Stretchable pallet fork safety assessment method combined with finite element analysis

Abstract

The invention provides a telescopic pallet fork safety assessment method combined with finite element analysis. The method comprises the steps of load determination, wherein the load borne by a telescopic pallet fork in the working process is determined; a model selection and establishment step: establishing a finite element analysis model; material setting, wherein material parameters conforming to the actual working condition are set for all components of the telescopic pallet fork; a boundary condition adding step: adding a boundary condition in the finite element analysis model; grid division: performing grid division on the finite element analysis model; a result analysis step: obtaining a displacement cloud picture, a stress cloud picture and a strain cloud picture of the telescopic pallet fork under a given load, and extracting data; and a security assessment step: performing security assessment. According to the method, the finite element model is constructed, dynamic load input and multi-physical field coupling analysis are combined, the displacement, stress and strain cloud atlas of the pallet fork under the given load can be generated, and a basis is provided for strength checking, fatigue life prediction and lightweight design of the pallet fork.

Description

Technical Field

[0001] This invention relates to the field of automated warehousing equipment technology, specifically to a method for safety assessment of telescopic forks combined with finite element analysis, applicable to the design, manufacturing, and safety verification of telescopic forks of stacker cranes in intelligent automated warehouses and automated logistics warehousing systems. Background Technology

[0002] Automatic telescopic forks are a core component of intelligent automated warehouses and automated logistics storage systems, enabling the automatic storage, retrieval, and transfer of goods via stacker cranes. Their structures are divided into single-extension (three-section fork body) and double-extension types, and in terms of form, they are divided into single-row (light-duty, for small, light-weight items) and double-row (heavy-duty, for large, heavy-duty items).

[0003] Traditional telescopic fork designs rely on empirical formulas or simplified models, making it difficult to accurately account for the stress distribution in complex structures (such as rack and pinion engagement and weld areas). This can lead to excessively high safety margins or insufficient local strength. For example, during high-speed extension and retraction of a single-extension fork, the meshing impact between the rack and pinion can easily trigger fatigue cracks, but existing methods cannot quantitatively assess such dynamic effects. Furthermore, non-standard customized forks require repeated trial production and verification, resulting in long lead times and high costs. Summary of the Invention

[0004] The main objective of this invention is to provide a safety assessment method for telescopic forks that combines finite element analysis. By constructing a high-precision finite element model and combining dynamic load input and multiphysics coupling analysis, the method accurately generates displacement, stress, and strain cloud maps of the fork under a given load and extracts the maximum value data, providing a basis for fork strength verification, fatigue life prediction, and lightweight design.

[0005] The present invention achieves the above objectives through the following technical solutions: A method for safety assessment of telescopic forks combined with finite element analysis includes: Load determination steps: Determine the loads that the telescopic forks will bear during operation, including at least permanent loads and live loads; Model selection and establishment steps: Based on the actual structure and working state of the telescopic fork, establish a finite element analysis model, wherein the finite element analysis model needs to comprehensively consider the shape and size of the telescopic fork, the support method and the material properties; Material setting steps: In the finite element analysis model, set material parameters for each component of the telescopic fork that conform to the actual working conditions; Steps for adding boundary conditions: Add boundary conditions to the finite element analysis model based on the actual working state of the telescopic forks; Mesh generation steps: The finite element analysis model is meshed using standard mesh settings; Results analysis steps: Run the finite element analysis model to obtain the displacement cloud map, stress cloud map and strain cloud map of the telescopic fork under a given load, and extract the maximum displacement, maximum stress and maximum strain data; Safety assessment steps: Compare the maximum stress obtained from the analysis with the yield strength of the material to ensure that the maximum stress is lower than the yield strength of the material and that the yield strength of the material exceeds the maximum stress by a predetermined multiple, so as to meet the safety strength design requirements.

[0006] According to the present invention, a safety assessment method for telescopic forks combined with finite element analysis is provided. When determining the permanent load, the self-weight of the telescopic fork and the weight of the fixed attachment components are obtained by measurement or theoretical calculation and used as the permanent load. The self-weight of the telescopic fork is calculated by multiplying the material density and volume, and the weight of the fixed attachment components is obtained by actual weighing or design parameters. When determining the live load, the live load is determined based on the maximum weight of the items stored, retrieved, or transferred in the actual application scenario of the telescopic forks; the maximum weight is obtained through customer-specified requirements, industry standards, or experimental tests, and a dynamic load factor is considered to cover the impact or vibration effects in actual working conditions. The permanent load and the live load are combined according to the most unfavorable working condition to form the calculation load, which is used as the input condition for the finite element analysis model.

