controller. Figure 2 As shown;

[0083] The wheel-leg 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 to the center of the wheel 1, and the other end of the swing arm connecting rod 3 is connected to the power output end of the swing arm motor 4, so as to change the posture of the eight-degree-of-freedom wheel-legged robot;

[0085] The wheel 1 is connected to the power output end of the wheel hub motor 2 to change the travel direction and travel 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 control-connected to the controller; the swing arm motor 4 can be arranged at a position close to the center of mass of the robot, which can reduce the rotational inertia of the robot;

[0087] The fuselage 5 is provided with a wheel-leg structure on each side thereof, that is, a wheel-leg structure is provided on the left front, right front, left rear and right rear respectively;

[0088] Common wheel-legged robots include wheel-legged robots that use active suspension as leg structures and composite wheel-legged robots. Although the aforementioned wheel-legged robots have strong terrain adaptability, they are complex in structure, and some of them also need to consider switching between different modes. Their stability is highly dependent on complex control systems. The eight-degree-of-freedom wheel-legged robot in this application uses swing arm connecting rods as legs, which is not only simple in structure, but also capable of changing the body posture. The method of changing the body posture in this application is more flexible than that of common wheel-legged robots.

[0089] The robot body is integrated with attitude and inertial sensors to obtain the robot's attitude information under different road conditions in real time. A magnetic encoder is also provided at the end of the motor shaft to monitor the motor's rotation angle in real time. The motor's angular velocity can be determined based on the motor's rotation angle.

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

[0091] Take the center of mass of the eight-degree-of-freedom wheel-legged robot as the origin and establish the center of mass coordinate system, such as Figure 3 As shown, the positive direction of the Z axis of the mass center coordinate system is perpendicular to the plane of the eight-degree-of-freedom wheel-legged robot and points upward, the positive direction of the X axis of the mass center coordinate system is parallel to the plane of the eight-degree-of-freedom wheel-legged robot and points forward, and the Y axis of the mass center coordinate system is determined by the right-hand rule. The above and the front are both Figure 3 The directions shown are reference directions;

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

[0093] In this embodiment, in step S1, 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 speed;

[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 rotating around the X-axis The target rotation angle around the Y axis and the target rotation angle around the Z axis and They 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 wheel-legged robot on the Z axis. That is the coordinate value of the center of mass on the Z axis;

[0098] The target rotational angular velocity includes the target rotational angular velocity of the center of mass of the eight-degree-of-freedom wheel-legged robot rotating around the X-axis and the target rotation angular velocity around the Y axis

[0099] The above target control information is obtained in order to be converted into control information for controlling the movement of the robot (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 target forward force is determined according to the target moving speed and the target rotation angle;

[0101] determining a target support force according to a target height, a target rotation angular velocity, and a target rotation angle;

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

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

[0104]

[0105] Among them, k pv Represents the parameters of the PD controller, V x Indicates the actual speed of the center of mass in the X-axis direction; the target traction force is used to control the forward speed of the robot;

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

[0107]

[0108] Among them, k pw and k dw Both represent the parameters of the PD controller, φ z Indicates the actual angle of rotation of the center of mass around the Z axis, Indicates the actual angular velocity of the center of mass rotating around the Z axis, and the target torque T of the center of mass rotating around 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 calculation of the target torque is mainly to control the robot to perform differential steering. Differential steering is achieved by controlling the angular velocity of the robot. The angular velocity of the robot is the angular velocity of the robot's center of mass rotating around the Z axis, and the Z axis of the center of mass coordinate system points in the same direction as the Z axis of the world coordinate system. Therefore, when performing differential steering control on the robot, that is, calculating the target torque, there is no need to perform coordinate system conversion;

[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 Calculate the target forward force using the following formula:

[0111]

[0112] Among them, F ω Indicates the target forward force, F ω1 、F ω2 、F ω3 and F ω4 Corresponding to the target forward force output by the first to fourth wheel hub motors, W 2,1 , W 2,2 , W 2,3 and W 2,4 They correspond to the Y-direction distances from the rotation centers of the first to fourth swing arm links to the center of mass;

[0113] The first wheel hub motor refers to the wheel hub motor on the left front of the 8-DOF wheel-legged robot. In counterclockwise order, the second wheel hub motor, the third wheel hub motor and the fourth wheel hub motor are in turn. The setting order of the swing arm connecting rod is consistent with that of the wheel hub motor.

