Lightweight design method for limbs and legs of bionic robot with honeycomb structure

Abstract

The invention discloses a lightweight design method for limbs and legs of a bionic robot with a honeycomb structure. The lightweight design method comprises the following steps: S1, determining that basic structure elements are regular octagons nested with regular quadrangles; s2, determining material attribute parameters through a mean value finite element method; s3, establishing a material performance approximation model by using a fuzzy neural approximation theory to determine a crashworthiness index; s4, performing hierarchical design on the basic structure elements to obtain an optimal hierarchical number; and S5, carrying out gradient design on the basic structure elements to obtain optimal gradient distribution. Through the innovative design that the regular octagon is nested in the regular quadrangle, the mechanical bearing performance of the honeycomb structure is remarkably improved, and the problem that the thin-wall honeycomb structure is prone to collapse outside the plane is solved.

Description

Technical Field

[0001] The 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 an important product of modern science and technology, bionic robots are widely used in rescue, exploration, military and service fields. In complex terrain and diverse mission scenarios, the design of limb bones becomes a key link. Existing technologies usually simulate biological structures and combine mechanical analysis with material optimization to build a skeletal system with high strength and flexibility. The design process involves steps such as 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 obvious defects. With the diversification of bionic robot tasks, their load-bearing requirements have increased significantly, but traditional skeleton design is difficult to achieve lightweight while ensuring strength. Overweight skeletons not only limit the robot's maneuverability and endurance, but also increase energy consumption and joint loads, affecting overall performance. In addition, the current design method lacks innovation in material selection and structural optimization, further restricting the possibility of lightweight breakthroughs. Summary of the invention

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

[0005] To achieve the above object, 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: S1, determining a basic structural primitive, wherein the basic structural unit is a regular octagon and a regular quadrilateral nested outside the regular octagon; S2, determine the material property parameters by the mean value finite element method; S3, establish the 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 hierarchical levels; S5, performing gradient design on the basic structural primitives after step S4 to obtain the optimal gradient distribution.

[0006] Furthermore, the hierarchical design is performed according to the following steps: S41, repeating the S1-S2 process with changing the number of levels to establish 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, redetermine the basic structural primitives using the hierarchical optimal solution obtained in step S42.

[0007] 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.

[0008] Further, the relative density gradient design and size gradient design are carried out according to the following steps: S51, taking 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.

[0009] Furthermore, in the step S52, the topology optimization design method starts from an 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.

[0010] 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 unit, and the reinforcing block is connected at its four corners to the center of the hypotenuse of the regular octagon in the basic structural unit to form a connecting plate.

[0011] Furthermore, the reinforcement blocks in the reinforcement structure unit can be sleeved on the basic structure unit.

[0012] The beneficial effects of the present invention are as follows: First, the mechanical bearing capacity of the honeycomb structure is effectively improved through the innovative design of the basic structural element of regular octagons nested in regular quadrilaterals. Experimental data show that the in-plane equivalent elastic modulus of this combined honeycomb-like sandwich structure is about 20 times higher than that of the traditional honeycomb-like structure, solving the industry problem of the easy collapse of thin-walled honeycomb structures out of the plane. The triangular support system formed by the nested structure strengthens the in-plane stiffness, achieving a breakthrough improvement in the longitudinal bearing capacity at the same density, and providing a reliable structural foundation for the lightweighting of robot limbs.

[0013] Second, the hierarchical factor and gradient factor synergistic optimization strategy is adopted to achieve multi-dimensional matching of material properties and structural parameters. This dual composite optimization mechanism breaks through the limitations of traditional single-scale design and enables the honeycomb structure to present controllable progressive crushing characteristics under dynamic loads.

[0014] Third, a structure-material-function integrated design system was constructed, which significantly improved the engineering applicability. By establishing a mathematical model library covering geometric characteristic parameters, material constitutive relations and functional indicators, multi-objective rapid optimization was achieved by combining fuzzy neural approximation theory. This system can be directly applied to bionic robot joints to achieve weight reduction while maintaining structural integrity. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a flowchart of steps of an embodiment of the present invention; Figure 2 A plan view of a basic structural element of an embodiment of the present invention; Figure 3 A plan view of a structural primitive for strengthening an embodiment of the present invention; Figure 4 It is a flow chart of numerical simulation and experimental test scheme of the embodiment of the present invention; Figure 5 This is a design flow chart of an embodiment of the present invention applied to a bionic robot limb; Figure 6 The structure after calculation and optimization under a certain load-bearing capacity of the embodiment of the present invention (the dotted line part is the research object of the mechanical parameters); Figure 7 for Figure 6 Force analysis diagram of the structure in the x direction; Figure 8 for Figure 6 Force analysis diagram of the middle structure in the y direction; Fig. 9 for Figure 6 Stress-strain curves of the samples obtained from the structure measured in quasi-static compression; Fig.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

[0016] A method for lightweight design of bionic robot limbs with a honeycomb structure according to an embodiment of the present invention is as follows Figure 1-10 As shown: The specific operation process is as follows: S1, determine the basic structural primitives or reinforced structural primitives.

