A variable stiffness control method for hydraulic leg SLIP model that can adapt to different stiffness ground

Abstract

The present invention relates to a variable stiffness control method of a hydraulic leg SLIP model that can adapt to different rigidity grounds, which comprises the following steps: obtaining the leg stiffness in the Cartesian space z direction under different ground stiffnesses based on the series total stiffness; introducing the SLIP model to obtain the variable stiffness parameters of the SLIP model from the foot end to the center of mass; respectively constructing the stiffness relationship between the foot end and the generalized force and generalized position of the joint, deriving the mapping relationship between the foot end of the hydraulic leg and the joint equivalent stiffness, and obtaining the joint variable stiffness parameters; establishing the hydraulic leg SLIP model hydraulic cylinder variable stiffness parameters; finally combining the hydraulic leg SLIP model hydraulic cylinder variable stiffness parameters with the environmental variable stiffness parameters to realize variable stiffness control under different environmental stiffnesses. A set of complete corresponding relationships is obtained to obtain the joint to equivalent SLIP stiffness relationship formula, under which the active compliance parameters of the hydraulically driven joint can be accurately adjusted to realize the active variable stiffness control of the joint to adapt to different environmental stiffnesses.

Description

Technical Field

[0001] The invention belongs to the field of robot control, and in particular relates to a variable stiffness control method of a hydraulic leg SLIP model which can adapt to ground surfaces with different stiffnesses. Background Art

[0002] Quadruped mammals have good ability to adapt to terrain and can move flexibly under high loads. Hydraulic quadruped robots are inspired by mammals and have broad application prospects in many fields such as earthquake relief, operations in hazardous environments, and field exploration. These scenarios require robots to adapt to ground of different stiffness to ensure the robot's flexibility and stability.

[0003] Each leg of the hydraulic quadruped bionic robot uses a hydraulic cylinder as a driving unit to drive the single leg movement. The commonly used control method is a high-precision position control method. However, if the position control method is continued when the foot touches the ground or contacts an obstacle, a large impact will be generated, which will cause the quadruped robot to be unstable and even cause damage to the mechanical structure and its accompanying electronic equipment. In addition, the real environment that the robot foot contacts is complex and changeable, especially different ground surfaces have different stiffness, requiring the foot to present different compliance performance to achieve adaptability to the environment. In this case, it is particularly critical to establish the relationship between different environmental compliance parameters and leg compliance models, and to use a variable stiffness control method that adapts to the environment to replace the traditional single position control to improve the robot's ground adaptability.

[0004] The traditional control method is direct position control. The foot-ground contact impact will produce a hard impact that will cause the robot to become unstable or even damaged. The current compliant control method installs passive elastic elements such as springs on the legs, or uses fixed parameter impedance control to simulate spring damping elements, and controls the contact with the ground in a passive manner. However, this method cannot adapt to the movement requirements of ground with different stiffness changes. Due to the nonlinearity of leg joint coupling and hydraulic system, the control element is a hydraulic cylinder on each joint. At present, there is no mapping relationship that associates the foot-end contact stiffness with the joint hydraulic cylinder stiffness, so the foot-end stiffness cannot be accurately controlled. In order to adapt to different stiffness grounds and control the foot-ground contact stiffness by controlling the hydraulic cylinder, it is very important to study a hydraulic leg variable stiffness control method based on the equivalent SLIP model. Summary of the invention

[0005] In order to solve the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a hydraulic leg SLIP model variable stiffness control method that can adapt to different stiffness grounds, which can obtain the leg stiffness in the Cartesian space z direction under different ground stiffnesses based on the total series stiffness; and introduce the SLIP model, according to the generalized force mapping relationship between the foot end of the SLIP model and the hydraulic leg joint, and the mapping relationship between the foot end of the SLIP model and the minimum change amount of the generalized position of the joint, respectively construct the stiffness relationship between the foot end and the joint generalized force and generalized position, derive the mapping relationship between the foot end of the hydraulic leg and the joint equivalent stiffness, and obtain the joint variable stiffness parameters; and further derive the mapping relationship between each joint of the hydraulic leg and the equivalent stiffness of the hydraulic cylinder, and combine the joint variable stiffness parameters to establish the hydraulic leg SLIP model hydraulic cylinder variable stiffness parameters, which can accurately adjust the active compliance parameters of the hydraulic drive joint through the established mapping relationship, and realize the active variable stiffness control of the joint to adapt to different environmental stiffness.

