Lightweight design method for bionic robot limbs with honeycomb structure

Abstract

The present invention discloses a lightweight design method for bionic robot limbs with a honeycomb structure, comprising the following steps: S1, determining the basic structural primitive as a regular octagon nested within a regular quadrilateral; S2, determining material property parameters using the mean finite element method; S3, establishing a material performance approximation model using fuzzy neural approximation theory to determine crashworthiness indicators; S4, performing a hierarchical design on the basic structural primitives to obtain the optimal number of levels; S5, performing a gradient design on the basic structural primitives to obtain the optimal gradient distribution. Through the innovative design of regular octagons nested within regular quadrilaterals, the present invention significantly improves the mechanical bearing capacity of the honeycomb structure and solves the problem of easy out-of-plane collapse of thin-walled honeycomb structures.

Description

Technical Field

[0001] The present invention relates to a robot skeleton design, and in particular to a lightweight design method for bionic robot limbs with a honeycomb structure. Background Art

[0002] As a key product of modern technology, bionic robots are widely used in rescue, exploration, military, and service fields. Limb and leg skeleton design is crucial for operating in complex terrain and diverse mission scenarios. Existing technologies typically mimic biological structures, combining mechanical analysis with material optimization to create a skeletal system that combines high strength and flexibility. The design process involves biomorphological research, finite element analysis, and multi-material composite manufacturing to achieve a balance between motion performance and load-bearing capacity.

[0003] However, existing technologies have significant flaws. As bionic robots' missions diversify, their load-bearing requirements have increased significantly, but traditional skeleton designs struggle to achieve lightweighting while maintaining strength. Excessively heavy skeletons not only limit the robot's maneuverability and endurance, but also increase energy consumption and joint loads, impacting overall performance. Furthermore, current design methods lack innovation in material selection and structural optimization, further limiting the potential for lightweighting breakthroughs. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for designing lightweight bionic robot limbs with a honeycomb structure by optimizing the structure of the skeletal unit to achieve the purpose of lightweighting the bionic robot limbs.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A lightweight design method for bionic robot limbs with a honeycomb structure is carried out according to the following steps:

[0006] S1, determining a basic structural primitive, wherein the basic structural primitive is a regular octagon and a regular quadrilateral nested outside the regular octagon;

[0007] S2, determine the material property parameters by the mean value finite element method;

[0008] S3, establishes a material performance approximation model through fuzzy neural approximation theory to determine the crashworthiness index;

[0009] S4, perform hierarchical design on the basic structural primitives to obtain the optimal solution for the number of levels;

[0010] S5, performing gradient design on the basic structural primitives after step S4 to obtain the optimal gradient distribution.

[0011] Furthermore, the hierarchical design is performed according to the following steps:

[0012] S41, repeating the S1-S2 process with the number of levels to build a model library;

[0013] S42, obtaining a hierarchical optimal solution in the model library in step S41 by using an adaptive mutation particle swarm method;

[0014] S43, re-determine the basic structural primitives based on the hierarchical optimal solution obtained in step S42.

[0015] Furthermore, the gradient design includes relative density gradient design and size gradient design. The relative density gradient design refers to the distribution of the basic structural element on the plane obtained in step S43; the size gradient design refers to the size and wall thickness of the basic structural element obtained in step S43.

[0016] Furthermore, the relative density gradient design and size gradient design are carried out according to the following steps:

[0017] S51, using the number of levels obtained in step S43 as the initial gradient number;

[0018] S52, establishing a topology optimization mathematical model through the initial gradient number in step S51 and obtaining the gradient optimal solution through the topology optimization design method.

[0019] Furthermore, in the step S52, the topology optimization design method starts from the initial gradient number, gradually decreases to the first level, and then reverses from the first level back to the initial gradient number to iterate repeatedly.

[0020] Furthermore, it also includes a reinforcing structural element, wherein the reinforcing structural element is provided with a reinforcing block in the form of a regular quadrilateral at the center of the basic structural element, and the reinforcing block is connected to the center of the hypotenuse of the regular octagon in the basic structural element at its four corners to form a connecting plate.