[0007] According to the present invention, a safety assessment method for telescopic forks combined with finite element analysis is provided. During the finite element analysis process, the stress and strain distribution of the telescopic fork steel structure is calculated, including: The steel structure of the telescopic fork is discretized into a finite number of elements, each of which is regarded as an independent small structure. The elements are connected by nodes to form an overall finite element model. The element type is selected as beam element, shell element or solid element according to the structural characteristics. For the beam structure characteristics of telescopic forks, either Euler-Bernoulli beam theory or Timoshenko beam theory is selected to establish a calculation model. Euler-Bernoulli beam theory is suitable for small deformation and linear elastic material conditions, while Timoshenko beam theory is suitable for conditions that consider the influence of shear deformation. Based on the actual working conditions, combine permanent loads and live loads to calculate the structural response under uniformly distributed load q or concentrated load P. Calculate the maximum deflection of a simply supported beam under a uniformly distributed load; calculate the bending normal stress at a point on the cross section; calculate the bending shear stress at a point on the cross section of a rectangular beam. Eigenvalue buckling analysis is performed on the compression member to obtain the critical load value; Calculate the critical load Pcr of the ideal compression member to ensure that the actual working load is less than the predetermined safety factor multiple of the critical load; Compare the calculated maximum deflection value with the limit specified in the design code; If the maximum deflection exceeds the limit, adjust the structural parameters or recombine the loads until the safety requirements are met.

[0008] According to the present invention, a method for safety assessment of telescopic forks combined with finite element analysis is provided. The establishment of the finite element analysis model includes: Based on the actual structural parameters of the telescopic fork, including the number of sections of the single or double extension fork body, the arrangement of the fork arms, the shape and size of each component and their connection relationship, a geometric model is constructed using 3D modeling software or finite element preprocessing tools. Based on the working state of the telescopic forks, the fixed constraint positions and kinematic pair relationships are defined, and the actual support is simulated through the boundary condition module; Assign material parameters to each component of the geometric model. The main structure uses 42CrMo steel, and its elastic modulus E, yield strength, Poisson's ratio and other parameters are input from the material handbook or experimental data. Define the interaction relationships such as sliding contact between forks and meshing contact between gears and racks, and set the friction coefficient; at the same time, simulate the transmission connection of components such as couplings and reducers through coupling or rigid body constraints; Non-critical details are simplified to improve computational efficiency, and the rationality of the model is verified through static balance verification or modal analysis to ensure that it can accurately reflect the actual force and deformation characteristics of the telescopic fork.

[0009] According to the present invention, a safety assessment method for telescopic forks combined with finite element analysis is provided, which sets material parameters for each component of the telescopic fork that conform to actual working conditions, specifically including: Based on the actual working conditions of the telescopic forks, including load type, operating frequency and environmental factors, 42CrMo steel was selected as the main structural material. Obtain the key parameters of 42CrMo steel through material handbooks, experimental tests or data provided by suppliers, and input them into the property definition module of the finite element analysis model. These key parameters include at least the elastic modulus E, yield strength, tensile strength, Poisson's ratio and density. For different components of the telescopic fork, corresponding material parameters are set according to their actual functions and stress characteristics; For components subject to plastic deformation or large deformation, enable the nonlinear material model in the finite element software and input stress-strain curve data to accurately simulate the material behavior under ultimate load. By comparing theoretical calculations with experimental test results, the accuracy of material parameter settings is verified, ensuring that the finite element analysis results can truly reflect the mechanical properties of the telescopic fork.

[0010] According to the present invention, a method for safety assessment of telescopic forks combined with finite element analysis is provided, which adds boundary conditions to the finite element analysis model, including: Apply a fixed constraint to the bottom mounting surface of the assembly: Based on the installation method of the telescopic fork, a full-degree-of-freedom fixed constraint is applied to the bottom mounting surface of the finite element model to constrain all translational and rotational degrees of freedom in order to simulate the rigid connection between the telescopic fork and the base or equipment. Use a geometric coordinate system or node selection tool to accurately locate the mounting surface nodes and ensure that constraints are applied to the actual contact area. If there are multiple mounting points, local constraints should be applied to each mounting point separately to avoid stress concentration distortion caused by overall constraints. If elastic elements are present during actual installation, a spring-damping unit is inserted between the fixed constraint and the mounting surface, and the stiffness coefficient and damping coefficient are input to simulate the dynamic response characteristics of the flexible support.

[0011] According to the present invention, a method for safety assessment of telescopic forks combined with finite element analysis is provided, which adds boundary conditions to the finite element analysis model, including: Apply loads to the right end face or other designated locations according to the actual load conditions: Based on the actual working scenario of the telescopic forks, the following types of loads are applied: Concentrated force: A vertically downward concentrated force is applied to the center node or key load-bearing point on the right end face of the telescopic fork to simulate the weight of the cargo or impact load. Distributed force: If the load distribution is uneven, apply a pressure load to the right end face and define the load gradient through the pressure distribution function; Torque load: Applying bending moment or torque to the rotating shaft or connecting parts of the telescopic fork to simulate the inertial force or external driving torque when the telescopic fork extends or rotates; If the telescopic forks are subjected to alternating loads, the time history load input curve of the load changing over time can be used, or a multi-level load cycle can be defined through the fatigue load spectrum to support fatigue life analysis.