[0006] Specifically, the present invention provides a variable stiffness control method of a hydraulic leg SLIP model that can adapt to different stiffness grounds, which includes the following steps:

[0007] S1. Calculate the total stiffness of the ground and legs in series in the z direction according to the foot-ground contact force equation. Based on the total stiffness in series, obtain the leg stiffness in the z direction under different ground stiffnesses. The specific calculation formula is as follows:

[0008]

[0009] Among them, K z K is the total stiffness of the ground and legs in series in the z direction, zg is the ground stiffness in the z direction, K zl is the leg stiffness in z direction;

[0010] S2. Introduce the SLIP model, establish the relationship between the leg swing angle and the radial length of the SLIP model, and obtain the variable stiffness parameter of the SLIP model from the foot end to the center of mass according to the leg stiffness in the z direction obtained in step S1. The specific expression is as follows:

[0011]

[0012] Among them, K slip is the variable stiffness parameter of the SLIP model from the foot end to the center of mass; θ is the leg swing angle of the SLIP model;

[0013] S3. According to the generalized force mapping relationship between the foot end and the hydraulic leg joint in the SLIP model and the mapping relationship between the foot end and the minimal change of the generalized position of the joint in the SLIP model, the stiffness relationship between the generalized force of the foot end and the joint and the generalized position of the foot end and the joint are constructed respectively, and the equivalent stiffness mapping relationship between the foot end and the joint is obtained to obtain the joint variable stiffness parameters; the joint variable stiffness parameter matrix K qThe specific calculation formula is:

[0014] K q =J T K slip J+K g

[0015]

[0016] Where J is the Jacobian matrix from the foot end to the joint of the SLIP model; K q is the joint variable stiffness parameter matrix; To find the derivative, (·) T is the transpose of a matrix or vector, is the generalized force at the foot end, the direction is from the foot end to the center of mass, f z is the foot-ground contact force in the z direction, q is the generalized displacement of the joint;

[0017] S4, based on the mapping relationship between the equivalent stiffness of each joint of the hydraulic leg and the hydraulic cylinder, combined with the joint variable stiffness parameter matrix K q , establish the variable stiffness parameters of the hydraulic cylinder of the hydraulic leg SLIP model, and the specific calculation formula is:

[0018] k slip =J -T (Lk hx WK g )J -1 ;

[0019] Among them, k hx is the hydraulic cylinder stiffness matrix, L is the equivalent force arm matrix between the hydraulic cylinder and the joint torque, and W is the length matrix obtained by derivation of the mapping relationship between the joint angle and the hydraulic cylinder elongation;

[0020] S5. Combining the variable stiffness parameters of the hydraulic cylinder of the hydraulic leg SLIP model with the environmental variable stiffness parameters, the actual height is solved to achieve variable stiffness control under different environmental stiffnesses.

[0021] Preferably, the foot-ground contact force equation in step S1 is:

[0022]

[0023] In the formula, f z is the ground contact force in the z direction, Δp z is the total compression of the ground and legs in the z direction, Δp zg is the ground compression in the z direction, Δp zl is the compression of the leg in the z direction.

[0024] Preferably, in step S3, the mapping relationship between the minimum change amount of the generalized force of the foot end of the SLIP model and the hydraulic leg joint is:

[0025] dτ=J T (df)+(dJ T )f

[0026] In the formula, d(·) is the smallest change, (·) T is the transpose of the matrix or vector, τ is the generalized force of the joint;

[0027] Combining stiffness and generalized force, the mapping relationship between the minimum change of the foot end and the generalized force of the joint can be expressed as:

[0028]

[0029] At the same time, eliminate dq to obtain the variable stiffness parameter matrix corresponding to the hydraulic leg joint:

[0030] K q =J T K slip J+K g .