[0017] The basic structural primitives include a regular octagon and a regular quadrilateral nested outside the regular octagon.

[0018] The reinforcement structure primitive is provided with a regular quadrilateral reinforcement block at the center of the basic structure unit, and the reinforcement block is connected to the center of the regular octagonal hypotenuse in the basic structure unit from its four corners to form a connecting plate. In addition, the reinforcement block in the reinforcement structure unit can also be sleeved with the basic structure unit.

[0019] 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.

[0020] The reinforced structural unit further improves the overall strength and crash resistance of the structure by adding a regular quadrilateral reinforcement block at the center of the basic structural unit. The connecting plate between the reinforcement block and the regular octagon plays a role in force transmission and avoids stress concentration.

[0021] The design that the reinforcement blocks can be mounted on the basic structural unit makes the overall structure more flexible and facilitates adjustment of the position and number of the reinforcement blocks according to actual needs.

[0022] S2, determine the material property parameters by the mean value finite element method.

[0023] The basic structural elements are analyzed using the mean finite element method to determine key property parameters such as the elastic modulus, Poisson's ratio, density, etc. These parameters provide data support for the subsequent establishment of an approximate model for material performance.

[0024] The mean 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 element.

[0025] 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.

[0026] S3, establishes a material performance approximation model through fuzzy neural approximation theory to determine the crashworthiness index.

[0027] 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.

[0028] Fuzzy neural networks combine the uncertainty of fuzzy logic and the learning ability of neural networks, and can effectively handle complex nonlinear problems.

[0029] 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.

[0030] S4, hierarchical design of basic structural primitives; The steps include: S41: Repeat the S1-S2 process by changing the number of levels to build a model library.

[0031] 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.

[0032] S42: Obtain the hierarchical optimal solution in the model library in step S41 through the adaptive mutation particle swarm method.

[0033] The adaptive mutation particle swarm algorithm is an efficient global optimization algorithm that can quickly search for the optimal number of levels that meets performance requirements in the model library.

[0034] S43: Redetermine the basic structural primitives based on the hierarchical optimal solution obtained in step S42.

[0035] 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.

[0036] The core of layer design is to balance the lightweight and mechanical properties of the structure by increasing or decreasing the number of layers.

[0037] The adaptive mutation particle swarm algorithm avoids falling into the local optimal solution by dynamically adjusting the position and speed of particles, thereby improving the optimization efficiency.

[0038] S5: Perform gradient design on the basic structural elements after step S4.

[0039] 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 primitives on the plane obtained in step S43; Size gradient design refers to the size and wall thickness of the basic structural element obtained in step S43.

[0040] The steps include: S51: The number of levels obtained in step S43 is used as the initial gradient number.

[0041] The optimal number of levels is used as the initial gradient number to define the starting point of the gradient design.

[0042] S52: A topology optimization mathematical model is established through the initial gradient number in step S51, and the gradient optimal solution is obtained through the topology optimization design method.

[0043] 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).

[0044] Gradient design aims to make the structure have different mechanical properties in different areas by adjusting the relative density and size distribution, so as to better adapt to the complex load environment.

[0045] The topology optimization method uses repeated iterations to ensure that the final design solution meets the performance requirements while achieving the lightweight goal.

[0046] After determining the hierarchy and gradient, the resulting structure is as follows Figure 6 As shown, the following is to calculate its in-plane equivalent mechanical parameters: The equivalent mechanical parameters of the composite honeycomb sandwich structure are derived by 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, a represents the side length of the octagon; l represents the height of the sandwich cell wall; t represents the thickness of the octagonal 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.

[0047] The derivation process of the equivalent elastic modulus in the x direction is as follows: The force of the tensile structure in the x direction is Figure 6 As shown in the figure, the unit cell structure taken out from the square is symmetrical, and the force conditions and constraints are the same, so it is simplified into a 1 / 2 model as the research object for deriving equivalent elastic constants of combined honeycomb-like structures. The simplified structure is subjected to force 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 on the rod is P x0 , P x2 and P x1 According to the classical beam bending theory, the deformation of each rod is calculated.