[0012] According to the present invention, a method for safety assessment of telescopic forks combined with finite element analysis is provided, which adds boundary conditions to the finite element analysis model and further includes: For the sliding joint of the telescopic fork, a sliding constraint is applied between the contact surfaces to restrict other degrees of freedom except for the direction of motion, and a friction coefficient is set to simulate actual transmission loss. For connections with gaps, set an initial gap or preload in the contact definition to reflect assembly errors or preload conditions; If the telescopic fork is dynamically coupled to other components, the finite element model can be connected to the dynamic model through rigid-flexible coupling or multibody dynamics interface, and dynamic parameters such as rotational speed or acceleration can be input.

[0013] According to the present invention, a method for safety assessment of telescopic forks combined with finite element analysis is provided, wherein obtaining the displacement contour map, stress contour map, and strain contour map of the telescopic fork under a given load includes: Displacement cloud map: Select the total displacement or displacement in a specified direction as the output variable; display the displacement distribution through cloud map coloring, set the color scale range and contour line interval to intuitively present the deformation trend of the telescopic fork; mark the displacement values ​​of key nodes and generate a 3D displacement vector map to show the deformation direction.

[0014] Stress cloud map: Select equivalent stress or principal stress as output variable, set color scale range and contour line interval; for welded joints or stress concentration areas, enable local mesh refinement display and overlay stress gradient arrows to indicate high stress direction; generate stress extreme point markers and automatically label the location and value of maximum stress; Strain contour plot: Select equivalent strain or principal strain as the output variable, set the color scale range and contour interval; for plastic deformation regions, enable strain hardening curve overlay to display the strain-stress relationship to assess material damage; generate strain path tracing to record the strain variation curves of key nodes with time or load step.

[0015] According to the present invention, a method for safety assessment of telescopic forks combined with finite element analysis is provided, which extracts maximum displacement, maximum stress, and maximum strain data, including: Maximum displacement extraction: Call the extreme value query function to automatically search for the maximum total displacement and coordinate position of all nodes in the model; output the maximum displacement value to a text file or Excel spreadsheet, and mark the corresponding load step and time point; generate displacement-time curves or displacement-load curves to analyze the variation law of displacement with external conditions. Maximum stress extraction: Locate the location of the maximum equivalent stress or maximum principal stress in the model using the stress extremum search function; extract the maximum stress value and its element number and material properties, and determine whether it exceeds the material yield strength σy; generate a stress concentration factor calculation report; Maximum strain extraction: The strain extremum analysis function is invoked to obtain the location of the maximum equivalent strain and the maximum principal strain; the strain value and its path are extracted, and it is determined whether the material fracture strain has been reached; strain-life curve data points are generated to provide input for fatigue analysis.

[0016] Therefore, compared with the prior art, the telescopic fork safety assessment method proposed in this invention, which combines finite element analysis, has the following beneficial effects: 1. This invention, through finite element analysis, can visually present the stress distribution cloud map of telescopic forks under different working conditions (such as static, longitudinal impact, acceleration, braking, turning, etc.), accurately locate high-stress areas (such as the turning point at the fork root, the welding position between the longitudinal and transverse plates, etc.), and identify potential fracture risk points in advance. This invention simulates the dynamic deformation behavior of telescopic forks when carrying goods, assesses their rigid deformation, vibration amplitude, and stability, and avoids goods slipping or equipment overturning due to excessive deformation. This invention, through localized mesh refinement and dynamic load input, can accurately quantify the maximum stress value, further reducing errors.

[0017] 2. Based on finite element analysis results, this invention selects high-strength alloy steel (such as Q345B, 45# steel) or performs quenching treatment to enhance the bending and fatigue resistance of the forks and increase the load-bearing capacity (e.g., heavy-duty models can bear over 5000 kg). For stress concentration areas, the cross-sectional shape of the forks is optimized (e.g., thickening the fork tooth root and using multi-segment slide rail synchronous transmission) to balance the stress distribution and avoid excessive local stress. While ensuring strength, the structural layout is optimized through finite element analysis to reduce redundant materials, lower the fork weight, and improve equipment flexibility and energy efficiency.

[0018] 3. The method of this invention is applicable to all types of forklift designs, including single-extension, double-extension, single-row, and double-row forks, and can be extended to the safety assessment of other automated warehousing equipment (such as conveyors and elevators). Through a modular modeling process, engineers only need to adjust input parameters (such as load and stroke) to complete the rapid development of new products.

