Mechanical finger structure based on additive manufacturing

Abstract

According to the assembly-free mechanical finger structure based on additive manufacturing, near-end knuckles and far-end knuckles are filled with variable-density diamond lattices to form a light-weight framework, metacarpophalangeal joints are arranged at the joints of the near-end knuckles and a palm, flexible interphalangeal joints are integrally arranged at the joints of the near-end knuckles and the far-end knuckles, and the flexible interphalangeal joints are connected with the near-end knuckles. The flexible interphalangeal joint comprises a plurality of thin-wall joint layers which are integrally formed and arranged in parallel, the thin-wall joint layers are coaxially arranged through a mandrel fixed between the thin-wall joint layers, Archimedes spiral groove holes are reserved in the thin-wall joint layers with the mandrel as the circle center, and the thin-wall joint layers form an Archimedes spiral blade with an outer wall. The mechanical finger structure is provided with an integrated flexible joint structure, the machining process is simple, the machining period is short, the cost is low, and the mechanical finger structure is particularly suitable for occasions where relative rotation is small, the number of working cycle times is small, and certain rebound resilience is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of robotic arm equipment, and specifically relates to a robotic finger structure based on additive manufacturing. Background Art

[0002] A robot is an automated mechanical device that imitates the functions of a human arm. With the increasing requirements for precision in mechanized processing, traditional robots can no longer meet production needs. Robots are beginning to develop in the direction of imitating human hands for use in more sophisticated application scenarios.

[0003] Existing humanoid hand robots are mostly assembled from knuckles and joints. Each component needs to be manufactured and assembled separately, which is a relatively complex process with a long production cycle and high cost. Some are directly manufactured using non-rigid connection structures, but they are highly dependent on machining and manufacturing precision and have very high height difference requirements. If the gap between the mating surfaces is too small, it will be unfavorable for manufacturing and post-processing. If the gap is too large, the joints will be too flexible and cause unstable movement. How to process it will increase cost and time. Summary of the Invention

[0004] The purpose of the present invention is to provide a mechanical finger structure based on additive manufacturing, which has an integrated flexible joint structure, simple processing technology, short processing cycle, and low cost. It is particularly suitable for occasions with small relative rotation, few working cycles and certain resilience.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solutions: a mechanical finger structure based on additive manufacturing, comprising a proximal phalanx and a distal phalanx, wherein the proximal phalanx and the distal phalanx are both formed of a skeleton by filling a variable-density diamond lattice, a metacarpophalangeal joint is integrally formed at the connection between the proximal phalanx and the palm, and the metacarpophalangeal joint is used to connect to the palm, and a flexible interphalangeal joint is integrally formed at the connection between the proximal phalanx and the distal phalanx, wherein the flexible interphalangeal joint comprises a plurality of integrally formed parallel thin-walled joint layers, wherein the plurality of thin-walled joint layers are coaxially arranged through a core shaft fixed therebetween, and an Archimedean spiral slot is left on the thin-walled joint layer with the core shaft as the center, so that the thin-walled joint layer forms an Archimedean spiral blade with an outer wall, and the adjacent Archimedean spiral blades have opposite rotation directions.

[0006] Preferably, the flexible interphalangeal joint has three thin-walled joint layers, including a first thin-walled joint layer, a second thin-walled joint layer, and a third thin-walled joint layer. The second thin-walled joint layer is integrally formed in the middle of the distal end of the proximal phalanx, and the first and third thin-walled joint layers are integrally formed with the proximal end of the distal phalanx. A limiting groove is provided between the two thin-walled joint layers of the distal phalanx, and the limiting groove cooperates with the corresponding arc change segment provided on the outer circumference of the second thin-walled joint layer to realize the transition from clearance fit to interference fit. When the rotation threshold is reached, the contact surface becomes an interference fit and stops rotating. The maximum forward rotation angle of the flexible interphalangeal joint is 60°, and the maximum reverse rotation angle is 30° or 40°.

[0007] Preferably, the metacarpophalangeal joint corresponding to the index finger is a spherical joint with a joint angle limit, and the metacarpophalangeal joint corresponding to the thumb is an ellipsoidal joint. The spherical joint and the ellipsoidal joint include an integrally formed joint groove and joint head.