[0021] Furthermore, the reinforcement blocks in the reinforcement structural element can be mounted on the basic structural element.

[0022] The beneficial effects of the present invention are as follows:

[0023] First, through the innovative design of a basic structural element consisting of regular octagons nested within regular quadrilaterals, the mechanical bearing capacity of the honeycomb structure has been effectively improved. Experimental data shows that the in-plane equivalent elastic modulus of this combined honeycomb-like sandwich structure is approximately 20 times higher than that of traditional honeycomb-like structures, resolving the industry challenge of out-of-plane collapse of thin-walled honeycomb structures. The triangular support system formed by the nested structure strengthens the in-plane stiffness, achieving a breakthrough increase in longitudinal bearing capacity at the same density, providing a reliable structural foundation for lightweighting the robot's limbs.

[0024] Second, a collaborative optimization strategy of hierarchical and gradient factors was employed to achieve a multi-dimensional match between material properties and structural parameters. This dual composite optimization mechanism overcomes the limitations of traditional single-scale design, enabling the honeycomb structure to exhibit controllable progressive crushing characteristics under dynamic loads.

[0025] Third, an integrated structure-material-function design system was constructed, significantly improving engineering applicability. By establishing a mathematical model library encompassing geometric characteristic parameters, material constitutive relationships, and functional indicators, and incorporating fuzzy neural approximation theory, rapid multi-objective optimization was achieved. This system can be directly applied to bionic robot joints, achieving weight reduction while maintaining structural integrity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a flowchart of steps of an embodiment of the present invention;

[0027] Figure 2 A plan view of a basic structural element of an embodiment of the present invention;

[0028] Figure 3 A plan view of a structural primitive for strengthening an embodiment of the present invention;

[0029] Figure 4 This is a flow chart of the numerical simulation and experimental testing scheme of an embodiment of the present invention;

[0030] Figure 5 This is a design flow chart for an embodiment of the present invention applied to a bionic robot limb;

[0031] Figure 6 1 is the structure calculated and optimized under a certain load-bearing capacity according to an embodiment of the present invention (the dotted line portion is the research object of the mechanical parameters);

[0032] Figure 7 for Figure 6 Force analysis diagram of the structure in the x direction;

[0033] Figure 8 for Figure 6 Force analysis diagram of the middle structure in the y direction;

[0034] Figure 9 for Figure 6 Stress-strain curves of the samples obtained from the structure measured in quasi-static compression;

[0035] Figure 10 for Figure 6 Displacement cloud diagram of the structural numerical model (where a is the horizontal displacement cloud diagram under normal stress in the x direction; b is the vertical displacement cloud diagram under normal stress in the x direction; c is the horizontal displacement cloud diagram under normal stress in the y direction; d is the vertical displacement cloud diagram under normal stress in the y direction). DETAILED DESCRIPTION

[0036] The embodiment of the present invention provides a lightweight design method for bionic robot limbs with a honeycomb structure. Figure 1-10 As shown:

[0037] The specific operation process is as follows:

[0038] S1, determine the basic structural primitives or reinforced structural primitives.

[0039] The basic structural primitives include a regular octagon and a regular quadrilateral nested outside the regular octagon.

[0040] The reinforcement element is equipped with a square-shaped reinforcement block at the center of the base element. The reinforcement block is connected to the center of the hypotenuse of the regular octagon in the base element at its four corners to form a connecting plate. In addition, the reinforcement block in the reinforcement element can also be placed inside the base element.

[0041] The design of the basic structural element is inspired by the honeycomb structure in nature. It has high specific strength and specific stiffness, and can effectively achieve the goal of lightweighting.

[0042] The reinforced structural element further enhances the overall strength and crashworthiness of the structure by adding a regular quadrilateral reinforcement block at the center of the basic structural element. The connecting plate between the reinforcement block and the regular octagon acts as a force transmitter to avoid stress concentration.