[0019] 4. This invention simulates the fatigue damage process of telescopic forks under alternating stress, assesses their service life, guides maintenance cycle formulation, and reduces unexpected failures. For harsh environments such as ports and docks, finite element analysis is used to verify the effectiveness of anti-corrosion treatments (such as galvanizing and spraying anti-corrosion coatings), ensuring long-term stable operation of the equipment in salt spray and humid environments.

[0020] 5. This invention uses finite element simulation to replace traditional model testing, quickly verifying the feasibility of the design scheme, reducing the number of physical prototype fabrication and testing, and shortening the R&D cycle. It avoids structurally weak points during the design phase, preventing rework or material waste due to insufficient strength, and reducing R&D costs.

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0022] Figure 1 This is a flowchart of an embodiment of a telescopic fork safety assessment method combining finite element analysis according to the present invention.

[0023] Figure 2This is a schematic diagram of the structure of the telescopic fork in an embodiment of the safety assessment method for telescopic forks combined with finite element analysis of the present invention.

[0024] Figure 3 This is a schematic diagram of the model regarding the design input conditions in an embodiment of the safety assessment method for telescopic forks combined with finite element analysis according to the present invention.

[0025] Figure 4 This is a schematic diagram of the parameters of 42CrMo in an embodiment of a safety assessment method for telescopic forks combined with finite element analysis according to the present invention.

[0026] Figure 5 This is a schematic diagram of the structure with added boundary conditions in an embodiment of the safety assessment method for telescopic forks combined with finite element analysis of the present invention.

[0027] Figure 6 This is a schematic diagram of the mesh division structure in an embodiment of the safety assessment method for telescopic forks combined with finite element analysis of the present invention.

[0028] Figure 7 This is a schematic diagram of the displacement cloud map results in an embodiment of the safety assessment method for telescopic forks combined with finite element analysis according to the present invention.

[0029] Figure 8 This is a schematic diagram of the stress cloud diagram results in an embodiment of the safety assessment method for telescopic forks combined with finite element analysis according to the present invention.

[0030] Figure 9 This is a schematic diagram of the strain cloud diagram results in an embodiment of a safety assessment method for telescopic forks combined with finite element analysis according to the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0033] An Example of a Safety Assessment Method for Telescopic Forks Combining Finite Element Analysis See Figures 1 to 9 This embodiment provides a method for safety assessment of telescopic forks combined with finite element analysis, including: Load determination step S1: Determine the loads borne by the telescopic forks during operation, including at least permanent loads and live loads; Model selection and establishment step S2: Based on the actual structure and working state of the telescopic fork, establish a finite element analysis model, wherein the finite element analysis model needs to comprehensively consider the shape and size of the telescopic fork, the support method and the material properties; Material setting step S3: In the finite element analysis model, set material parameters for each component of the telescopic fork that conform to the actual working conditions; Step S4: Add boundary conditions to the finite element analysis model according to the actual working state of the telescopic forks. Meshing step S5: Mesh the finite element analysis model using standard mesh settings; Result analysis step S6: Run the finite element analysis model to obtain the displacement cloud map, stress cloud map and strain cloud map of the telescopic fork under a given load, and extract the maximum displacement, maximum stress and maximum strain data. Safety assessment step S7: Compare the maximum stress obtained from the analysis with the yield strength of the material to ensure that the maximum stress is lower than the yield strength of the material and that the yield strength of the material exceeds the predetermined multiple of the maximum stress, so as to meet the safety strength design requirements.

[0034] When determining the permanent load, the weight of the telescopic fork and the weight of the fixed attachment components are obtained by measurement or theoretical calculation and are used as the permanent load. The weight of the telescopic fork is calculated by multiplying the material density and volume, and the weight of the fixed attachment components is obtained by actual weighing or design parameters. When determining the live load, the live load is determined based on the maximum weight of the items stored, retrieved, or transferred in the actual application scenario of the telescopic forks; the maximum weight is obtained through customer-specified requirements, industry standards, or experimental tests, and a dynamic load factor is considered to cover the impact or vibration effects in actual working conditions. The permanent load and the live load are combined according to the most unfavorable working condition to form the calculation load, which is used as the input condition for the finite element analysis model.