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

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

[0116] The principle of determining the target support force in this 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, and obtain the optimal target support force by solving the quadratic optimization problem. This method avoids the problem of solving the Jacobian inverse matrix, and can also obtain the target support force that ensures the center of mass is relatively stationary, making the robot move more smoothly. The above method is summarized as the following steps:

[0117] S221. Determine the target acceleration of the center of mass on the Z axis according to the target height Determine the target rotation angular acceleration of the center of mass around the X-axis based on the target rotation angular velocity and the target rotation angle and the target rotation angular acceleration on the Y axis

[0118] The target acceleration of the center of mass on the Z axis and the target rotational 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 on the Z axis z , Target height and the actual height H z , the target rotation angle of the center of mass around the X axis Actual angle φ x , target rotation angular velocity and the actual angular velocity And the target rotation angle of the center of mass around the Y axis Actual angle φ y , target rotation angular velocity and the actual angular velocity The conversion to the world coordinate system is usually achieved by calculating the rotation matrix of one coordinate system relative to another coordinate system. The process of calculating the rotation matrix is ​​a prior art and will not be described here. The coordinates in the world coordinate system can be obtained by multiplying the coordinates in the center of mass coordinate system with the rotation matrix of the center of mass coordinate system relative to the world coordinate system. Based on the virtual model controller and the data converted to 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. The calculation formula is as follows:

[0120]

[0121] in, represents the target acceleration of the center of mass on the Z axis, Indicates the target rotation angular acceleration of the center of mass around the X axis, Indicates the target rotation 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 actual height in the world coordinate system, Indicates the actual moving speed in the world coordinate system. and They represent the target rotation angle, actual angle, and 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 They 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 in the world coordinate system respectively;

[0122] Coordinate system conversion is required in the process of calculating the target support force, 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 in the center of mass coordinate system to the world coordinate system, the components of gravity in various directions can be accurately calculated according to the inclination angle of the terrain and the posture of the robot, and then the additional torque that each motor needs to output to maintain balance and achieve movement can be determined; and by converting the data to the world coordinate system, the state of the robot can be described more intuitively and accurately, and the various external forces on the robot can be analyzed in a unified framework; by combining the force state and the motion state of the robot, the torque required to be output by each motor to overcome the external force can be more accurately calculated;

[0123] S222. According to the target acceleration Target rotation angular acceleration and Determine the theoretical attitude control matrix F d , the theoretical attitude control matrix is ​​as follows:

[0124]

[0125] Among them, F z Indicates the theoretical support force, F z1 、F z2 、F z3 and F z4 Respectively represent the theoretical support force output by the motors of the first to fourth swing arms, 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 body mass of the eight-degree-of-freedom wheel-legged robot, and I G represents the equivalent moment of inertia of the center of mass, and g represents the acceleration due to gravity;

[0126] The first swing arm motor refers to the swing arm motor on the left front of the 8-DOF wheel-legged robot. In counterclockwise order, the motors are the second swing arm motor, the third swing arm motor, and the fourth swing arm motor.

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

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

[0129] At the same time, AF z ' and F z 'Satisfy the following constraints:

[0130] T min ≤AF z '≤T max

[0131] 0≤F z '≤F z,max

[0132] Among them, W represents the objective function, T represents the transposed matrix, Q and R both represent the weight matrix, and T min Indicates the lower limit of the swing arm motor output, T max Indicates the output upper limit of the swing arm motor, F z,max Indicates the upper limit of the support force, x 1 and 1 They represent the X-axis coordinate and Y-axis coordinate of the end of the first swing arm in the world coordinate system, respectively. 2 and 2 They represent the X-axis coordinate and Y-axis coordinate of the second swing arm end in the world coordinate system, respectively. 3 and 3 They represent the X-axis coordinate and Y-axis coordinate of the end of the third swing arm in the world coordinate system, respectively. 4 and 4 They respectively represent the X-axis coordinate and the Y-axis coordinate of the end of the fourth swing arm in the world coordinate system. The conversion of the coordinate system is a prior art and will not be described in detail here.

[0133] The above steps calculate a reference support force, i.e., the theoretical support force in this application, through a virtual model controller. The theoretical support force is only the optimal support force for achieving the target posture, but it is not the optimal support force that the robot can output. On the premise of ensuring that the center of mass of the robot is relatively stationary, the 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. The above method can avoid the problem of solving the Jacobian inverse matrix, and can also ensure the stability of the fuselage posture as much as possible.