[0043] The design that the reinforcement blocks can be fitted onto the basic structural elements makes the overall structure more flexible and facilitates adjustment of the position and number of the reinforcement blocks according to actual needs.

[0044] S2, determine the material property parameters by the mean value finite element method.

[0045] The mean value finite element method is used to analyze the basic structural elements to determine key material property parameters such as elastic modulus, Poisson's ratio, density, etc. These parameters provide data support for the subsequent establishment of an approximate model of material properties.

[0046] The mean value finite element method calculates the mechanical response of the material under different working conditions by discretizing the geometric shape and boundary conditions of the structural elements.

[0047] The key to this step is to ensure the accuracy and convergence of the finite element model so that it accurately reflects the actual performance of the material.

[0048] S3, establishes a material performance approximation model through fuzzy neural approximation theory to determine the crashworthiness index.

[0049] Based on the fuzzy neural network algorithm and combined with the material property parameters obtained in step S2, an approximate material performance model is established to evaluate the crashworthiness index of the structure.

[0050] Fuzzy neural networks combine the uncertainty of fuzzy logic and the learning ability of neural networks, and can effectively handle complex nonlinear problems.

[0051] Crashworthiness indicators include but are not limited to impact energy absorption rate, maximum deformation, etc., which are used to measure the performance of the structure during a collision.

[0052] S4, hierarchical design of basic structural primitives;

[0053] The steps include:

[0054] S41: Repeat the S1-S2 process by changing the number of levels to build a model library.

[0055] By adjusting the number of layers (such as single layer, double layer or multi-layer), the geometric model of the basic structural element is regenerated, and the material property parameters of each model are calculated using the mean finite element method to form a model library.

[0056] S42: Obtain the hierarchical optimal solution in the model library in step S41 through the adaptive mutation particle swarm method.

[0057] Adaptive mutation particle swarm optimization is an efficient global optimization algorithm that can quickly search the model library for the optimal number of levels that meets performance requirements.

[0058] S43: Re-determine the basic structural primitives based on the hierarchical optimal solution obtained in step S42.

[0059] According to the optimal number of levels, the geometric parameters of the basic structural primitives are updated to lay the foundation for subsequent gradient design.

[0060] The core of hierarchical design is to balance the lightweight and mechanical properties of the structure by increasing or decreasing the number of layers.

[0061] The adaptive mutation particle swarm algorithm avoids falling into the local optimal solution by dynamically adjusting the particle position and speed, thereby improving the optimization efficiency.

[0062] S5: Perform gradient design on the basic structural elements after step S4.

[0063] The gradient design includes relative density gradient design and size gradient design:

[0064] Relative density gradient design refers to the distribution of the basic structural elements on the plane obtained in step S43;

[0065] Size gradient design refers to the basic structural element size and wall thickness obtained in step S43.

[0066] The steps include:

[0067] S51: The number of levels obtained in step S43 is used as the initial gradient number.

[0068] The optimal number of levels is used as the initial gradient number to define the starting point of the gradient design.

[0069] S52: A topology optimization mathematical model is established based on the initial gradient number in step S51, and the gradient optimal solution is obtained through the topology optimization design method.

[0070] The topology optimization design method searches for the optimal gradient distribution scheme through step-by-step iteration (starting from the initial gradient number, stepping down to level 1, and then returning from level 1 to the initial gradient number).

[0071] Gradient design aims to adjust the relative density and size distribution so that the structure has different mechanical properties in different areas, thereby better adapting to complex load environments.

[0072] The topology optimization method uses repeated iterations to ensure that the final design solution meets the performance requirements while achieving the lightweight goal.