[0008] Preferably, the joint groove of the ellipsoidal joint is a swept body groove type formed by horizontal rotation of the ellipsoid with the short axis as the rotation axis, and an ellipsoidal joint head matching the swept body groove type is integrally formed in the swept body groove type, which is used for rotation and positioning in the long axis plane of the metacarpophalangeal joint. An opening is provided at the upper end of the swept body groove type, and the opening is used for the extension of the ellipsoidal joint head shaft rod. A protrusion is provided on one side of the opening, and an arc-shaped surface is provided on the protrusion. The arc-shaped surface and the inner wall of the opening cooperate with the shaft rod for rotation and positioning in the short axis plane of the metacarpophalangeal joint.

[0009] Preferably, the material constituting the proximal knuckles, distal knuckles, metacarpophalangeal joints, and flexible interphalangeal joints of the mechanical finger is nylon.

[0010] Preferably, the Archimedean spiral blade formed by the thin-walled joint layer has N arms, 1≤N≤5.

[0011] The performance customization method of the flexible interphalangeal joint, a) The geometric parameters of the Archimedean spiral blade are as follows: Where Ra is the core radius, R is the joint radius, C is the pitch, and α is the helix angle; b) Establish a Cartesian coordinate system, and any point P in the configuration before deformation is expressed as , and the adjacent point Q is expressed as , after deformation, the coordinates of the two are expressed as, The change in the distance between points P and Q can be used to measure the magnitude of the deformation, and the Green strain tensor expressed in the coordinates before structural deformation can be obtained: , in, and is the deformation gradient tensor. is the Kronecker symbol; introduce the displacement field , the Green strain tensor expressed in displacement u is: ; c) From the time before the structure is deformed to the time after the structure is deformed, take any element on the structure to analyze the stress tensor, that is: , where is the Kirchhoff stress tensor corresponding to the Green strain tensor regarding the pre-deformation configuration, is the infinitesimal area before deformation Direction cosines of the upper normal, stress components on the area element before and after deformation and ; d) The structure is in the reference state before deformation, where stress and strain are both 0 and time The virtual displacement principle equivalent to the equilibrium condition of the structure in the time configuration is expressed as: , in, It's time The virtual work of the external load of the configuration, It's time The Euler stress tensor of the configuration, is the variation of the corresponding infinitesimal strain; By changing the reference of all variables to the initial equilibrium configuration and converting the Euler stress into the Kirchhoff stress tensor with respect to the initial configuration, we can obtain the virtual displacement principle of the TL format: , in Calculated as follows: , 、 are the volume and surface area of ​​the structure in its initial configuration, Represents the time from time t to Displacement increment component The variation of 、 are the equivalent load per unit initial surface area and the equivalent load per unit initial mass, respectively, and it is assumed that the area load and the volume force per unit mass applied to the object remain unchanged in different configurations; Introducing the concept of incremental decomposition, we can get the displacement increment The nonlinear solution equation of : , in, and From time t to The increments of Kirchhoff stress and Green strain of the configuration, and They are After decomposition, the displacement increment The linear and quadratic terms of , specifically expressed as, , , e) For the equation , perform linearization processing to obtain the nonlinear response results of the maximum stress node and the maximum displacement node, and determine the stages of the rotation process and the optimal number of arms; f) Using the orthogonal test method, the correlation between the joint core diameter, pitch, joint thickness, and screw angle parameters was tested to determine the order of influence of each factor on the rotation angle and lateral stability, thereby obtaining the joint parameter selection process; g) Establish a regression prediction model through response surface analysis to achieve performance requirement customization.