[0035] In the finite element analysis process, the stress and strain distribution of the telescopic fork steel structure are calculated, including: The steel structure of the telescopic fork is discretized into a finite number of elements, each of which is regarded as an independent small structure. The elements are connected by nodes to form an overall finite element model. The element type is selected as beam element, shell element or solid element according to the structural characteristics. For the beam structure characteristics of telescopic forks, either Euler-Bernoulli beam theory or Timoshenko beam theory is selected to establish a calculation model. Euler-Bernoulli beam theory is suitable for small deformation and linear elastic material conditions, while Timoshenko beam theory is suitable for conditions that consider the influence of shear deformation. Based on the actual working conditions, combine permanent loads and live loads to calculate the structural response under uniformly distributed load q or concentrated load P. The formula δmax=5qL is used. 4 / 384EI calculates the maximum deflection of a simply supported beam under a uniformly distributed load, where L is the beam span, E is the material's elastic modulus, and I is the moment of inertia of the cross section. The bending normal stress at a point on the cross section is calculated using the formula σ=M·y / I, where M is the bending moment and y is the vertical distance from the neutral axis to the stress point. The bending shear stress at a point on the cross section of a rectangular section is calculated using the formula τ=V·Q / (I·b), where V is the shear force, Q is the static moment of area, and b is the width of the section. Eigenvalue buckling analysis is performed on the compression member to obtain the critical load value; Using the formula Pcr=π 2 EI / (KL) 2 Calculate the critical load (Pcr) of an ideal compression member, where K is the length coefficient and L is the effective length of the member; Ensure that the actual working load is less than the predetermined safety factor multiple of the critical load; Compare the calculated maximum deflection value with the limit specified in the design code (such as L / 250 or L / 400); If the maximum deflection exceeds the limit, adjust the structural parameters (such as cross-sectional dimensions and material grade) or recombine the loads until the safety requirements are met.

[0036] In this embodiment, the establishment of the finite element analysis model specifically includes: Based on the actual structural parameters of the telescopic fork, including the number of sections of the single or double extension fork body, the arrangement of the fork arms (single-row or double-row), the shape, size and connection relationship of each component, a geometric model is constructed using 3D modeling software or finite element preprocessing tools. Based on the working state of the telescopic forks, the fixed constraint positions (such as the mounting surface at the bottom of the assembly) and the kinematic pair relationships (such as sprocket and chain drive, gear and rack meshing) are defined, and the actual support is simulated through the boundary condition module; Assign material parameters to each component of the geometric model. The main structure uses 42CrMo steel, and its elastic modulus (E), yield strength, Poisson's ratio and other parameters are input from the material handbook or experimental data. Define the interaction relationships such as sliding contact between forks and meshing contact between gears and racks, and set the friction coefficient; at the same time, simulate the transmission connection of components such as couplings and reducers through coupling or rigid body constraints; Non-critical details (such as chamfers and small holes) are simplified to improve computational efficiency, and the rationality of the model is verified through static balance verification or modal analysis to ensure that it can accurately reflect the actual force and deformation characteristics of the telescopic fork.

[0037] Select mesh generation and cell type: Fork-arm structure: Shell elements are used to simulate thin-walled box-shaped sections, and the mesh size is controlled at 5~10mm to balance computational accuracy and efficiency; Gears and drive shafts: Solid elements are used to capture the contact stress and axial bending deformation of the gear surface, and the mesh of the contact area is refined (mesh size ≤ 2 mm). Welded joints: A transition mesh is used at the weld location, gradually refining from a coarse mesh (base material area) to a fine mesh (heat-affected zone) to accurately simulate the distribution of residual welding stress; Define contact and connection relationships: Gear and rack meshing: The interaction between the tooth surfaces is defined by surface-to-surface contact, and the friction coefficient (μ=0.1) and contact stiffness (KN=1000 N / mm) are set. Bolted connection: The bolt preload is simulated by coupling node degrees of freedom (DOF) or tie constraint. The preload value (e.g., F=50 kN) is input to reflect the connection strength. Sprocket and chain drive: Gap contact is used to simulate the meshing process between the chain and the sprocket, and an initial gap (δ=0.5 mm) is set to avoid numerical divergence.

[0038] The model was validated and revised. Static verification: Apply a unit load (e.g., 1 N·m bending moment) to the simplified model, calculate the stress values ​​of key parts, and compare them with the results of theoretical formulas (e.g., σ=M·y / I). The error should be ≤10%. Dynamic verification: Obtain the first three natural frequencies (f1, f2, f3) of the telescopic fork through modal analysis, and compare them with experimental test results (such as the hammer impact method). The frequency error should be ≤5%. If the verification results do not meet the accuracy requirements, adjust the mesh density, contact parameters, or material properties until the model calculation results closely match the actual working conditions.

[0039] In this embodiment, material parameters are set for each component of the telescopic fork to conform to actual working conditions, specifically including: Based on the actual working conditions of the telescopic forks, including load type, operating frequency and environmental factors, 42CrMo steel was selected as the main structural material. Obtain the key parameters of 42CrMo steel through material handbooks, experimental tests or data provided by suppliers, and input them into the property definition module of the finite element analysis model. These key parameters include at least the elastic modulus E, yield strength, tensile strength, Poisson's ratio and density. For different components of the telescopic fork (such as fork body, gear, rack, and connecting plate), corresponding material parameters are set according to their actual functions and stress characteristics. For components subject to plastic deformation or large deformation, enable the nonlinear material model in the finite element software and input stress-strain curve data to accurately simulate the material behavior under ultimate load. By comparing theoretical calculations with experimental test results (such as tensile tests and hardness tests), the accuracy of material parameter settings is verified, ensuring that the finite element analysis results can truly reflect the mechanical properties of the telescopic fork.

