Single-leg sliding mode control method for quadruped robot based on disturbance observer

Abstract

The invention relates to a quadruped robot single-leg sliding mode control method based on a disturbance observer, and belongs to the technical field of robot control. Firstly, a foot end track of a single leg of the quadruped robot in a swinging stage is established; then, establishing a kinematics model of a single leg of the quadruped robot to realize conversion between a foot end target position and a corresponding joint angle; on the basis, a nonsingular terminal sliding mode controller is designed to cope with dynamic control under the non-interference condition; finally, a final composite control strategy is designed in combination with a sliding mode controller and interference estimation, stable tracking of the joint angle of the robot is achieved, and therefore the anti-interference performance of the single-leg system is improved. According to the method, a composite controller is designed by combining a finite time disturbance observer and a nonsingular terminal sliding mode controller, so that the foot end trajectory tracking precision and the system robustness of the quadruped robot are improved, and the uncertainty caused by external disturbance and modeling errors of the robot is eliminated.

Description

Technical Field

[0001] The invention belongs to the technical field of robot control and relates to a single-leg sliding mode control method of a quadruped robot based on an interference observer. Background Art

[0002] Quadruped robots have advantages such as good stability and strong adaptability, and their performance in complex terrain is better than that of traditional wheeled or tracked robots. With the development of robotics technology, how to achieve stable control of quadruped robots has become a research focus. Among them, accurate tracking of the foot trajectory is also crucial. Traditional foot trajectory tracking control methods, such as the proportional-derivative controller (PD) controller based on virtual models, often find it difficult to simultaneously take into account tracking accuracy and robustness of the control system when facing complex external disturbances and uncertainties. Sliding mode control, as a nonlinear control method, is widely used in the field of robot control due to its strong robustness to system parameter uncertainty and external disturbances. However, the traditional sliding mode control method has limited convergence and anti-interference, and the terminal sliding mode has a singularity problem. For this reason, the non-singular terminal sliding mode controller (NTSMC) was proposed. By designing a special sliding mode surface, the system state converges within a finite time, thereby improving the response speed and accuracy of the control system. However, when NTSMC is used alone, it still cannot completely eliminate the impact of external disturbances on the system. In order to further enhance the robustness of single-leg trajectory tracking of quadruped robots, the finite time disturbance observer (FTDO) is used as an effective compensation strategy to estimate and compensate external disturbances in real time. Combining the finite time disturbance observer with a non-singular terminal sliding mode controller can better cope with foot-end trajectory tracking tasks in complex environments and improve the stability and control accuracy of the system. Therefore, in response to the needs of single-leg trajectory tracking of quadruped robots, a control method combining the finite time disturbance observer and the non-singular terminal sliding mode is required to achieve higher accuracy and robustness of foot-end trajectory tracking control. Summary of the invention

[0003] In view of this, the purpose of the present invention is to provide a single-leg sliding mode control method for a quadruped robot based on a disturbance observer, and to design a composite controller by combining a finite-time disturbance observer with a non-singular terminal sliding mode controller to improve the foot-end trajectory tracking accuracy and system robustness of the quadruped robot, and eliminate the uncertainty caused by external disturbances and modeling errors to the robot.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] A single-leg sliding mode control method for a quadruped robot based on a disturbance observer comprises the following steps:

[0006] Establish the foot trajectory of a single leg of a quadruped robot during the swing phase;

[0007] Establish a kinematic model of a single leg of a quadruped robot to achieve the conversion between the target position of the foot end and the corresponding joint angle;

[0008] Establish the dynamic model of a single leg of a quadruped robot;

[0009] Establish a non-singular sliding mode controller for a single-leg quadruped robot without interference;

[0010] Estimate the unknown disturbance of the system through the finite-time disturbance observer;

[0011] A single-leg composite controller for a quadruped robot is designed to achieve stable tracking of the robot's preset joint angles in the presence of interference.

[0012] The single leg of the quadruped robot is composed of three connecting rods, namely the hip, thigh and calf, which are connected to the body joints, and these three connecting rods constitute corresponding joints respectively; the hip joint is responsible for the movement of the single leg of the quadruped robot in the left and right directions, and the thigh and calf joints are responsible for the movement of the single leg of the quadruped robot in the front and back directions.