[0073] After determining the hierarchy and gradient, the resulting structure is as follows Figure 6 As shown, the following is the calculation of its in-plane equivalent mechanical parameters:

[0074] The equivalent mechanical parameters of the composite honeycomb sandwich structure are derived using Hooke's theorem and classical beam bending theory. Figure 6 The unit body inside the dotted line is taken as the research object, and the force analysis on the x-axis and y-axis is performed on it. Its structural dimensions are as follows Figure 6 As shown in the figure, a represents the side length of the octagon; l represents the height of the sandwich cell wall; t represents the thickness of the octagon cell; t1 and t2 represent the thickness of different quadrilateral cell walls; H1 represents the initial length of the unit cell along the x direction; H2 represents the initial length of the unit cell along the y direction; θ represents the angle between the side length of the octagon and the transverse direction.

[0075] The derivation process of the equivalent elastic modulus in the x direction is as follows:

[0076] The force of the tensile structure in the x direction is as follows Figure 6 As shown in the figure, the unit cell structure taken out from the square is symmetrical, and the stress conditions and constraints are the same, so it is simplified into a 1 / 2 model as the research object for deriving the equivalent elastic constants of the combined honeycomb-like structure. The simplified structure is subjected to stress in the x direction as follows Figure 7 As shown, according to the force conditions, calculate their l xAB Rod, l xAC Rod and l xAD The force P on the rod x0 、P x2 and P x1 According to the classical beam bending theory, the deformation of each rod is calculated.

[0077] Depend on Figure 4 The geometric size relationship can be obtained

[0078] H1=(2cosθ+1)a+t1 (1)

[0079] H2=(2sinθ+1)a+t2 (2)

[0080] Will l xAE After the rod section is broken, the rod l xAB The actual length is

[0081] lxAB=a-(2cosθ-1)t (3)

[0082] Depend on Figure 5 As shown, the force analysis of point A can be obtained

[0083] ∑Fx=Px2+2Px1cosθ-Px=0 (4)

[0084] ∑Fy=Px1sinθ-Px0cosθ=0 (5)

[0085] Coordination equations

[0086] △lxAB=△lxACcosθ (6)

[0087] The solution is

[0088]

[0089] where l xAB Rod and l xAC Cross-sectional area of ​​the rod A xAB and A xAC They are

[0090] A xAB =tl (8)

[0091] A xAC =t2l (9)

[0092] Under external force P x Under the effect of xCE The deformation of the rod is

[0093]

[0094] Where E s is the collective material elastic modulus.

[0095] l xCE The total axial deformation of the rod is

[0096] Δl xCE =ΔlxAC +Δl xAE (12)

[0097] Under external force P x Under the effect of xAB The deformation of the rod is

[0098]

[0099] The equivalent effect in the x-direction becomes

[0100]

[0101] Similarly, the equal strain in the y direction can be obtained as

[0102]

[0103] According to the definition of Poisson's ratio, the equivalent Poisson's ratio of the combined honeycomb-like sandwich structure in the x direction can be obtained from equations (10), (11) and (13):

[0104]

[0105] The external force at the sandwich cell node is

[0106] Px=σcxH2l=σcx[(2sinθ+1)a+t2]l (17)

[0107] According to the definition of elastic modulus, we can get Figure 6 The equivalent elastic modulus of the structure shown in the x direction is

[0108]

[0109] The derivation process of the equivalent elastic modulus in the y direction is as follows:

[0110] The force on the tensile structure in the y direction is as follows Figure 6 As shown in the figure, since it satisfies the structural symmetry, the force conditions and the constraint conditions, it is simplified into a 1 / 2 model as the research object in the y direction. The simplified structure is subjected to force in the y direction as shown in the figure. Figure 8 As shown, according to the force conditions, calculate their l yAB Rod, l yAC Rod and l yAD The force on the rod, then calculate the deformation of each rod, and finally calculate the equivalent elastic constant E cy .