[0040] For high-speed operation or impact load conditions, the rate-dependent material model of the finite element software is enabled, and the dynamic elastic modulus (Edyn=1.1E) and dynamic yield strength (σydyn=1.2σy) are input. For low-temperature environments (below -20℃), adjust the fracture toughness parameters (KIC value reduced by 20%) based on the material's low-temperature brittleness test data.

[0041] If the telescopic forks involve thermo-mechanical coupling conditions (such as high-temperature braking friction), the coefficient of thermal expansion (α=12×10) should be added to the material parameters. -6 / ℃) and thermal conductivity (λ=42 W / (m·K)); For corrosive environments, the material corrosion rate (e.g., 0.1 mm / year) and the cross-sectional attenuation coefficient after corrosion are defined to assess long-term service safety.

[0042] In this embodiment, boundary conditions are added to the finite element analysis model, specifically including: Apply a fixed constraint to the bottom mounting surface of the assembly: Constraint type selection: Based on the installation method of the telescopic fork (such as flange connection, bolt fixing), apply a full-degree-of-freedom fixed constraint to the bottom mounting surface of the finite element model, constraining all translational degrees of freedom (UX=UY=UZ=0) and rotational degrees of freedom (ROTX=ROTY=ROTZ=0) to simulate the rigid connection between the telescopic fork and the base or equipment; Constraint location positioning: Use a geometric coordinate system or node selection tool to accurately locate the mounting surface nodes and ensure that the constraints are applied to the actual contact area; if there are multiple mounting points (such as 4 bolt holes), local constraints need to be applied to each mounting point separately to avoid stress concentration distortion caused by overall constraints; Elastic support supplement: If elastic elements (such as rubber damping pads or springs) exist in the actual installation, insert a spring-damping unit between the fixed constraint and the mounting surface, and input the stiffness coefficient (K, unit: N / mm) and damping coefficient (C, unit: N·s / mm) to simulate the dynamic response characteristics of the flexible support.

[0043] Apply loads to the right end face or other designated locations according to the actual load conditions: Load type definition: Based on the actual working scenario of the telescopic forks, the following types of loads are applied: Concentrated force: A vertically downward concentrated force (F, unit: N) is applied to the center node or key load-bearing point on the right end face of the telescopic fork to simulate the weight of the cargo or impact load. Distributed force: If the load distribution is uneven (e.g., uneven loading of goods), apply a compressive load (force per unit area, q, unit: N / mm²) to the right end face. 2 The load gradient is defined by a pressure distribution function (such as linear distribution or parabolic distribution). Torque load: Applying a bending moment (M, unit: N·m) or torque (T, unit: N·m) to the rotating shaft or connection of the telescopic fork to simulate the inertial force or external driving torque during the extension or rotation of the fork; Load direction calibration: Use coordinate system transformation tools to ensure that the load direction is consistent with the actual working conditions (e.g., the gravity direction is -Z axis, and the torque direction rotates around the X axis). Dynamic load supplement: If the forks are subjected to alternating loads (such as frequent extension and contraction, vibration), the time history load is used to input the curve of load change over time (such as sine wave, step signal), or multi-level load cycles are defined through fatigue load spectrum to support fatigue life analysis.

[0044] For sliding joints of forks (such as rack and pinion guides, sprockets and chains), a sliding constraint (Translational Joint) is applied between the contact surfaces to restrict other degrees of freedom except for the direction of motion, and a friction coefficient (μ=0.1~0.3) is set to simulate actual transmission losses; For connections with gaps (such as gear meshing and bolted connections), set the initial gap (δ, unit: mm) or preload (Fpre, unit: kN) in the contact definition to reflect assembly errors or preload conditions; If the forks are dynamically coupled to other components (such as drive motors and drive shafts), the finite element model can be connected to the dynamic model through rigid-flexible coupling or multibody dynamics interface, and dynamic parameters such as rotational speed or acceleration can be input.

[0045] In this embodiment, obtaining the displacement contour map, stress contour map, and strain contour map of the telescopic fork under a given load includes: Displacement cloud plot: Select the total displacement or displacement in a specified direction (such as UX, UY, UZ) as the output variable; display the displacement distribution through cloud plot color map, set the color scale range (such as 0~10 mm) and contour line interval (such as 1 mm / level) to intuitively present the fork deformation trend; mark the displacement values ​​of key nodes (such as the displacement of the center node of the right end face) and generate a three-dimensional displacement vector plot to show the deformation direction.