[0013] The steps of establishing the foot end trajectory of a single leg of the quadruped robot in the swinging phase are specifically as follows:

[0014] The foot end trajectory of the single leg of the quadruped robot in the swing phase is established and expressed as the following formula:

[0015]

[0016]

[0017] Among them, x t (t) is the x-direction trajectory of the foot end, z f (t) is the z-direction trajectory of the foot end; x0 is the initial position of the foot end in the x direction, x T is the end position of the foot in the x direction; z0 is the initial position of the foot in the z direction, h is the height of the middle control point of the foot in the z direction; T f is the duration of the foot trajectory.

[0018] The steps of establishing the kinematic model of a single leg of a quadruped robot to realize the conversion between the target position of the foot end and the corresponding joint angle are specifically as follows:

[0019] Assume that the hip joint coordinate system is {1}, the thigh joint coordinate system is {2}, the calf joint coordinate system is {3}, the foot end coordinate system is {4}, and the base coordinate system is {0}; the origins of the coordinate systems {0}, {1}, and {2} are set on the axis of the body joint and the thigh joint; the relationship between the foot end with the foot end coordinate system {4} as the origin and the angles of each joint is expressed as the following formula:

[0020]

[0021]

[0022] Among them, x p ,y p , z p are the degrees of freedom of the foot end in the x, y, and z directions respectively; L1, L2, and L3 are the lengths of the hip, thigh, and calf joints respectively; θ1, θ2, and θ3 are the rotation angles of the hip, thigh, and calf joints respectively;

[0023] The inverse kinematics equation of a single leg of a quadruped robot is established and expressed as the following formula:

[0024]

[0025] Wherein, x, y, z are the preset trajectories of the foot end on each coordinate axis, and the calculation process is as follows:

[0026]

[0027]

[0028] n=(lxz' 2 -L3 2 -L2 2 ) / 2*L2

[0029]

[0030] The steps of establishing the dynamic model of a single leg of a quadruped robot are specifically as follows:

[0031] The dynamic equation model of a single leg of a quadruped robot is established and expressed as the following formula:

[0032]

[0033] Among them, M ij is the mass matrix parameter, C ij is the Coriolis force and centripetal force matrix parameter, G i is the gravity matrix parameter, τ i is the moment of each joint; are the joint angular accelerations of the hip, thigh and calf respectively; are the joint angular velocities of the hip, thigh and calf respectively; the calculation process is as follows:

[0034]

[0035]

[0036] M 12 =-L1L2m3sin(θ2)-L1L3a3m3sin(θ2+θ3)-L1L2a2b1m2sin(θ2)

[0037] M 13 =-L1L3a3m3sin(θ2+θ3)

[0038] M 21 =M 12

[0039]

[0040]

[0041] M 31 =M 13

[0042] M 32 =M 23

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052] C 33 =0

[0053] G(0)=-gm2(L1b1cosθ1-L2a2cosθ2sinθ1)

[0054] -gm3(L1cosθ1-L2cosθ2sinθ1+L3a3(sinθ1sinθ2sinθ3-cosθ2cosθ3sinθ1))-L1a1gm1cosθ1

[0055] G(1)=gcosθ1(L2m3sinθ2+L3a3m3sin(θ2+θ3)+L2a2m2sinθ2)

[0056] G(2)=L3a3gm3sin(θ2+θ3)cosθ1

[0057] Among them, I xxi , I yyi , I zzi are the moments of inertia of the hip, thigh and shank links, m i is the mass of each connecting rod, a i is the distance from the center of mass of each connecting rod to the coordinate system where the connecting rod is located, b i is the distance from the center of mass of each link to the coordinate system of the previous link.