[0111] Force analysis of point B yields

[0112] ∑Fx=Py0cosθ-Py1cosθ=0 (19)

[0113] ∑Fy=Py2+2Py1sinθ-Py=0 (20)

[0114] Coordination equations

[0115] △lyAB=△lyBCsinθ (21)

[0116] The solution is

[0117]

[0118] where l yAB Rod and l yBC The cross-sectional areas of the rods are

[0119] AyAB=th (23)

[0120] AyCB=t1h (24)

[0121] Under external force P y Under the effect of yCE The deformation of the rod is

[0122]

[0123] Where E s is the collective material elastic modulus.

[0124] l yCE The total axial deformation of the rod in the y direction is

[0125] Δl yCE =Δl yCA +Δl yAE (27)

[0126] l yAB The deformation of the rod under the action of external force is

[0127]

[0128] The total deformation in the y direction is

[0129] Δl y =Δl yCA +Δl yCE +Δl yAB sinθ (29)

[0130] Similarly, the equal strain in the y direction can be obtained as

[0131]

[0132] According to Hu Ke's theorem, the equivalent strain in the y direction is obtained

[0133]

[0134] According to the definition of Poisson's ratio, the equivalent Poisson's ratio of the combined honeycomb-like sandwich structure in the y direction is:

[0135]

[0136] The external force at the sandwich cell node is

[0137] Py=σcyH1l=σcy[(2cosθ+1)a+t1]l (33)

[0138] According to the definition of elastic modulus, we can get Figure 6 The equivalent elastic modulus of the structure shown in the y direction is

[0139]

[0140] right Figure 6 The structure shown is verified by quasi-static compression test, and the process is as follows:

[0141] The quasi-static compression test is a common experimental test in mechanical property research. The lower plate is fixed to the experimental sample, and the upper pressure head is used to axially compress the experimental sample. When the compression rate is constant, the sample deforms in the axial direction. The sensor transmits the data measured during the compression process to the system to obtain the experimental results. Before conducting the experiment, the experimental plan is designed first. The experimental mode is selected as: plastic compression test. The pressure head axially loads the combined honeycomb sandwich structure, and the compression loading rate is set to 1mm / min. During the experiment, the computer collects data and controls the process in real time.

[0142] This application uses 3D printing technology to produce a composite honeycomb sandwich multi-cellular structure sample. The material used is PLA material with good mechanical and physical properties, and its density is 1180kg / m 3 , Poisson's ratio is 0.03, tensile strength is 60MPa, and elastic modulus is 1833MPa.

[0143] The sample dimensions of the combined honeycomb-like sandwich structure are: t = t1 = t2 = 0.8 mm, l = 10 mm, a = 8 mm. A quasi-static compression test was performed on the combined honeycomb-like sandwich structure to obtain the experimental elastic modulus.

[0144] according to Figure 9 It can be seen that the combined honeycomb-like sandwich structure made of PLA material experienced an elastic stage and a plastic deformation stage during the quasi-static compression process. As the sample was compressed more and more flat, the cross-sectional area increased, so the compressive capacity of the sample increased accordingly, and the curve stress increased again.

[0145] Since the combined honeycomb-like sandwich structure has a symmetrical structure when the quadrilateral protective wall and the octagonal protective wall have the same thickness, only the quasi-static compression test was performed on it in the x-direction. According to the measured experimental data, the experimental value of the equivalent elastic modulus of the combined honeycomb-like sandwich structure in the y-direction is 103.57 MPa, and the error between it and the theoretical value of 120.24 MPa obtained by formula (34) is 13.86%. The error is within the allowable range, verifying the correctness of the theoretical formula. The main reasons for the error between the experimental value and the theoretical value measured in the quasi-static compression test are: ① The simplified equivalent model extracted from the multi-element model is used in the theoretical derivation; ② The error caused by human factors during the experiment and the error caused by the machine itself; ③ Since the 3D printer uses a molten deposition method, there are tiny gaps in the sample that are invisible to the naked eye, and the processed sample is not a homogeneous material under ideal conditions, which leads to errors.