[0012] The additive manufacturing-based mechanical finger structure according to claim 1 is characterized in that the proximal finger joints and the distal finger joints are directly filled with variable density diamond lattices to form a skeleton method. 1) Base structure topology optimization: Using the variable density method, the base material of the design domain is set as a continuum with a variable density in the range [0,1]. Density is used as the design variable. The optimization goal is to minimize the flexibility of the structure under volume constraints, and obtain the node coordinates Ai, the number of elements n, and the relative density ρi of the grid; 2) Optimize the parametric layout of the unit cell. Perform a coarse finite element mesh on the design domain, preliminarily generate the unit cell and define the centroid coordinate Bj. The number of unit cells is N. The relative density mapping method is used. The material density information obtained from the continuum structure topology optimization results is used to calculate the relative density of the unit cells one by one. Starting from the first unit cell j=1, the distance rij between Ai and Bj is calculated, and the relative density value of the unit cell is calculated. The calculation formula is: The lattice unit structural parameters are determined by mapping the relative density ρj of the diamond lattice unit cell to the cross-sectional radius rj of the lattice unit rod. 3) Repeat the previous step until all unit cells are generated. Calculate whether the total volume of the lattice structure in the design domain meets the volume constraint, and then scale it to generate the final model.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. The mechanical finger structure of this application is based on additive manufacturing technology, with integrated molding and no assembly required, light weight, high specific strength, high durability and low cost; 2. The integrated flexible joint design has the ability to rotate and rebound. That is, when a force is applied, the joint rotates, and when the force is removed and the knuckle returns to its initial relaxed state. The rebound ability can provide better cushioning and adaptive grasping ability, enhancing the naturalness and flexibility of movement. 3. Through variable density diamond lattice filling, the diamond lattice structure provides excellent force transmission performance. At the same time, its adjustable density characteristics realize the lightweight of the knuckle structure, reduce the weight of mechanical components, and improve energy efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a structural schematic diagram of the present invention.

[0015] Figure 2 It is a top view of the present invention.

[0016] Figure 3 For the present invention Figure 2 Enlarged schematic diagram of the structure at point A.

[0017] Figure 4 It is a schematic diagram of the metacarpophalangeal joint structure of the present invention.

[0018] Figure 5 This is a schematic diagram of the thin-wall joint layer structure of the present invention.

[0019] Figure 6 This is the modeling diagram for the force deformation analysis of the flexible interphalangeal joint of the present invention.

[0020] Figure 7 This is the nonlinear finite element solution result of the embodiment of the present invention.

[0021] Figure 8 This is a schematic diagram of the design flow chart of the variable density diamond lattice structure of the present invention.

[0022] Figure 9 This is the parameter correlation effect curve.

[0023] In the figure: 1, proximal phalanx; 2, distal phalanx; 3, metacarpophalangeal joint; 4, interphalangeal joint; 401, second thin-walled joint layer; 402, first thin-walled joint layer; 403, third thin-walled joint layer; 404, limiting groove. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] See also Figure 1-7 , an embodiment provided by the present invention: A mechanical finger structure based on additive manufacturing includes a proximal phalanx 1 and a distal phalanx 2, a metacarpophalangeal joint 3, and a flexible interphalangeal joint 4 made of nylon. The nylon material has excellent wear resistance and impact resistance and is suitable for long-term use. Nylon is relatively light, which helps to reduce the weight of the entire finger joint system, making the device easier to operate and use. Nylon has good chemical corrosion resistance and wider applicability. The proximal phalanx 1 and the distal phalanx 2 are both filled with variable density diamond lattices 5 to form a skeleton. The skeleton filled with variable density diamond lattices 5 can effectively reduce weight and increase strength, and at the same time has high wear resistance, which can increase the durability and stability of the system and enable more flexible adjustment and higher adaptability.

[0026] The proximal phalanx 1 and the distal phalanx 2 are directly filled with variable density diamond lattice to form a skeleton method. 1) Base structure topology optimization: Using the variable density method, the base material of the design domain is set as a continuum with a variable density in the range [0,1]. Density is used as the design variable. The optimization goal is to minimize the flexibility of the structure under volume constraints, and obtain the node coordinates Ai, the number of elements n, and the relative density ρi of the grid; 2) Optimize the parametric layout of the unit cell. Perform a coarse finite element mesh on the design domain, preliminarily generate the unit cell and define the centroid coordinate Bj. The number of unit cells is N. The relative density mapping method is used. The material density information obtained from the continuum structure topology optimization results is used to calculate the relative density of the unit cells one by one. Starting from the first unit cell j=1, the distance rij between Ai and Bj is calculated, and the relative density value of the unit cell is calculated. The calculation formula is: The lattice unit structural parameters are determined by the mapping relationship between the relative density ρj of the diamond lattice unit cell and the cross-sectional radius rj of the lattice unit rod.

[0027] 3) Repeat the previous step until all unit cells are generated, calculate whether the total volume of the lattice structure in the design domain meets the volume constraint, and scale it appropriately to generate the final model.