[0058] The steps of establishing a non-singular sliding mode controller for a single leg of a quadruped robot without interference are specifically as follows:

[0059] The single-leg composite controller of the quadruped robot is expressed as a dynamic model based on joint angles, as follows:

[0060]

[0061] Where, τ is the joint torque; is the expected joint acceleration; e is the angle tracking error, e = q d -q; c, k, η are positive constants, β>1; s is the sliding surface, which is expressed as the following formula:

[0062]

[0063] is the estimated value of system interference, expressed as the following formula:

[0064]

[0065] Among them, α1, α2, α3>0 are gain coefficients, 0<h<1;

[0066] In the absence of interference, the single-leg controller of the quadruped robot is a non-singular terminal sliding mode controller, which is expressed as a dynamic model based on the joint angle, expressed as the following formula:

[0067]

[0068] The step of estimating the unknown disturbance of the system by using the finite time disturbance observer is specifically as follows:

[0069] Define vector z, expressed as the following formula:

[0070]

[0071] in, is the joint angular velocity, and the derivative value of p is expressed as follows:

[0072]

[0073] in, is the perturbed observation value, expressed as the following formula:

[0074]

[0075] Among them, α1, α2, α3>0 are gain coefficients, and 0<h<1.

[0076] The steps of designing a single-leg composite controller of a quadruped robot in a disturbed state to achieve stable tracking of a preset joint angle of the robot are specifically as follows:

[0077] In the presence of interference, the single-leg dynamics equation of the quadruped robot is expressed as follows:

[0078]

[0079] Among them, ΔM, ΔC, and ΔG represent the uncertainty of system model parameters;

[0080] The concentrated disturbance d composed of model uncertainty, joint friction and load change is expressed as follows:

[0081]

[0082] Combining the observer with the non-singular terminal sliding mode controller, the single-leg composite controller of the quadruped robot is expressed as a dynamic model based on the joint angle, which is expressed as the following formula:

[0083]

[0084] The following formula is further obtained:

[0085]

[0086] The beneficial effects of the present invention are:

[0087] The combination of a finite-time disturbance observer and a non-singular terminal sliding mode controller effectively improves the accuracy of the foot-end trajectory tracking and the system robustness of the quadruped robot in complex environments. This composite control strategy can eliminate the uncertainty caused by external disturbances and modeling errors, and achieve stable tracking of the robot's joint angles. By establishing a detailed kinematic and dynamic model of a single leg of a quadruped robot, the conversion between the foot-end target position and the corresponding joint angle can be accurately achieved, providing a solid foundation for subsequent control strategies.

[0088] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0090] Figure 1 A three-dimensional spatial diagram of the trajectory of the right front leg foot end of a quadruped robot preset in a specific embodiment of the present invention;

[0091] Figure 2 A schematic diagram of a single leg of a quadruped robot according to a specific embodiment of the present invention;

[0092] Figure 3 This is a control flow chart of a single-leg composite controller of a quadruped robot according to a specific embodiment of the present invention;

[0093] Figure 4 A three-dimensional spatial comparison diagram of the foot end trajectory during the control process based on the virtual model controller and the composite controller according to a specific embodiment of the present invention;

[0094] Figure 5 A comparison diagram of the foot end trajectory in the x direction during the control process based on the virtual model controller and the composite controller according to a specific embodiment of the present invention;

[0095] Figure 6 A comparison diagram of the y direction of the foot end trajectory during the control process based on the virtual model controller and the composite controller according to a specific embodiment of the present invention;

[0096] Figure 7 A comparison diagram of the foot end trajectory in the z direction during the control process based on the virtual model controller and the composite controller according to a specific embodiment of the present invention;

[0097] Figure 8 FIG. 1 is a diagram of an interference estimation curve of a finite-time interference observer according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0098] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and the features in the embodiments can be combined with each other without conflict.

[0099] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0100] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0101] The present invention proposes a single-leg sliding mode control method for a quadruped robot based on a disturbance observer. A composite controller is designed by combining a finite-time disturbance observer with a non-singular terminal sliding mode controller to improve the foot-end trajectory tracking accuracy and system robustness of the quadruped robot and eliminate the uncertainty caused by external disturbances and modeling errors on the robot.

[0102] First, the foot-end trajectory of a single leg of a quadruped robot in the swinging phase is established; then, a kinematic model of a single leg of a quadruped robot is established to realize the conversion between the foot-end target position and the corresponding joint angle; then, a dynamic model of the single leg is established; on this basis, a non-singular terminal sliding mode controller is designed to cope with dynamic control in the absence of interference; finally, the sliding mode controller is combined with interference estimation to design the final composite control strategy to achieve stable tracking of the robot's joint angle, thereby improving the anti-disturbance performance of the single-leg system. The specific embodiment includes the following steps:

[0103] Step 1: Establish the foot trajectory of a single leg of the quadruped robot in the swing phase:

[0104] Gait refers to the sequence of movement of the legs of a quadruped robot in time and space, and a periodic gait is usually used on flat ground. The gait cycle refers to the process from the heel of one side touching the ground to the heel of the same side touching the ground again during walking, and is usually divided into two phases: the support phase and the swing phase. The support phase is the phase when the end of the foot touches the ground and bears the weight of the body, and the swing phase is the phase when the end of the foot moves in the air and does not touch the ground.