[0046] Stress cloud map: Select equivalent stress (Von Mises Stress) or principal stresses (S1, S2, S3) as output variables, set the color scale range (e.g., 0~500 MPa) and contour line interval (e.g., 50 MPa / level); for welded joints or stress concentration areas, enable local mesh refinement and overlay stress gradient arrows to indicate high stress directions; generate peak stress markers to automatically mark the location and value of the maximum stress; Strain contour plot: Select equivalent plastic strain or principal strains (E1, E2, E3) as output variables, set the color scale range (e.g., 0~0.05) and contour line interval (e.g., 0.005 / level); for plastic deformation regions, enable strain hardening curve overlay to display the strain-stress relationship to assess material damage; generate strain path tracking to record the strain variation curves of key nodes over time or load steps.

[0047] In this embodiment, the extraction of maximum displacement, maximum stress, and maximum strain data includes: Maximum Displacement Extraction: The Extreme Value Query function is invoked to automatically search for the maximum total displacement (Umax) and its coordinates (X, Y, Z) of all nodes in the model; the maximum displacement value is output to a text file (.txt) or Excel spreadsheet, and the corresponding load step (e.g., Step 2, Substep 5) and time point (e.g., t=0.2 s) are labeled; a displacement-time curve or a displacement-load curve is generated to analyze the variation of displacement with external conditions; Maximum stress extraction: The Stress Peak Search function locates the position of the maximum equivalent stress (σmax, Von Mises) or the maximum principal stress (σ1, max) in the model; extracts the maximum stress value and its element ID, material properties (e.g., 42CrMo steel), and determines whether it exceeds the material yield strength (σy); generates a stress concentration factor (Kt=σmax / σnominal) calculation report, where σnominal is the nominal stress; Maximum strain extraction: Call the strain peak analysis function to obtain the location of the maximum equivalent strain (εmax) and the maximum principal strain (ε1,max); extract the strain value and its path (such as the heat-affected zone of the weld, tooth root fillet), and determine whether the material fracture strain εf has been reached; generate strain-life curve (ε-N Curve) data points to provide input for fatigue analysis.

[0048] The deflection calculation of the telescopic fork steel structure provided in this embodiment needs to consider many factors, such as shape and size, support method, and material properties. Generally, the finite element method (FEM) is used for calculation. The FEM is a numerical calculation method applicable to static and dynamic analysis of various complex structures and is one of the main methods for safety calculation of telescopic forks.

[0049] In the finite element method, the steel structure of the telescopic fork is divided into many small elements, each of which can be considered a miniature structure. By calculating these small elements, the stress and strain distribution of the entire telescopic fork steel structure can be obtained. During the calculation process, the influence of various factors needs to be considered, such as load magnitude and speed. The stress and strain data of the telescopic fork steel structure obtained from the calculation can provide a strong safety reference for the design and manufacture of telescopic forks.

[0050] like Figure 2As shown, the transmission principle of the entire telescopic fork is as follows: the motor transmits power to the sprocket at the end of the reducer shaft through a coupling and a reducer. The sprocket at the reducer shaft then transmits power to the drive shaft through a chain. The sprocket on the drive shaft and the sprocket at the end of the reducer shaft are the same size, and the sprocket-chain transmission ratio is one. The gear installed at the end of the drive shaft transmits power to the middle fork through the middle fork rack plate, causing the middle fork to move relative to the lower fork at a certain speed. The double-meshing gear installed on the middle fork connecting plate moves together with the middle fork at the same speed. The lower part of the double-meshing gear meshes with the rack on the lower fork rack plate, and the upper part meshes with the rack on the upper fork rack plate. The lower fork rack plate remains stationary, while the upper fork rack plate moves forward at twice the speed of the middle fork.

[0051] When the motor reverses, the middle and upper forks move in opposite directions, enabling bidirectional loading and unloading of goods. A bidirectional baffle welded to the lower fork base plate works in conjunction with a bidirectional baffle welded to the bottom of the middle fork connecting plate. When the forks reach their limit positions, the upper and lower bidirectional baffles collide, stopping the forks. The coupling is a torque-limiting coupling; when the torque exceeds a set value, the steel balls inside the coupling slip, protecting the forks from damage and improving system safety.

[0052] After determining the loads, including permanent loads and live loads, these loads will serve as the basis for calculating deflection. The next step is to select a calculation model: choose an appropriate beam theory for analysis; apply mechanical formulas: calculate the deflection under different load combinations, such as the Euler-Bernoulli beam theory formulas. For compression members, ensure that instability does not occur under critical loads. Finally, verify the deflection limits: the calculated deflection values ​​need to be compared with the limits specified in the design code to ensure the safety and functionality of the structure.

[0053] The above calculations involve factors such as the material's elastic modulus (E), moment of inertia (I), load (P or q), and span (L). For example, for a simply supported beam under a uniformly distributed load, its maximum deflection can be expressed as: δmax = 5qL^4 / 384EI, where δmax is the maximum deflection, q is the uniformly distributed load per unit length, L is the beam's span, E is the material's elastic modulus, and I is the moment of inertia.