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

[0135] Determine the target output torque of the swing arm motor of the eight-degree-of-freedom wheel-legged robot 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] Among them, τ ω represents the target output torque of the hub motor, r represents the wheel radius of the 8-DOF 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] Among them, 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 transposed matrix;

[0142] The calculation process of the Jacobian matrix is ​​a prior art and will not be described in detail here;

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

[0144] In this embodiment, in step S4, the controller in the eight-degree-of-freedom wheel-legged robot controls the wheel hub motor and the swing arm motor to output the corresponding target output torque; the above method can achieve the target moving speed, target rotation angle, target height and 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, simulation experiments of various working conditions were carried out on the eight-degree-of-freedom wheel-legged robot in the Webots simulation environment, and joint virtual model control was used as the control group. Joint virtual model control refers to the use of virtual model control (Virtual model control, VMC) to control the robot's wheels and legs. Virtual model control is an existing technology for controlling robots and is not described here. Various working conditions include slope conditions, unstructured terrain conditions, and posture tracking conditions. 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 comparability with actual applications. Table 1 is as follows:

[0146]

[0147] Table 1 Parameters of the eight-degree-of-freedom wheel-legged robot model

[0148] In the experiment, the control frequency was set to 0.5kHz to ensure the response speed of real-time control. The sensor's range, resolution, and noise characteristics were all set within a reasonable range to be close to the actual application environment. At the same time, key parameters such as the motor's torque and speed were consistent with the actual motor, ensuring that the simulation data had 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 structural design.

[0149] Slope working condition experiment: In the simulation environment, a 14° slope and a 80mm high single-side bridge slope working condition experimental scene were built respectively, and a comparative simulation experiment of the joint virtual model control of the eight-degree-of-freedom wheel-legged robot under the working condition and the control method of the present application was carried out. The k of the joint virtual model was set to p =3.5, k d = 0.5; Based on the height of the single-sided 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-sided bridge, it will have a roll angle of about 11.4°. Figure 4 As shown in (a), in the 14° slope condition, the control method of the present application is more effective in maintaining the horizontal stability of the vehicle body posture than the joint virtual model control, and quickly adjusts its pitch angle from -14° to -0.25°; Figure 4 As shown in (b), in the single-sided bridge working condition, the control method of the present application can quickly adjust its roll angle from -11.8° to -0.43° and maintain horizontal stability compared with the joint virtual model control; the experiment proves that the use of the wheel-leg structure and the control method of the present application can effectively avoid tipping over or loss of balance caused by excessive posture tilt, and significantly improve the environmental adaptability and posture stability of the robot.

[0150] Unstructured terrain working condition experiment: An unstructured terrain working condition experimental scene was built in the simulation environment, and single-sided obstacle working condition, double-sided obstacle working condition, impact disturbance working condition and random road working condition simulation experiments were carried out. The experimental group adopted the control method of this application, and the control group adopted the joint virtual model control method. The control parameter of the joint virtual model was set to k. p =3.5, k d =0.5; the obstacle height of the single-side obstacle condition and the double-side obstacle condition in the simulation is 50 mm; the vertical impact force applied in the impact disturbance condition is 5.79 kg.m / s, the lateral and longitudinal impact forces are 3.43 kg·m / s, and the undulation amplitude of the terrain constructed by the random road condition is 0-0.13 m.

[0151] Figure 5 (a) and (b) show the relevant data of the eight-degree-of-freedom wheel-legged robot in the single-sided obstacle working condition. It can be seen from the change of posture angle that the control method of the present application can effectively suppress the disturbance response of the robot's roll angle and pitch angle when passing through a single-sided obstacle compared with the joint virtual model control method. Among them, 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°. The body posture quickly returns to a balanced state. In comparison, the wheel-legged mobile robot controlled by the joint virtual model has obvious roll and pitch angle fluctuations and poor stability.

[0152] Figure 6 (a) and (b) show the relevant data of the eight-degree-of-freedom wheeled-legged robot in the bilateral obstacle working condition. It can be seen from the change of posture angle that the control method of the present application can more effectively suppress the disturbance response of the pitch angle of the mobile robot when passing through bilateral obstacles, among which the pitch angle fluctuation is reduced from a maximum of 8.1° to -0.65°, ensuring that the body posture quickly returns to a balanced state. The robot controlled by the joint virtual model has obvious pitch angle fluctuations and poor stability.