[0105] The present invention mainly relates to a control method for the swing phase, please refer to Figure 1 , is a three-dimensional spatial diagram of the preset foot end trajectory of the right front leg of a quadruped robot in a specific embodiment of the present invention, where the x-axis represents the forward direction, the y-axis represents the lateral direction, and the z-axis represents the height direction. The preset foot end trajectory of this embodiment is the trajectory of the swinging stage, which is expressed as the following formula:

[0106]

[0107]

[0108] Among them, x t (t) is the x-direction trajectory of the foot end, z f (t) is the z-direction trajectory of the foot end; x0 is the initial position of the foot end in the x direction, x T is the end position of the foot in the x direction; z0 is the initial position of the foot in the z direction, h is the height of the middle control point of the foot in the z direction; T f is the duration of the foot trajectory.

[0109] Step 2: Establish a single-leg kinematic model of a quadruped robot:

[0110] See also Figure 2 , is a schematic diagram of a quadruped robot leg according to a specific embodiment of the present invention. The quadruped robot leg is mainly composed of three connecting rods, hip, thigh and calf, connected to the body joint. These three connecting rods constitute corresponding joints. Among them, the hip joint is mainly responsible for the movement of the quadruped robot leg in the left and right directions, and the thigh and calf joints are responsible for the movement of the quadruped robot leg in the front and back directions. Figure 2 As shown, the hip joint coordinate system is {1}, the thigh joint coordinate system is {2}, the calf joint coordinate system is {3}, and the foot end coordinate system is {4}. In addition, the {0} coordinate system is defined as the base coordinate system. In order to simplify the homogeneous transformation matrix between the coordinate systems, the origins of the coordinate systems {0}, {1}, and {2} are all placed on the axis between the body joint and the thigh joint. Then the relationship between the foot end of the quadruped robot with the coordinate system {4} as the origin and the angles of each joint is expressed as the following formula:

[0111]

[0112]

[0113] Among them, x p is the degree of freedom of the foot end in the x direction, y p is the degree of freedom of the foot end in the y direction, z p is the degree of freedom of the foot in the z direction; L1 is the length of the hip joint of the quadruped robot leg, L2 is the length of the thigh joint of the quadruped robot leg, and L3 is the length of the calf joint of the quadruped robot leg; θ1 is the rotation angle of the hip joint of the quadruped robot leg, θ2 is the rotation angle of the thigh joint of the quadruped robot leg, and θ3 is the rotation angle of the calf joint of the quadruped robot leg.

[0114] In order to convert the preset foot end trajectory into joint angle for control, the inverse kinematics equation of a single leg of a quadruped robot is expressed as follows:

[0115]

[0116] Among them, x, y, z are the preset trajectories of the foot end on each coordinate axis; the calculation process of other parameters is as follows:

[0117]

[0118]

[0119] n=(lxz' 2 -L3 2 -L2 2 ) / 2*L2

[0120]

[0121] Step 3: Establish the dynamic equation model of the single leg of the quadruped robot according to the joint parameters, which can be expressed as the following formula:

[0122]

[0123] Among them, M ij is the mass matrix parameter, C ij is the Coriolis force and centripetal force matrix parameter, G i is the gravity matrix parameter, τ i is the moment of each joint; are the joint angular accelerations of the hip, thigh and shank of the quadruped robot’s legs, respectively; are the joint angular velocities of the hip, thigh and calf of the quadruped robot. The calculation process of each parameter is as follows:

[0124]

[0125] M 12 =-L1L2m3sin(θ2)-L1L3a3m3sin(θ2+θ3)-L1L2a2b1m2sin(θ2)

[0126] M 13 =-L1L3a3m3sin(θ2+θ3)

[0127] M 21 =M 12

[0128]

[0129]

[0130] M 31 =M 13

[0131] M 32 =M 23

[0132]