[0028] The metacarpophalangeal joint 3 is integrally formed at the connection between the proximal phalanx 1 and the palm. The metacarpophalangeal joint 3 is used to connect with the palm. The metacarpophalangeal joint 3 is the connecting part between the proximal phalanx 1 and the palm, and plays the role of fixing the joint between the finger and the palm. The metacarpophalangeal joint 3 corresponding to the thumb adopts an ellipsoidal joint. The groove shape of the ellipsoidal joint matches the rotation threshold of each degree of freedom direction of the joint, which can effectively reduce the addition of support and improve post-processing problems; the metacarpophalangeal joint 3 corresponding to the index finger is a spherical joint.

[0029] A flexible interphalangeal joint 4 is integrally formed at the connection between the proximal phalanx and the distal phalanx 2. The flexible interphalangeal joint 4 includes three integrally formed parallel thin-walled joint layers. The three thin-walled joint layers are coaxially arranged through a core shaft. Each thin-walled joint layer is connected by an integrally formed core shaft fixed therebetween. Three Archimedean spiral grooves are concentrically and evenly distributed on the thin-walled joint layer with the core shaft as the center of the circle, so that the thin-walled joint layer forms a three-arm Archimedean spiral blade with an outer wall. The rotation stability can be improved by increasing the number of arms of the Archimedean spiral blade. The flexible fingertip joint relies on the bending elastic deformation generated by the thin-walled material under the action of torque to achieve the purpose of plane rotation of the connector. The adjacent Archimedean spiral blades rotate in opposite directions. The overall rotation angle of the two-way superimposed flexible fingertip joint is twice that of the unidirectional spiral flexible fingertip joint. The second thin-walled joint layer 401 of the flexible interphalangeal joint 4 is integrally formed in the middle of the distal end of the proximal phalanx 1, and the first and third thin-walled joint layers are integrally formed with the proximal end of the distal phalanx 2, and are arranged in parallel on both sides of the second thin-walled joint layer 401. Through the parallel stacking of the first thin-walled joint layer 402, the second thin-walled joint layer 401, and the third thin-walled joint layer 403, a limiting groove 404 is provided between the two thin-walled joint layers of the distal phalanx 2. The limiting groove 404 cooperates with the corresponding radian change segment arranged on the outer circumference of the second thin-walled joint layer 401. The radian change on the outer circumference can be flexibly designed according to needs. The design methods are all existing technologies. The limiting groove 404 is designed to limit the range of motion of the interphalangeal joint 4, and adopts a gradual transition from clearance fit to interference fit. As the joint rotates, when the rotation angle reaches the threshold, the contact surface pressure suddenly increases, and the static friction force is used to force it to stop. This design can avoid direct interference of the interference fit, such as sticking, and at the same time ensure that the joint can stably stop rotating after reaching the set rotation angle, and the joint does not Sudden changes in contact force will occur, thereby avoiding mechanical shock or unsmooth joint operation. In this embodiment, the maximum forward rotation angle of the flexible interphalangeal joint 4 is 60°, and the maximum reverse rotation angle is 30° or 40°. Through the design of the forward and reverse rotation angles, the joint can bend and stretch within a certain angle range, simulating real finger movements. Forward rotation provides finger bending movements, and reverse rotation provides finger stretching movements. The maximum reverse rotation angle of the index finger joint is 30°, and the maximum reverse rotation angle of the thumb joint is 40°. By limiting the rotation range of the joint, excessive bending or stretching is avoided, thereby improving accuracy and safety and avoiding mechanical damage.

[0030] The proximal phalanx 1, distal phalanx 2, metacarpophalangeal joint 3, and flexible interphalangeal joint 4 of the robotic finger of the present application are integrally formed by an additive manufacturing method. The integrated design avoids the connection parts in the traditional assembly design, reduces the looseness or instability problems that may occur between components, and greatly reduces the cost, improves the environmental adaptability and durability of the product; enhances the bionic movement ability of the robot arm and optimizes the driving efficiency; and the manufacturing materials have better adaptability, which can achieve lightweight structure and rigid-flexible material transition of the same joint.