[0048] Depend on Figure 4 The geometric size relationship can be obtained (1) (2) Will l xAE After the rod section is broken, the rod l xAB The actual length is (3) Depend on Figure 5 As shown in the figure, the force analysis of point A yields (4) (5) Coordination equation (6) Solved (7) Among them l xAB Rod and l xAC The cross-sectional area of ​​the rod is A xAB and A xAC They are A xAB =tl (8) A xAC =t2l (9) In the external force P x Under the effect xCE The deformation of the rod is (10) (11) Where E s is the collective material elastic modulus.

[0049] l xCE The total axial deformation of the rod is (12) In the external force P x Under the effect xAB The deformation of the rod is (13) The equivalent effect in the x direction becomes (14) Similarly, the equal strain in the y direction can be obtained as (15) 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): (16) The external force at the sandwich cell node is (17) 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 (18) The derivation process of the equivalent elastic modulus in the y direction is as follows: The force on the tensile structure in the y direction is as follows Figure 6As shown in the figure, since it satisfies the structural symmetry, the force conditions and the constraint conditions are symmetrical, 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 .

[0050] The force analysis of point B gives Coordination equation (twenty one) Solved (twenty two) Among them l yAB Rod and l yBC The cross-sectional areas of the rods are In the external force P y Under the effect yCE The deformation of the rod is (25) (26) Where E s is the collective material elastic modulus.

[0051] l yCE The total axial deformation of the rod in the y direction is (27) l yAB The deformation of the rod under the action of external force is (28) The total deformation in the y direction is (29) Similarly, the equal strain in the y direction can be obtained as (30) According to Hu Ke's theorem, the equivalent strain in the y direction is obtained (31) 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: (32) The external force at the sandwich cell node is 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 (34) right Figure 6 The structure shown is verified by quasi-static compression experiment, and the process is as follows: 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 compress the experimental sample axially. 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.

[0052] This application uses 3D printing technology to produce a combined honeycomb-like sandwich multi-cell structure sample. The material uses PLA material with good mechanical and physical properties, with a density of 1180kg / m³, a Poisson's ratio of 0.03, a tensile strength of 60MPa, and an elastic modulus of 1833MPa.

[0053] The sample size of the combined honeycomb-like sandwich structure is: t=t1=t2=0.8mm, l=10mm, a=8mm. A quasi-static compression test is performed on the combined honeycomb-like sandwich structure to obtain the experimental elastic modulus.

[0054] according to Fig. 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. When 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.

[0055] Since the thickness of the quadrilateral protective wall and the octagon of the combined honeycomb sandwich structure is the same, it is a symmetrical structure. Therefore, only the quasi-static compression test was carried out on it in the x direction. According to the measured experimental data, the experimental value of the equivalent elastic modulus of the combined honeycomb sandwich structure in the y direction is 103.57MPa, and the error between it and the theoretical value of 120.24MPa obtained by formula (34) is 13.86%. The error is within the allowable range, which verifies 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-cell 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 adopts the method of molten deposition, 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.

[0056] In order to verify the correctness of the above theoretical derivation formula, 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 evenly 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 a, r, and 1 directions is shown as follows. Fig.10 As shown in the figure, U1 and U2 respectively represent the displacement of the model in the horizontal direction and vertical direction after being subjected to force.

[0057] The comparison of equivalent parameters of the combined honeycomb-like sandwich structure is shown in the following table. It can be obtained 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.

[0058]

[0059] Comparison of equivalent parameters of combined honeycomb sandwich structures The above embodiment is only one of the preferred specific implementations of the present invention, and those skilled in the art can make appropriate adjustments or improvements to each step according to actual needs. For example, the shape of the basic structural primitive can be replaced by other polygons, or a different optimization algorithm can be used to replace the adaptive mutation particle swarm 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 unit is a regular octagon and a regular quadrilateral nested outside the regular octagon; S2, determine the material property parameters by the mean value finite element method; S3, establish the 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 hierarchical 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 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 changing the number of levels to establish 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, redetermine the basic structural primitives using the hierarchical optimal solution obtained in step S42.

3. The lightweight design method for bionic robot limbs with 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 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.

4. The lightweight design method for bionic robot limbs with honeycomb structure according to claim 3 is characterized in that: The relative density gradient design and size gradient design are carried out according to the following steps: S51, taking 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 honeycomb structure according to claim 4, characterized in that: In the step S52, the topology optimization design method starts from the initial gradient number, gradually goes down 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 any one of claims 1 to 5, characterized in that: It also includes a reinforcing structural unit, wherein a reinforcing block in the shape of a regular quadrilateral is arranged at the center of the basic structural unit, and the reinforcing block is connected at its four corners to the center of the hypotenuse of the regular octagon in the basic structural unit to form a connecting plate.

7. The lightweight design method for bionic robot limbs with honeycomb structure according to claim 6, characterized in that: The reinforcement blocks in the reinforcement structure unit can be sleeved on the basic structure unit.

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