[0031] Preferably, in step S4, the mapping relationship between the equivalent stiffness of each joint of the hydraulic leg and the hydraulic cylinder is:

[0032] k hx =inv(L)*k q *inv(W)

[0033] In the formula, k q is the joint stiffness matrix, and inv() means inverting the matrix.

[0034] Preferably, step S4 specifically includes the following sub-steps:

[0035] S41. The mapping relationship between the foot end of the leg and the equivalent stiffness of the hydraulic cylinder is expressed as:

[0036] k hx =inv(L)*(J T K slip J+K g )*inv(W)

[0037] The specific derivation process is:

[0038] At the joint, there is a relationship between the joint torque and the hydraulic cylinder force:

[0039] τ=LF

[0040] Where, F is the output matrix of the joint hydraulic cylinder;

[0041] in

[0042] F = k hx d xp

[0043] Where, d xp is the minimum change in the generalized position of the hydraulic cylinder;

[0044] The stiffness relationships between the joint torque, hydraulic cylinder output and generalized position are:

[0045] τ=K q (dq)

[0046] F=K hx (dxp)

[0047] Where q is the generalized displacement of the joint;

[0048] The hydraulic cylinder position and the joint position are obtained by derivation of the mapping relationship between the joint angle and the hydraulic cylinder extension. The relationship can be abbreviated as:

[0049] d xp =Wdq;

[0050] The mapping relationship between the minimum change amount of the generalized force of the joint and the minimum change amount of the generalized force of the hydraulic cylinder is expressed as:

[0051] k q (dq) = Lk hx W(dq)

[0052] At the same time, eliminating dq, the mapping relationship between the hydraulic cylinder stiffness of the hydraulically driven leg and the equivalent stiffness of the joint is obtained as follows:

[0053] k hx =inv(L)*k q *inv(W)

[0054] S42. Combined with the mapping relationship between the foot end of the leg and the equivalent stiffness of the joint, the mapping relationship between the foot end of the leg and the equivalent stiffness of the hydraulic cylinder is obtained as follows:

[0055] k hx =inv(L)*(J T K slip J+K g )*inv(W);

[0056] S43, respectively substitute the stiffness mapping relationships between the hydraulic cylinder and the joint, the joint and the foot end, and the foot end and the polar coordinates into the combination:

[0057] k hx =inv(L)*k q *inv(W)

[0058] k q =J T K slip J+K g

[0059] Finally, the relationship between the hydraulic cylinder joint and the spring stiffness of the slip model is:

[0060] k slip =J -T (Lk hx WK g )J -1 .

[0061] Preferably, the specific control method in step S5 is as follows:

[0062] Solve for the total compression Δp of the ground and legs in the z direction z :

[0063]

[0064] The actual height of the hydraulic leg is further solved according to the following formula:

[0065] h z =h0-Δp z

[0066] In the formula, h z is the actual height of the center of mass in the z direction, and h0 is the initial height of the center of mass in the z direction.

[0067] Compared with the prior art, the present invention has the following beneficial effects:

[0068] (1) The variable stiffness control method proposed in the present invention can match a complete set of corresponding relationships to obtain the equivalent SLIP stiffness relationship from the joint to the foot end, which can be used for serial robots with any degree of freedom. Based on the hydraulic leg SLIP model, the flexible control of the robot foot end can be achieved, so that the robot can adapt to a variety of ground environments with different stiffness.

[0069] (2) The present invention can more accurately adjust the stiffness parameters of the hydraulically driven joints by establishing a relationship, realize active variable stiffness control of the joints to adapt to different stiffness environments, and ensure the compliance performance of the robot without making any other improvements to the structure or control of the robot. The entire control process is simple and easy to implement, with low redundancy and high stiffness control accuracy.