[0031] The motion ability of the flexible interphalangeal joint 4 is closely related to the material properties. The relationship between its rotation ability and various structural parameters is also the key to further realize the functional customization design of the joint structure. For the performance customization method of the flexible interphalangeal joint 4, please refer to Figure 5-6 , a) The geometric parameters of the Archimedean spiral blade are as follows, (1) Where Ra is the core radius, R is the joint radius, C is the pitch, and α is the helix angle; b) During the rotation of the flexible interphalangeal joint, the structural motion and all external forces it bears can be represented in the same plane. At the same time, the external torque and constraint on the blade of the structure are uniform in its thickness direction. Therefore, the mid-surface of the structure in the thickness direction is selected as a schematic diagram to establish the model. The thickness direction is the X3 direction, which is perpendicular to the X1X2 plane. The core diameter is considered to be consolidated. The blade is subjected to the external torque T, resulting in small strain and large displacement deformation. like Figure 6 As shown, the solid box represents the local initial configuration, and the dotted box represents the local configuration in equilibrium at time t after the force is applied. The object under study in the Cartesian coordinate system continuously changes its configuration under the action of torque, that is, any point P in the configuration before structural deformation (at time 0) is expressed as 0 X i ( i =1,2,3), and the adjacent point Q is expressed as 0 X i +d 0 X i , after deformation (time t), the coordinates of the two are expressed as t X i = t X i ( 0 X 1 , 0 X 2 ,0 X 3 ), t X i +d t X i .

[0032] According to the theory of geometric nonlinearity, the change in the distance between the two points P and Q can be used to measure the magnitude of the deformation, and the strain tensor expressed in the coordinates before the structural deformation can be obtained - Green's strain tensor: (2), where and is the deformation gradient tensor. is the Kronecker symbol. Introducing the displacement field , the Green strain tensor expressed in terms of displacement u can be expressed as: (3) C) From time 0 to time t, take a certain surface element on the structure to analyze the stress tensor. Kirchhoff stipulates the stress components on the area element before and after deformation and Use and transform The same rules are connected. That is: (4) Where, It is the stress tensor corresponding to the Green strain tensor about the pre-deformation configuration - Kirchhoff stress tensor. is the infinitesimal area before deformation Direction cosines of the upper normal, The reference state is the initial state (time 0), where stress and strain are both 0. The virtual displacement principle is established using the incremental analysis method, with 0, t, Indicates the coordinates, displacement and other parameters of the structure at different times. The virtual displacement principle that is equivalent to the equilibrium condition of the structure in the time configuration can be expressed as: (5) in, It's time The virtual work of the external load of the configuration, It's time The Euler stress tensor of the configuration, is the variation of the corresponding infinitesimal strain, the reference of all variables is changed to the initial equilibrium configuration, and the Euler stress is converted into the Kirchhoff stress tensor with respect to the initial configuration, and the virtual displacement principle of the TL format is obtained: (6) in Calculated as follows: (7) 、 are the volume and surface area of ​​the structure in its initial configuration, Represents the time from time t to Displacement increment component The variation of 、 are the equivalent load per unit initial surface area and the equivalent load per unit initial mass, respectively, and it is assumed that the area load and the volume force per unit mass applied to the object remain unchanged in different configurations.

[0033] Introducing the concept of incremental decomposition, we can get the displacement increment The nonlinear solution equation of : (8) in, and From time t to The increments of Kirchhoff stress and Green strain of the configuration, and They are After decomposition, the displacement increment The linear term and quadratic term of . The specific expressions are: (9) (10) Formula (8) is processed linearly. Since the principle of normal operation of the joint structure is to keep the deformation of the material in the elastic reversible stage, it is assumed that the stress increment and strain increment Therefore, the tangent constitutive tensor with reference to the 0-position is introduced. To express this linear relationship, that is: (11) At the same time, when the incremental step size Small enough to allow right Approximation is performed. At this time, the linearized equation (8) is expressed as: (12) And ensure that the material is in the elastic stage, in the above incremental form of solving the equation, is a constant elastic constitutive tensor, which can be expressed as: (13) Where G and v are the elastic constants of the material. The solution domain is divided into finite elements. The coordinates and displacements of any point in the element after division are obtained by interpolating the coordinates and displacements of the element nodes: (14) (15) in, is the interpolation function of the node k, n represents the number of nodes, and Represent the coordinates and displacement components of node k in the i direction respectively. The upper left subscript can still be added with 0, t, etc. to represent the configuration at different times; The formal solution equation established on a unit is: (16) The four items in the above formula correspond to the four items in formula (12), u is the node displacement vector, is the vector obtained according to formula (7), 、 and It is expressed as follows: (17) (18) (19) Among the above 、 They are Green strain increment linear terms and nonlinear terms and the transformation matrix of the displacement, is the material constitutive matrix, and is the Kirchhoff stress matrix and vector.