[0133]

[0134]

[0135]

[0136]

[0137]

[0138]

[0139]

[0140]

[0141] C 33 =0

[0142] G(0)=-gm2(L1b1cosθ1-L2a2cosθ2sinθ1)

[0143] -gm3(L1cosθ1-L2cosθ2sinθ1+L3a3(sinθ1sinθ2sinθ3-cosθ2cosθ3sinθ1))-L1a1gm1cosθ1

[0144] G(1)=gcosθ1(L2m3sinθ2+L3a3m3sin(θ2+θ3)+L2a2m2sinθ2)

[0145] G(2)=L3a3gm3sin(θ2+θ3)cosθ1

[0146] Among them, I xxi , I yyi , I zzi are the moments of inertia of the hip, thigh and shank links of the quadruped robot, respectively, m i represents the mass of each connecting rod, a i represents the distance from the center of mass of each connecting rod to the coordinate system where the connecting rod is located, b i is the distance from the center of mass of each link to the coordinate system of the previous link.

[0147] Step 4: Design a single-leg composite controller for a quadruped robot:

[0148] Since the output of the quadruped robot single-leg composite controller is the joint torque of the hip, thigh and calf of the quadruped robot leg, the quadruped robot single-leg composite controller can be expressed as a dynamic model based on the joint angle, which is expressed as the following formula:

[0149]

[0150] Where, τ is the joint torque; is the expected joint acceleration; e is the angle tracking error, e = q d -q; c, k, η are positive constants, β>1; s is the sliding surface, which is expressed as the following formula:

[0151]

[0152] is the estimated value of system interference, expressed as the following formula:

[0153]

[0154] Among them, α1, α2, α3>0 are gain coefficients, and 0<h<1.

[0155] Design a single-leg composite controller for a quadruped robot, which includes the following steps:

[0156] 1) Design a non-singular sliding mode controller for a single-leg quadruped robot without interference:

[0157] In the case of no interference, according to the single-leg dynamics model of the quadruped robot, the single-leg composite controller of the quadruped robot is a non-singular terminal sliding mode controller, which is expressed as a dynamic model based on the joint angle, expressed as the following formula:

[0158]

[0159] 2) Design a finite-time disturbance observer:

[0160] The finite-time disturbance observer is used to estimate the unknown disturbance of the system, thereby improving the robustness of the control system. First, in order to facilitate the design of the observer, the vector z is defined and expressed as the following formula:

[0161]

[0162] in, is the joint angular velocity, and the derivative value of p is expressed as follows:

[0163]

[0164] in, is the perturbed observation value, expressed as the following formula:

[0165]

[0166] Among them, α1, α2, α3>0 are gain coefficients, and 0<h<1.

[0167] 3) Design a single-leg composite controller for a quadruped robot under interference conditions:

[0168] Considering the interference, the single-leg dynamic equation of the quadruped robot is expressed as follows:

[0169]

[0170] Among them, ΔM, ΔC, and ΔG represent the uncertainty of system model parameters;

[0171] The concentrated disturbance d composed of model uncertainty, joint friction and load change is expressed as follows:

[0172]

[0173] Combining the observer with the non-singular terminal sliding mode controller, the single-leg composite controller of the quadruped robot is expressed as a dynamic model based on the joint angle, which is expressed as the following formula:

[0174]

[0175] The following formula is further obtained:

[0176]

[0177] See also Figure 3, which is a control flow chart of a single-leg composite controller of a quadruped robot according to a specific embodiment of the present invention, shows the working principle of trajectory tracking of the single-leg end of the quadruped robot: first, the expected trajectory of the foot end is calculated using a trajectory generator; then, the expected trajectory is converted into the angular rotation of each joint using the single-leg inverse kinematics equation; then, the expected angle is subtracted from the actual angle to obtain the angle error, and a non-singular terminal sliding mode controller is built by combining four sets of robot single-leg dynamics equations; on this basis, a finite-time disturbance observer is established to estimate the unmodeled dynamics and disturbances of the system, and the final composite control strategy is designed.

[0178] See also Figure 4 , which is a three-dimensional spatial comparison diagram of the foot end trajectory during the control process based on the virtual model controller and the composite controller according to a specific embodiment of the present invention; please refer to Figures 5 to 7 , which is a comparison diagram of the x, y, and z directions of the foot end trajectory during the control process based on the virtual model controller and the composite controller according to a specific embodiment of the present invention.