[0153] Figure 7 (a), (b) and (c) show the relevant data of a series of experimental scenarios of impact and recovery of stability on the vertical, lateral and longitudinal surfaces of the 8-DOF wheeled-legged robot. The impact force on the vertical surface is 5.79kg·m / s, and the impact force on the lateral and longitudinal surfaces is 3.43kg·m / s. It can be seen from the change of posture angle that when subjected to external impact, the control method of the present application is compared with the joint virtual model control, and the robot can quickly adjust its posture and restore balance, and has better dynamic stability against impact.

[0154] Figure 8(a) and (b) show the relevant data of the eight-degree-of-freedom wheel-legged robot under random road conditions. It can be seen from the changes in posture angles that the control method of the present application can effectively suppress the disturbance response of the robot's pitch angle and roll angle under random road conditions compared with the joint virtual model control. Among them, 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 body posture quickly returns to a balanced state.

[0155] Attitude tracking experiment: Under the control method of this application, the following experiments were carried out: the roll angle sinusoidal signal tracking, the pitch angle sinusoidal signal tracking, and the attitude angle tracking experiment combining the roll angle and the pitch angle, with the sinusoidal amplitude of 5.73°; ​​during the simulation experiment, the actual body attitude angle was measured by the IMU added to the simulation environment. Fig. 9 As shown in the figure, under the roll angle tracking condition, the average errors at the peak and trough of the sine wave are both 0.03°; under the pitch angle tracking condition, the average errors at the peak and trough of the sine wave are both about 0.01°; the comprehensive average error of the pitch angle tracking while tracking the roll angle is 0.02°, which proves that the control strategy has good dynamic response performance and can effectively follow the expected trajectory.

[0156] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A control method for an eight-degree-of-freedom wheel-legged robot, characterized in that: The following steps are involved: S1. Obtaining target control information of the eight-degree-of-freedom wheel-legged robot; The target control information includes target moving speed, target rotation angle, target height and target rotation angular speed; S2. Determine the target forward force according to the target moving speed and the target rotation angle; determining a target support force according to a target height, a target rotation angular velocity, and a target rotation angle; S3. Determine the target output torque of the wheel hub motor of the eight-degree-of-freedom wheel-legged robot according to the target forward force; Determine the target output torque of the swing arm motor of the eight-degree-of-freedom wheel-legged robot according to the target support force; S4. The controller in the eight-degree-of-freedom wheel-legged robot controls the wheel hub motor and the swing arm motor to output the corresponding target output torque.

2. The control method of the eight-degree-of-freedom wheel-legged robot according to claim 1, characterized in that: The eight-degree-of-freedom wheel-leg robot comprises four wheel-leg structures, four swing arm motors, four wheel hub motors, a body and a controller; The wheel-leg structure includes a swing arm connecting rod and a wheel; One end of the swing arm connecting rod is fixedly connected to the center of the wheel, and the other end of the swing arm connecting rod is connected to the power output end of the swing arm motor, so as to change the posture of the eight-degree-of-freedom wheel-legged robot; The wheel is connected to the power output end of the wheel hub motor and is used to change the travel direction and travel speed of the eight-degree-of-freedom wheel-legged robot; 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 control-connected to the controller; A wheel-leg structure is correspondingly arranged on each of the four sides of the fuselage.

3. The control method of the eight-degree-of-freedom wheel-legged robot according to claim 2, characterized in that: Before obtaining the target control information of the eight-degree-of-freedom wheel-legged robot, it is also necessary to establish a center of mass coordinate system. 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. The Y axis of the center of mass coordinate system is determined by the right-hand rule.