[0034] The flexible interphalangeal joints of this embodiment were analyzed using the above method. The analysis results lead to the following conclusions: ①First, Figure 7 (b) The cross-sectional view shows that the stress distribution on the same longitudinal line of the joint is basically consistent. The stress distribution cloud diagram of the structure shows that there is a neutral surface within the thickness of the blade. The two ends of the neutral surface have stress distributions with opposite directions but basically the same values. During the simulation process, the maximum stress always occurs on the outside of the edge of the end where the blade connects to the core shaft.

[0035] ② From the displacement cloud map and the resulting configuration, the maximum displacement occurs at the outermost edge of the joint and is evenly distributed, and the displacement of the center point is 0. It can be seen that the three-arm spiral joint is more stable than the single-arm spiral joint, and there is basically no lateral floating, which is consistent with the function of joint rotation.

[0036] ③ Research on the rotation process of the joint found that when the blades of the joint are subjected to large force and deformation, they will inevitably come into contact with the adjacent arms at a certain moment, and under the continuous change of position, the three rotating arms squeeze each other, and the contact area continues to expand until the core diameter is covered layer by layer. During this period, the stress of the joint also gradually increases, gradually exceeding the elastic range of the material and even causing damage.

[0037] Taking the configuration of the joint when it contacts itself and the configuration when the maximum stress reaches the yield stress as the dividing points, the rotation of the joint is divided into three stages. In the first stage, the structure is only affected by the torque to produce a large configuration change. In the second stage, the structure is subjected to limited displacement by the torque and its own contact force, and the maximum stress of the structure reaches the yield stress during the deformation process. In the third stage, the external load continues to increase, and the material enters the inelastic stage. At this time, the change in the macro configuration is very small, but the material strain continues to increase, resulting in irreversible deformation. In summary, the joint rotation ability is the angle that the arm rotates to complete the second stage, and the torque it withstands to reach the final configuration of the second stage is the maximum torque.

[0038] The correlation between joint rotation performance and design parameters was studied by using the orthogonal test method to test the correlation between the parameters of joint core diameter, pitch, joint thickness and spiral angle, and the order of influence of each influencing factor on rotation angle and lateral stability was obtained, and the parameter selection process of the joint was obtained; the results obtained after the test are as follows: (1) Under the same torque, the factors affecting the maximum rotation angle of the joint are ranked as follows: helix angle > pitch > core diameter > joint thickness, and the influence of the helix angle on the joint rotation angle is much greater than the other three factors; the effect curve shows that the effect curves of pitch, core diameter and joint thickness are relatively horizontal, indicating that in the process of customizing the rotation angle, these three factors are secondary factors and can be considered later, while the helix angle should be selected as the dominant factor in joint design, and the larger the helix angle, the greater the joint rotation ability.

[0039] (2) Under the same torque, the factors affecting the maximum stress of the structure are ranked as follows: spiral angle > joint thickness > core diameter > pitch; the effect curve shows that the four factors have a significant effect on the maximum stress value of the structure, and the larger the joint thickness and core diameter, the greater the ability of the structure to resist damage. The pitch effect curve has a low value at level 2, indicating that the load-bearing condition of the structure here is better than the other two levels, while the spiral angle has a high value at level 2, indicating that when the spiral angle is 240°, the rotation of the joint is accompanied by a sharp increase in structural stress, and this situation should be avoided.

[0040] (3) Under the action of the same lateral force, the factors affecting the maximum stress of the structure are ranked as follows: spiral angle > joint thickness > core diameter > pitch; from the effect curve, it can be seen that the pitch and core diameter have little effect on the maximum stress of the structure under the same lateral force and can be considered later. At the same time, the spiral angle shows a unidirectional increasing trend in the three-level distribution, while the effect curve of the joint thickness shows a unidirectional decreasing trend. It can be seen that a small spiral angle and a large joint thickness are more conducive to the joint bearing lateral pressure.