[0070] (3) Compared with the traditional method of adding passive springs, the method of the present invention can adapt to various stiffness ground surfaces and does not require the addition of additional passive elastic elements. It has low overall cost and high reliability, and is suitable for large-scale promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 It is a schematic diagram of an equivalent SLIP control model of the hydraulic leg system of the present invention;

[0072] Figure 2 It is a control schematic block diagram of the present invention;

[0073] Figure 3 It is a schematic diagram of the method flow of the present invention;

[0074] Figure 4a-4b 1 is a simulated stiffness curve of an embodiment of the present invention. DETAILED DESCRIPTION

[0075] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0076] The present invention provides a variable stiffness control method for a hydraulic leg SLIP model that can adapt to different stiffness grounds. The method establishes an equivalent model based on a single-leg test experimental platform in actual work to obtain Figure 1 The leg SLIP equivalent model diagram shown is used as an example of a specific expression in the mapping method embodiment.

[0077] like Figure 2 and Figure 3 As shown, the specific implementation steps are as follows:

[0078] S1. Calculate the total stiffness of the ground and the leg in series according to the foot-ground contact force equation, and obtain the leg stiffness in the Cartesian space z direction based on the ground with different stiffness based on the total stiffness in series;

[0079] The foot-ground contact force equation is:

[0080]

[0081] In the formula, f z is the ground contact force in the z direction, K z K is the total stiffness of the ground and legs in series in the z direction, zg is the ground stiffness in the z direction, K zl is the leg stiffness in the z direction, Δp z is the total compression of the ground and legs in the z direction, Δp zg is the ground compression in the z direction, Δp zl is the compression of the leg in the z direction;

[0082] The total series stiffness can be expressed as:

[0083]

[0084] The leg stiffness in the z direction in Cartesian space can be expressed as:

[0085]

[0086] S2. Introduce the SLIP model, establish the relationship between the leg swing angle and radial length of the SLIP model based on the perturbation theory, and obtain the variable stiffness parameters of the SLIP model from the foot end to the center of mass according to the leg stiffness in the z direction of the Cartesian space;

[0087] The relationship between the swing leg angle and radial length of the SLIP model is:

[0088]

[0089] in

[0090] r=r b +acosψ

[0091] Where θ is the swing leg angle of the SLIP model, ε is the perturbation parameter, u0 and u1 are temporary coefficients determined by the initial value, a is the radial vibration amplitude, ψ is the initial phase of the radial vibration, and r b is the radial vibration offset.

[0092] The variable stiffness parameter of the SLIP model from the foot end to the center of mass is:

[0093]

[0094] In the formula, K slip is the variable stiffness parameter of the SLIP model from the foot end to the center of mass.

[0095] S3. According to the mapping relationship between the generalized force of the foot end of the SLIP model and the hydraulic leg joint, and the mapping relationship between the foot end of the SLIP model and the minimum change of the generalized position of the joint, the stiffness relationship between the generalized force and the generalized position of the foot end and the joint is constructed respectively, and the mapping relationship between the foot end of the hydraulic leg and the joint equivalent stiffness is derived to obtain the joint variable stiffness parameter matrix;

[0096] The mapping relationship between the minimum change of generalized force between the foot end and the hydraulic leg joint of the SLIP model is:

[0097] dτ=J T (df)+(dJ T )f

[0098] In the formula, d(·) is the smallest change, (·) T is the transpose of the matrix or vector, τ is the generalized force of the joint, J is the Jacobian matrix from the foot end to the joint of the SLIP model, is the generalized force at the foot end, and its direction is from the foot end to the center of mass;

[0099] Combining stiffness and generalized force, the mapping relationship between the minimum change of the generalized force at the foot end and the joint can be expressed as:

[0100]

[0101] At the same time, eliminate dq to obtain the variable stiffness parameter matrix of the corresponding hydraulic leg joint:

[0102] K q =J T K slip J+K g

[0103] in

[0104]

[0105] S4. Derive the mapping relationship between the equivalent stiffness of each joint of the hydraulic leg and the hydraulic cylinder, and establish the variable stiffness parameters of the hydraulic cylinder of the hydraulic leg SLIP model by combining the joint variable stiffness parameter matrix.