[0179] 0.1s after starting the system, interference is applied to both the virtual model-based controller and the composite controller. Figures 4 to 7 From the tracking performance of each controller in the example, it can be seen that the trajectory tracking error of the controller based on the virtual model is large, and it is difficult to meet the effect of accurately tracking the desired curve; while the composite controller can accurately track the desired curve after being disturbed, and its trajectory tracking effect is still good. Therefore, the composite controller of this embodiment can effectively suppress interference and improve the robustness of the system.

[0180] See also Figure 8 , which is a disturbance estimation curve diagram of a finite time disturbance observer according to a specific embodiment of the present invention. It can be seen from the external disturbance curve and the estimated disturbance curves of each joint that the joint torque estimated by the finite time disturbance observer is substantially coincident with the given joint torque curve. Therefore, the estimation effect of the unknown disturbance of the estimation system of the finite time disturbance observer proposed by the present invention is good.

[0181] The present invention combines a finite-time disturbance observer with a non-singular terminal sliding mode controller, effectively improving the accuracy of foot-end trajectory tracking and system robustness of a quadruped robot in complex environments. This composite control strategy can eliminate the uncertainty caused by external disturbances and modeling errors, and achieve stable tracking of the robot's joint angles. By establishing a detailed kinematic and dynamic model of a single leg of a quadruped robot, the conversion between the foot-end target position and the corresponding joint angle can be accurately achieved, providing a solid foundation for subsequent control strategies. Experimental results show that the composite controller can still maintain a good trajectory tracking effect under interference, which is significantly better than the traditional control method based on a virtual model. The interference estimation curve of the finite-time disturbance observer is highly consistent with the actual interference, which further verifies the effectiveness and accuracy of this method.

[0182] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A single-leg sliding mode control method for a quadruped robot based on a disturbance observer, characterized in that: The following steps are involved: Establish the foot trajectory of a single leg of a quadruped robot during the swing phase; Establish a kinematic model of a single leg of a quadruped robot to achieve the conversion between the target position of the foot end and the corresponding joint angle; Establish the dynamic model of a single leg of a quadruped robot; Establish a non-singular sliding mode controller for a single-leg quadruped robot without interference; Estimate the unknown disturbance of the system through the finite-time disturbance observer; A single-leg composite controller for a quadruped robot is designed to achieve stable tracking of the robot's preset joint angles in the presence of interference.

2. The single-leg sliding mode control method of a quadruped robot based on a disturbance observer according to claim 1, characterized in that: The single leg of the quadruped robot is composed of three connecting rods, namely the hip, thigh and calf, which are connected to the body joints, and these three connecting rods constitute corresponding joints respectively; the hip joint is responsible for the movement of the single leg of the quadruped robot in the left and right directions, and the thigh and calf joints are responsible for the movement of the single leg of the quadruped robot in the front and back directions.

3. The single-leg sliding mode control method of a quadruped robot based on a disturbance observer according to claim 2 is characterized in that: The steps of establishing the foot end trajectory of a single leg of the quadruped robot in the swinging phase are specifically as follows: The foot end trajectory of the single leg of the quadruped robot in the swing phase is established and expressed as the following formula: Among them, x t (t) is the x-direction trajectory of the foot end, z f (t) is the z-direction trajectory of the foot end; x0 is the initial position of the foot end in the x direction, x T is the end position of the foot in the x direction; z0 is the initial position of the foot in the z direction, h is the height of the middle control point of the foot in the z direction; T f is the duration of the foot trajectory.