[0041] (4) Under the action of the same lateral force, the factors affecting the maximum displacement of the structure are ranked as follows: helix angle > core diameter > joint thickness > pitch. It can be seen from the effect curve that the effect curves of the three factors of joint thickness, core diameter and pitch are relatively horizontal, and their influence on the displacement of the structure under the action of lateral force is relatively small. Relatively speaking, the influence of the helix angle is greater, and the larger its value is, the greater the lateral deformation of the structure.

[0042] The main function of a joint is rotation. Therefore, when designing a spiral joint, the first consideration is the degree of satisfaction of the rotation capacity, and the second consideration is its stability. That is, the spiral angle is selected under the premise of satisfying the rotation angle and stress range, and on this basis, the secondary parameters that can make the stability higher are selected. At the same time, the overall size of the joint must be used as a constraint to determine the final design parameters.

[0043] To predict target function parameters, response surface analysis was used to establish regression prediction models for each analysis indicator and determine the optimal solution for each factor. In this experiment, the four parameters of joint thickness, core diameter, thread pitch, and helix angle were represented by symbols A, B, C, and D, respectively. The regression model was established by fitting the experimental data to derive coefficients for the four parameters' independent terms, interaction terms, and quadratic terms, and verifying their significance.

[0044] Specifically, Design Expert software was used to calculate the regression equation, obtain the fitted regression equations for each indicator, and draw the model. Finally, the performance of the flexible interphalangeal joint was customized based on the results.

Claims

1. A mechanical finger structure based on additive manufacturing, characterized in that: The invention comprises a proximal phalanx (1) and a distal phalanx (2), wherein the proximal phalanx (1) and the distal phalanx (2) are both filled with a variable density diamond lattice to form a skeleton, a metacarpophalangeal joint (3) is integrally formed at the connection between the proximal phalanx (1) and the palm, and the metacarpophalangeal joint (3) is used to connect with the palm, and a flexible interphalangeal joint (4) is integrally formed at the connection between the proximal phalanx (1) and the distal phalanx (2), wherein the flexible interphalangeal joint (4) comprises a plurality of integrally formed parallel thin-walled joint layers, wherein the plurality of thin-walled joint layers are coaxially arranged through a core shaft fixed therebetween, and an Archimedean spiral slot is reserved on the thin-walled joint layer with the core shaft as the center of the circle, so that the thin-walled joint layer forms an Archimedean spiral blade with an outer wall, and the adjacent Archimedean spiral blades have opposite rotation directions.

2. The mechanical finger structure based on additive manufacturing according to claim 1, characterized in that: The flexible interphalangeal joint (4) has three thin-walled joint layers, including a first thin-walled joint layer (402), a second thin-walled joint layer (401), and a third thin-walled joint layer (403). The second thin-walled joint layer (401) is integrally formed at the middle of the distal end of the proximal phalanx (1). The first and third thin-walled joint layers are integrally formed at the proximal end of the distal phalanx (2). A limiting groove (404) is provided between the two thin-walled joint layers of the distal phalanx (2). The limiting groove (404) cooperates with the corresponding arc change segment provided on the outer circumference of the second thin-walled joint layer (401) to achieve a transition from a clearance fit to an interference fit. When a rotation threshold is reached, the contact surface becomes an interference fit and stops rotating. The maximum forward rotation angle of the flexible interphalangeal joint (4) is 60°, and the maximum reverse rotation angle is 30° or 40°.

3. The additive manufacturing-based robotic finger structure according to claim 1, characterized in that: The metacarpophalangeal joint (3) corresponding to the index finger is a spherical joint with a joint angle limit, and the metacarpophalangeal joint (3) corresponding to the thumb is an ellipsoidal joint. The spherical joint and the ellipsoidal joint include an integrally formed joint groove and a joint head.

4. The additive manufacturing-based robotic finger structure according to claim 3, characterized in that: The joint groove of the ellipsoidal joint is a swept body groove type formed by horizontally rotating the ellipsoid with the short axis as the rotation axis. The swept body groove type is integrally formed with an ellipsoidal joint head that matches the swept body groove type and is used for rotation and positioning in the long axis plane of the metacarpophalangeal joint (3). The upper end of the swept body groove type is provided with an opening, and the opening is used for the ellipsoidal joint head shaft to extend. A protrusion is provided on one side of the opening, and an arc surface is provided on the protrusion. The arc surface and the inner wall of the opening cooperate with the shaft rod to rotate and position in the short axis plane of the metacarpophalangeal joint (3).