[0106] The mapping relationship between the revolute joint and the equivalent stiffness of the hydraulic cylinder is:

[0107] k hx =inv(L)*k q *inv(W)

[0108] In the formula, k hx is the hydraulic cylinder stiffness matrix, L is the equivalent force arm matrix between the hydraulic cylinder and the joint torque, k q is the joint variable stiffness parameter matrix.

[0109] The mapping relationship between the foot end of the hydraulic leg and the equivalent stiffness of the hydraulic cylinder is:

[0110] k hx =inv(L)*(J T K slip J+K g )*inv(W)

[0111] The specific derivation process is:

[0112] At the joint, there is a relationship between the joint torque and the hydraulic cylinder force:

[0113] τ=LF

[0114] Where, F is the output matrix of the joint hydraulic cylinder;

[0115] in

[0116] F = k hx d xp

[0117] Where, d xp is the minimum change in the generalized position of the hydraulic cylinder;

[0118] The stiffness relationships of joint torque and hydraulic cylinder output and generalized position are:

[0119] τ=K q(dq)

[0120] F=K hx (dxp)

[0121] Where q is the generalized displacement of the joint;

[0122] The hydraulic cylinder position and joint position are obtained by derivation of the mapping relationship between the joint angle and the hydraulic cylinder extension. The relationship can be abbreviated as:

[0123] d xp =Wdq;

[0124] Where W is the length matrix obtained by derivation of the mapping relationship between joint angle and hydraulic cylinder extension.

[0125] The mapping relationship between the minimum change of the generalized force of the joint and the minimum change of the generalized force of the hydraulic cylinder can be expressed as:

[0126] k q (dq) = Lk hx W(dq)

[0127] At the same time, eliminating dq, the mapping relationship between the hydraulic cylinder stiffness of the hydraulically driven leg and the equivalent stiffness of the joint is obtained as follows:

[0128] k hx =inv(L)*k q *inv(W)

[0129] In the formula, k hx is the hydraulic cylinder stiffness matrix, K q is the joint stiffness matrix, L is the equivalent force arm matrix between the hydraulic cylinder and the joint torque, which is determined according to the robot leg structure, and d xp is the minimum change of the generalized position of the hydraulic cylinder, and inv() represents the inversion of the matrix.

[0130] Combined with the mapping relationship between the foot end of the hydraulically driven leg and the equivalent stiffness of the joint, the mapping relationship between the foot end of the hydraulic leg and the equivalent stiffness of the hydraulic cylinder is obtained as follows:

[0131] k hx =inv(L)*(J T K slip J+K g )*inv(W)

[0132] Substitute the stiffness mapping relationships between the hydraulic cylinder and the joint, the joint and the foot end, and the foot end and the polar coordinates into the combination:

[0133] k hx =inv(L)*k q *inv(W)

[0134] k q =JT K slip J+K g

[0135] The relationship between the hydraulic cylinder joint and the slip model stiffness is obtained as follows:

[0136] k slip =J -T (Lk hx WK g )J -1 .

[0137] S5. Combining the variable stiffness parameters of the hydraulic cylinder of the hydraulic leg SLIP model with the environmental variable stiffness parameters, variable stiffness control under different environmental stiffnesses is achieved.

[0138] Based on the equivalent SLIP stiffness obtained by S4, Figure 2 The control method is used to control the hydraulic single leg.

[0139] The schematic diagram of the stiffness mapping method is as follows: Figure 3 shown.