4. The control method of the eight-degree-of-freedom wheel-legged robot according to claim 3, characterized in that: 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. The target rotation angle includes the target rotation angle of the center of mass of the eight-degree-of-freedom wheel-legged robot rotating around the X-axis The target rotation angle around the Y axis and the target rotation angle around the 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 rotational angular velocity includes the target rotational angular velocity of the center of mass of the eight-degree-of-freedom wheel-legged robot rotating around the X-axis and the target rotation angular velocity around the Y axis 5. The control method of the eight-degree-of-freedom wheel-legged robot according to claim 4, characterized in that: The target forward force is obtained by the following steps: 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 ; Among them, k pv Represents the parameters of the PD controller, V x Indicates the actual velocity of the center of mass in the X-axis direction; S212. Based on the PD controller, according to the target rotation angle of rotation around the Z axis Calculate the target torque T of the center of mass around the Z axis z ; Among them, k pw and k dw Both represent the parameters of the PD controller, φ z Indicates the actual angle of rotation of the center of mass around the Z axis, Indicates the actual angular velocity of the center of mass rotating around the Z axis; S213. According to the target traction force F x and the target torque T of the center of mass around the Z axis z Calculate the target forward force using the following formula: Among them, F ω Indicates the target forward force, F ω1 、F ω2 、F ω3 and F ω4 Corresponding to the target forward force output by the first to fourth wheel hub motors, W 2,1 , W 2,2 , W 2,3 and W 2,4 They correspond to the Y-direction distances from the rotation centers of the first to fourth swing arm links to the center of mass; The first hub motor refers to the hub motor on the left front of the eight-degree-of-freedom wheel-legged robot. In counterclockwise order, they are the second hub motor, the third hub motor and the fourth hub motor. The setting order of the swing arm connecting rod is consistent with the setting order of the hub motor.

6. The control method of the eight-degree-of-freedom wheel-legged robot according to claim 4, characterized in that: The target support force is determined by the following method: S221. Determine the target acceleration of the center of mass on the Z axis according to the target height Determine the target rotation angular acceleration of the center of mass around the X-axis based on the target rotation angular velocity and the target rotation angle and the target rotation angular acceleration on the Y axis S222. According to the target acceleration Target rotation angular acceleration and Determine the theoretical attitude control matrix F d , the theoretical attitude control matrix is ​​as follows: Among them, F z Indicates the theoretical support force, F z1 、F z2 、F z3 and F z4 Respectively represent the theoretical support force output by the motors of the first to fourth swing arms, 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 body mass of the eight-degree-of-freedom wheel-legged robot, and I G represents the equivalent moment of inertia of the center of mass, and g represents the acceleration due to gravity; The first swing arm motor refers to the swing arm motor on the left front of the 8-DOF wheel-legged robot. In counterclockwise order, the motors are the second swing arm motor, the third swing arm motor, and the fourth swing arm motor. S223. Construct the objective function and transform the theoretical attitude control matrix F d Substitute into the objective function, and when the objective function reaches the minimum value, output the target support force F z ', the formula is 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 ′≤F z,max Among them, W represents the objective function, T represents the transposed matrix, Q and R both represent the weight matrix, and T min Indicates the lower limit of the swing arm motor output, T max Indicates the output upper limit of the swing arm motor, F z,max Indicates the upper limit of the support force, x1 and y1 represent the X-axis coordinate and Y-axis coordinate of the end of the first swing arm in the world coordinate system, respectively; x2 and y2 represent the X-axis coordinate and Y-axis coordinate of the end of the second swing arm in the world coordinate system, respectively; x3 and y3 represent the X-axis coordinate and Y-axis coordinate of the end of the third swing arm in the world coordinate system, respectively; x4 and y4 represent the X-axis coordinate and Y-axis coordinate of the end of the fourth swing arm in the world coordinate system, respectively.

7. The control method of the eight-degree-of-freedom wheel-legged robot according to claim 6, characterized in that: The target acceleration of the center of mass on the Z axis and the target rotational angular acceleration of the center of mass around the X axis and the Y axis are determined by the following method: The actual moving speed V of the center of mass on the Z axis z , Target height and the actual height H z , the target rotation angle of the center of mass around the X axis Actual angle φ x , target rotation angular velocity and the actual angular velocity And the target rotation angle of the center of mass around the Y axis Actual angle φ y , target rotation angular velocity and the actual angular velocity After conversion to 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 the data converted to the world coordinate system. The calculation formula is as follows: in, represents the target acceleration of the center of mass on the Z axis, Indicates the target rotation angular acceleration of the center of mass around the X axis, Indicates the target rotation 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 actual height in the world coordinate system, Indicates the actual moving speed in the world coordinate system. and They represent the target rotation angle, actual angle, and 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 They 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 in the world coordinate system.

8. The control method of the eight-degree-of-freedom wheel-legged robot according to claim 5, characterized in that: The target output torque of the hub motor is determined by the following formula: t ω =F ω r Among them, 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.

9. The control method of the eight-degree-of-freedom wheel-legged robot according to claim 7, characterized in that: The target output torque of the swing arm motor is calculated by the following formula: t s =J T F z ' Among them, τ s It 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 transposed matrix.

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