5. The additive manufacturing-based robotic finger structure according to claim 1, characterized in that: The proximal phalanx (1), distal phalanx (2), metacarpophalangeal joint (3), and flexible interphalangeal joint (4) of the mechanical finger are made of nylon.

6. The additive manufacturing-based robotic finger structure according to claim 1, characterized in that: The Archimedean spiral blade formed by the thin-walled joint layer has N arms, 1≤N≤5.

7. The additive manufacturing-based robotic finger structure according to claim 1, characterized in that: The performance customization method of the flexible interphalangeal joint, a), the geometric parameter relationship of the Archimedean spiral blade is as follows: Where Ra is the core radius, R is the joint radius, C is the pitch, and α is the helix angle; b) Establish a Cartesian coordinate system, and any point P in the configuration before deformation is expressed as , and the adjacent point Q is expressed as , after deformation, the coordinates of the two are expressed as, The change in the distance between points P and Q can be used to measure the magnitude of the deformation, and the Green strain tensor expressed in the coordinates before structural deformation can be obtained: ， in, and is the deformation gradient tensor. is the Kronecker symbol; introduce the displacement field , the Green strain tensor expressed in displacement u is: ； c) From the time before the structure is deformed to the time after the structure is deformed, take any element on the structure to analyze the stress tensor, that is: , where is the Kirchhoff stress tensor corresponding to the Green strain tensor regarding the pre-deformation configuration, is the infinitesimal area before deformation Direction cosines of the upper normal, stress components on the area element before and after deformation and ; d) The structure is in the reference state before deformation, where stress and strain are both 0 and time The virtual displacement principle equivalent to the equilibrium condition of the structure in the time configuration is expressed as: ， in, It's time The virtual work of the external load of the configuration, It's time The Euler stress tensor of the configuration, is the variation of the corresponding infinitesimal strain; By changing the reference of all variables to the initial equilibrium configuration and converting the Euler stress into the Kirchhoff stress tensor with respect to the initial configuration, we can obtain the virtual displacement principle of the TL format: ， in Calculated as follows: , 、 are the volume and surface area of ​​the structure in its initial configuration, Represents the time from time t to Displacement increment component The variation of 、 are the equivalent load per unit initial surface area and the equivalent load per unit initial mass, respectively, and it is assumed that the area load and the volume force per unit mass applied to the object remain unchanged in different configurations; Introducing the concept of incremental decomposition, we can get the displacement increment The nonlinear solution equation of : ， in, and From time t to The increments of Kirchhoff stress and Green strain of the configuration, and They are After decomposition, the displacement increment The linear and quadratic terms of , specifically expressed as, ， , e) For the equation , perform linearization processing to obtain the nonlinear response results of the maximum stress node and the maximum displacement node, and determine the stages of the rotation process and the optimal number of arms; f) Using the orthogonal test method, the correlation between the joint core diameter, pitch, joint thickness, and screw angle parameters was tested to determine the order of influence of each factor on the rotation angle and lateral stability, thereby obtaining the joint parameter selection process; g) Establish a regression prediction model through response surface analysis to achieve performance requirement customization.

8. The additive manufacturing-based robotic finger structure according to claim 1, characterized in that: The proximal knuckle and distal direct variable density diamond lattice filling form the skeleton method, 1) Base structure topology optimization: Using the variable density method, the base material of the design domain is set as a continuum with a variable density in the range [0,1]. Density is used as the design variable. The optimization goal is to minimize the flexibility of the structure under volume constraints, and obtain the node coordinates Ai, the number of elements n, and the relative density ρi of the grid; 2) Optimize the parametric layout of the unit cell. Perform a coarse finite element mesh on the design domain, preliminarily generate the unit cell and define the centroid coordinate Bj. The number of unit cells is N. The relative density mapping method is used. The material density information obtained from the continuum structure topology optimization results is used to calculate the relative density of the unit cells one by one. Starting from the first unit cell j=1, the distance rij between Ai and Bj is calculated, and the relative density value of the unit cell is calculated. The calculation formula is: The lattice unit structural parameters are determined by mapping the relative density ρj of the diamond lattice unit cell to the cross-sectional radius rj of the lattice unit rod. 3) Repeat the previous step until all unit cells are generated. Calculate whether the total volume of the lattice structure in the design domain meets the volume constraint, and then scale it to generate the final model.

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