[0140] Figure 4a and Figure 4b This is a schematic diagram of the stiffness mapping stiffness value of this patent. Figure 4a and Figure 4b It can be seen that compared with the traditional control method, the method of the present invention has higher compliance and wider adaptability. In addition, the stiffness mapping method can be further applied to the variable stiffness control of a serial structure robot with more than 6 degrees of freedom. Specific embodiments

[0142] In this embodiment, the control method is applied to Figure 1 In the SLIP model control corresponding to the three-degree-of-freedom hydraulic robot leg shown, the control process is as follows:

[0143] First, the ground stiffness k is obtained by the stiffness identification method. zg , the target robot leg stiffness k is obtained by matching the ground stiffness zl , through the total leg stiffness k zl With k slip The desired leg stiffness is obtained by adjusting the joint impedance control stiffness parameter through the mapping method to obtain the actual leg stiffness k under target control. slip , through the relationship between the foot end contact force and the virtual spring stiffness, the actual height of the slip model is obtained, and the control of the corresponding slip model of the three-degree-of-freedom hydraulic leg is completed, where,

[0144]

[0145] The actual height of the slip model corresponding to the three-degree-of-freedom hydraulic robot leg is:

[0146] h z =h0-Δp z

[0147] In the formula, h z is the height of the center of mass in the z direction, and h0 is the initial height of the center of mass in the z direction.

[0148] The actual height of the slip model corresponding to the three-degree-of-freedom hydraulic robot leg is obtained by solving the above formula, and the three-degree-of-freedom hydraulic robot leg is controlled according to the value of the height. The method of the present invention can be applied to a variety of hydraulically driven robots and has a wide range of application prospects.

[0149] The embodiments described above are only descriptions of the preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A variable stiffness control method for a hydraulic leg SLIP model that can adapt to different stiffness grounds, characterized in that: It includes the following steps: S1. Calculate the total stiffness of the ground and legs in series in the z direction according to the foot-ground contact force equation. Based on the total stiffness in series, obtain the leg stiffness in the z direction under different ground stiffnesses. The specific calculation formula is as follows: Among them, K z K is the total stiffness of the ground and legs in series in the z direction, zg is the ground stiffness in the z direction, K zl is the leg stiffness in z direction; S2. Introduce the SLIP model, establish the relationship between the leg swing angle and the radial length of the SLIP model, and obtain the variable stiffness parameter of the SLIP model from the foot end to the center of mass according to the leg stiffness in the z direction obtained in step S1. The specific expression is as follows: Among them, K slip is the variable stiffness parameter of the SLIP model from the foot end to the center of mass; θ is the leg swing angle of the SLIP model; S3. According to the generalized force mapping relationship between the foot end and the hydraulic leg joint in the SLIP model and the mapping relationship between the foot end and the minimal change of the generalized position of the joint in the SLIP model, the stiffness relationship between the generalized force of the foot end and the joint and the generalized position of the foot end and the joint are constructed respectively, and the equivalent stiffness mapping relationship between the foot end and the joint is obtained to obtain the joint variable stiffness parameters; the joint variable stiffness parameter matrix K q The specific calculation formula is: K q =J T K slip J+K g Where J is the Jacobian matrix from the foot end to the joint of the SLIP model; K q is the joint variable stiffness parameter matrix; To find the derivative, (·) T is the transpose of a matrix or vector, is the generalized force at the foot end, the direction is from the foot end to the center of mass, f z is the foot-ground contact force in the z direction, q is the generalized displacement of the joint; S4, based on the mapping relationship between the equivalent stiffness of each joint of the hydraulic leg and the hydraulic cylinder, combined with the joint variable stiffness parameter K q , establish the variable stiffness parameters of the hydraulic cylinder of the hydraulic leg SLIP model, and the specific calculation formula is: k slip =J -T (Page hx W.K. g )J -1 ; Among them, k hx is the hydraulic cylinder stiffness matrix, L is the equivalent force arm matrix between the hydraulic cylinder and the joint torque, and W is the length matrix obtained by derivation of the mapping relationship between the joint angle and the hydraulic cylinder elongation; S5. Combining the variable stiffness parameters of the hydraulic cylinder of the hydraulic leg SLIP model with the environmental variable stiffness parameters, the actual height of the hydraulic leg is solved to achieve variable stiffness control under different environmental stiffnesses.