4. The single-leg sliding mode control method of a quadruped robot based on a disturbance observer according to claim 3 is characterized in that: The steps of establishing the kinematic model of a single leg of a quadruped robot to realize the conversion between the target position of the foot end and the corresponding joint angle are specifically as follows: Assume that the hip joint coordinate system is {1}, the thigh joint coordinate system is {2}, the calf joint coordinate system is {3}, the foot end coordinate system is {4}, and the base coordinate system is {0}; the origins of the coordinate systems {0}, {1}, and {2} are set on the axis of the body joint and the thigh joint; the relationship between the foot end with the foot end coordinate system {4} as the origin and the angles of each joint is expressed as the following formula: Among them, x p ,y p , z p are the degrees of freedom of the foot end in the x, y, and z directions respectively; L1, L2, and L3 are the lengths of the hip, thigh, and calf joints respectively; θ1, θ2, and θ3 are the rotation angles of the hip, thigh, and calf joints respectively; The inverse kinematics equation of a single leg of a quadruped robot is established and expressed as the following formula: Among them, x, y, z are the preset trajectories of the foot end on each coordinate axis, and the calculation process is as follows:

5. The single-leg sliding mode control method of a quadruped robot based on a disturbance observer according to claim 4 is characterized in that: The steps of establishing the dynamic model of a single leg of a quadruped robot are specifically as follows: The dynamic equation model of a single leg of a quadruped robot is established and expressed as the following formula: Among them, M ij is the mass matrix parameter, C ij is the Coriolis force and centripetal force matrix parameter, G i is the gravity matrix parameter, τ i is the moment of each joint; are the joint angular accelerations of the hip, thigh and calf respectively; are the joint angular velocities of the hip, thigh and calf respectively; the calculation process is as follows: M 12 =-L1L2m3 sin(θ2)-L1L3a3m3 sin(θ2+θ3)-L1L2a2b1m2 sin(θ2) M 13 =-L1L3a3m3 sin(θ2+θ3) M 21 =M 12 M 31 =M 13 M 32 =M 23 C 33 ＝0 G(0)=-gm2(L1b1cosθ1-L2a2cosθ2sinθ1) -gm3(L1cosθ1-L2cosθ2sinθ1+L3a3(sinθ1sinθ2sinθ3-cosθ2cosθ3sinθ1))-L1a1gm1cosθ1G(1)=gcosθ1(L2m3sinθ2+L3a3m3sin(θ2+θ3)+L2a2m2sinθ2) G(2)=L3a3gm3sin(θ2+θ3)cosθ1 Among them, I xxi ,I yyi ,I zzi are the moments of inertia of the hip, thigh and shank links, m i is the mass of each connecting rod, a i is the distance from the center of mass of each connecting rod to the coordinate system where the connecting rod is located, b i is the distance from the center of mass of each link to the coordinate system of the previous link.

6. The single-leg sliding mode control method of a quadruped robot based on a disturbance observer according to claim 5 is characterized in that: The steps of establishing a non-singular sliding mode controller for a single leg of a quadruped robot without interference are specifically as follows: The single-leg composite controller of the quadruped robot is expressed as a dynamic model based on joint angles, as follows: Where, τ is the joint torque; is the expected joint acceleration; e is the angle tracking error, e = q d -q; c, k, η are positive constants, β>1; s is the sliding surface, which is expressed as the following formula: is the estimated value of system interference, expressed as the following formula: Among them, α1, α2, α3>0 are gain coefficients, 0<h<1; In the absence of interference, the single-leg controller of the quadruped robot is a non-singular terminal sliding mode controller, which is expressed as a dynamic model based on the joint angle, expressed as the following formula:

7. The single-leg sliding mode control method of a quadruped robot based on a disturbance observer according to claim 6 is characterized in that: The step of estimating the unknown disturbance of the system by using the finite time disturbance observer is specifically as follows: Define vector z, expressed as the following formula: in, is the joint angular velocity, and the derivative value of p is expressed as follows: in, is the perturbed observation value, expressed as the following formula: Among them, α1, α2, α3>0 are gain coefficients, and 0<h<1.

8. The single-leg sliding mode control method of a quadruped robot based on a disturbance observer according to claim 7 is characterized in that: The steps of designing a single-leg composite controller of a quadruped robot in a disturbed state to achieve stable tracking of a preset joint angle of the robot are specifically as follows: In the presence of interference, the single-leg dynamics equation of the quadruped robot is expressed as follows: Among them, ΔM, ΔC, and ΔG represent the uncertainty of system model parameters; The concentrated disturbance d composed of model uncertainty, joint friction and load change is expressed as follows: Combining the observer with the non-singular terminal sliding mode controller, the single-leg composite controller of the quadruped robot is expressed as a dynamic model based on the joint angle, which is expressed as the following formula: The following formula is further obtained:

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