[0146] In order to verify the correctness of the theoretical derivation formula mentioned above, the Abaqus simulation software was used to perform numerical simulation on the combined honeycomb-like sandwich structure. A numerical model of the combined honeycomb-like sandwich structure was established, and its size was consistent with the size of the processed sample. The material properties were assigned: elastic modulus of 1833MPa, Poisson's ratio of 0.03, and density of 1180kg / m3. In order to make the model uniformly stressed and reduce errors, a rigid plate was bound to the combined honeycomb-like quadruple sandwich structure. A pressure of 6MPa was applied to the steel plate to completely constrain the bottom surface of the combined honeycomb-like sandwich structure. The displacement cloud diagram after being subjected to positive stress in the r direction and the 1 direction is shown as follows: Figure 10 In the figure, U1 and U2 respectively represent the displacement of the model in the horizontal and vertical directions after the force is applied.

[0147] The comparison of equivalent parameters of the combined honeycomb-like sandwich structure is shown in the following table. It can be seen that the simulation analysis conclusions are basically consistent with the theoretical calculation values. The error of the equivalent elastic modulus is about 10.60%, and the error of Poisson's ratio is 5.03%, which further verifies the correctness of the equivalent mechanical parameters of the combined honeycomb-like sandwich structure.

[0148]

[0149] Comparison of equivalent parameters of combined honeycomb sandwich structures

[0150] The above embodiment is only one of the preferred specific implementations of the present invention. Those skilled in the art may make appropriate adjustments or improvements to each step according to actual needs. For example, the shape of the basic structural element may be replaced with other polygons, or a different optimization algorithm may be used instead of the adaptive mutation particle swarm optimization method.

Claims

1. A lightweight design method for bionic robot limbs with a honeycomb structure is carried out according to the following steps: S1, determining a basic structural primitive, wherein the basic structural primitive is a regular octagon and a regular quadrilateral nested outside the regular octagon, and further comprising a reinforcement structural primitive, wherein the reinforcement structural primitive has a regular quadrilateral reinforcement block provided at the center of the basic structural primitive, and the reinforcement block is connected at its four corners to the center of the hypotenuse of the regular octagon in the basic structural primitive to form a connecting plate; S2, determine the material property parameters by the mean value finite element method; S3, establishes a material performance approximation model through fuzzy neural approximation theory to determine the crashworthiness index; S4, perform hierarchical design on the basic structural primitives to obtain the optimal solution for the number of levels; S5, performing gradient design on the basic structural primitives after step S4 to obtain the optimal gradient distribution.

2. The lightweight design method for bionic robot limbs with a honeycomb structure according to claim 1, characterized in that: The hierarchical design is carried out according to the following steps: S41, repeating the S1-S2 process with the number of levels to build a model library; S42, obtaining a hierarchical optimal solution in the model library in step S41 by using an adaptive mutation particle swarm method; S43, re-determine the basic structural primitives based on the hierarchical optimal solution obtained in step S42.

3. The lightweight design method for bionic robot limbs with a honeycomb structure according to claim 2, characterized in that: The gradient design includes relative density gradient design and size gradient design. The relative density gradient design refers to the distribution of the basic structural elements on the plane obtained in step S43; the size gradient design refers to the size and wall thickness of the basic structural elements obtained in step S43.

4. The lightweight design method for bionic robot limbs with a honeycomb structure according to claim 3 is characterized by: The relative density gradient design and size gradient design are carried out according to the following steps: S51, using the number of levels obtained in step S43 as the initial gradient number; S52, establishing a topology optimization mathematical model through the initial gradient number in step S51 and obtaining the gradient optimal solution through the topology optimization design method.

5. The lightweight design method for bionic robot limbs with a honeycomb structure according to claim 4 is characterized in that: In the step S52, the topology optimization design method starts from the initial gradient number, gradually decreases to the first level, and then reverses from the first level back to the initial gradient number and iterates repeatedly.

6. The lightweight design method for bionic robot limbs with a honeycomb structure according to claim 1, characterized in that: The reinforcement blocks in the reinforcement structural element can be nested on the basic structural element.

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