2. The variable stiffness control method of the hydraulic leg SLIP model capable of adapting to different stiffness grounds according to claim 1 is characterized in that: The foot-ground contact force equation in step S1 is: In the formula, Δp z is the total compression of the ground and legs in the z direction, Δp zg is the ground compression in the z direction, Δp zl is the compression of the leg in the z direction.

3. The variable stiffness control method of the hydraulic leg SLIP model capable of adapting to different stiffness grounds according to claim 1 is characterized in that: In step S3, the mapping relationship between the minimum change amount of the generalized force between the foot end of the SLIP model and the hydraulic leg joint is: dτ=J T (df)+(dJ T )f In the formula, d(·) is the minimum change, τ is the generalized force of the joint; Combining stiffness and generalized force, the mapping relationship between the minimum change of the foot end and the generalized force of the joint can be expressed as: Where J is the Jacobian matrix, At the same time, eliminate dq to obtain the variable stiffness parameter k corresponding to the hydraulic leg joint q : K q =J T K slip J+K g 。 4. The variable stiffness control method of the hydraulic leg SLIP model capable of adapting to different stiffness grounds according to claim 1 is characterized in that: In step S4, the mapping relationship between the equivalent stiffness of each joint of the hydraulic leg and the hydraulic cylinder is: k hx =inv(L)*k q *inv(W) In the formula, inv() means to invert the matrix.

5. The variable stiffness control method of the hydraulic leg SLIP model capable of adapting to different stiffness grounds according to claim 4 is characterized in that: Step S4 specifically includes the following sub-steps: S41. The mapping relationship between the foot end of the leg and the equivalent stiffness of the hydraulic cylinder is expressed as: k hx =inv(L)*(J T K slip J+K g )*inv(W) The specific derivation process is: At the joint, there is a relationship between the joint torque and the hydraulic cylinder force: τ=LF Where, F is the output matrix of the joint hydraulic cylinder; in F=k hx d xp Where, d xp is the minimum change in the generalized position of the hydraulic cylinder; The stiffness relationships between the joint torque, hydraulic cylinder output and generalized position are: τ=K q (dq) F=K hx (dxp) Where q is the generalized displacement of the joint; The hydraulic cylinder position and the joint position are obtained by derivation of the mapping relationship between the joint angle and the hydraulic cylinder extension. The relationship can be abbreviated as: d xp =Wdq; The mapping relationship between the minimum change amount of the generalized force of the joint and the minimum change amount of the generalized force of the hydraulic cylinder is expressed as: k q (dq)=Lk hx W(dq) At the same time, eliminating dq, the mapping relationship between the hydraulic cylinder stiffness of the hydraulically driven leg and the equivalent stiffness of the joint is obtained as follows: k hx =inv(L)*k q *inv(W) S42. Combined with the mapping relationship between the foot end of the leg and the equivalent stiffness of the joint, the mapping relationship between the foot end of the leg and the equivalent stiffness of the hydraulic cylinder is obtained as follows: k hx =inv(L)*(J T K slip J+K g )*inv(W); S43, respectively substitute the stiffness mapping relationship between the hydraulic cylinder and the joint, and between the joint and the foot end of the slip model into combination: k hx =inv(L)*k q *inv(W) k q =J T K slip J+K g Finally, the relationship between the joint hydraulic cylinder and the spring stiffness of the slip model is: k slip =J -T (Page hx W.K. g )J -1 。 6. The variable stiffness control method of the hydraulic leg SLIP model capable of adapting to different stiffness grounds according to claim 1 is characterized in that: The specific control method in step S5 is as follows: Solve for the total compression Δp of the ground and legs in the z direction z : The actual height of the hydraulic leg is further solved according to the following formula: h z =h0-Δp z In the formula, h z is the height of the center of mass in the z direction, and h0 is the initial height of the center of mass in the z direction.

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