[0054] The internal stresses are mainly bending normal stress and bending shear stress. The bending internal stress is usually calculated using the following formula: 1. Bending normal stress is caused by the bending moment and is perpendicular to the cross-section. It is linearly distributed along the height of the beam. The calculation formula is: σ = M * y / I, where σ is the bending normal stress at a point on the cross-section (unit: Pa, N / m). 2M is the bending moment (unit: N·m) on the cross section, and y is the perpendicular distance (unit: m) from the neutral axis of the cross section to the stress point. 2. Bending Shear Stress: Bending shear stress is caused by shear force and is parallel to the cross section. It is parabolically distributed along the height of the beam. The calculation formula (taking a rectangular cross section as an example) is τ = V * Q / (I * b), where τ is the bending shear stress at a point on the cross section (unit: Pa, N / m). 2 V is the shear force (in N) acting on the cross section, and Q is the static moment (also called the first moment, in meters) of the area outside the location of the stress point about the neutral axis. 3 For a rectangular section, Q = b * (h) 2 / 4 - y 2 ) / 2, where h is the cross-sectional height, b is the cross-sectional width, and I is the moment of inertia of the entire cross-section about the neutral axis (unit: m). 4 ).

[0055] In practical applications, this embodiment takes a non-standard customized single-extension telescopic fork as an example and performs calculations using the finite element method (the model needs to be simplified for ease of calculation). A similar method can also be used for double-extension telescopic forks.

[0056] 1. Model: Design input conditions: Load: 200KG, upper fork lifting size 800mm x 170mm, stroke 900mm left and right. Figure 3 As shown.

[0057] 2. Material Setting: 42CrMo is used as the material for the assembly. The parameters of 42CrMo are as follows: Figure 4 As shown.

[0058] 3. Add boundary conditions: Based on the working state of the assembly, set the bottom mounting surface of the assembly as a fixed constraint, apply a 2000N (200kg) load to the right end face, and set the conditions as follows: Figure 5 As shown.

[0059] 4. Mesh Generation: The assembly is meshed using a standard mesh setting, such as... Figure 6 As shown.

[0060] 5. Results Analysis 5.1 Displacement Contour Map: From Figure 7 The maximum displacement can be seen to be 6.93 mm.

[0061] 5.2 Stress contour plot: From Figure 8 It can be seen that the maximum stress is 168 MPa, which is less than the material's yield strength [930 MPa], and meets the design requirements.

[0062] 5.3 Strain contour plot: From Figure 9 The maximum strain can be seen to be 0.000135.

[0063] 6. Summary: Finite element analysis was conducted using 42CrMo as the material. The analysis revealed that the maximum displacement was 6.93 mm, the maximum strain was 0.000135 mm, and the maximum stress was 168 MPa, which is less than the yield strength of 42CrMo [930 MPa]. Furthermore, the yield strength of the material is more than five times the maximum stress, thus meeting the safety strength design requirements.

[0064] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0065] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for safety assessment of telescopic forks combined with finite element analysis, characterized in that, include: Load determination steps: Determine the loads that the telescopic forks will bear during operation, including at least permanent loads and live loads; Model selection and establishment steps: Based on the actual structure and working state of the telescopic fork, establish a finite element analysis model, wherein the finite element analysis model needs to comprehensively consider the shape and size of the telescopic fork, the support method and the material properties; Material setting steps: In the finite element analysis model, set material parameters for each component of the telescopic fork that conform to the actual working conditions; Steps for adding boundary conditions: Add boundary conditions to the finite element analysis model based on the actual working state of the telescopic forks; Mesh generation steps: The finite element analysis model is meshed using standard mesh settings; Results analysis steps: Run the finite element analysis model to obtain the displacement cloud map, stress cloud map and strain cloud map of the telescopic fork under a given load, and extract the maximum displacement, maximum stress and maximum strain data; Safety assessment steps: Compare the maximum stress obtained from the analysis with the yield strength of the material to ensure that the maximum stress is lower than the yield strength of the material and that the yield strength of the material exceeds the maximum stress by a predetermined multiple, so as to meet the safety strength design requirements.

2. The method according to claim 1, characterized in that: When determining the permanent load, the weight of the telescopic fork and the weight of the fixed attachment components are obtained by measurement or theoretical calculation and are used as the permanent load. The weight of the telescopic fork is calculated by multiplying the material density and volume, and the weight of the fixed attachment components is obtained by actual weighing or design parameters. When determining the live load, the live load is determined based on the maximum weight of the items stored, retrieved, or transferred in the actual application scenario of the telescopic forks; the maximum weight is obtained through customer-specified requirements, industry standards, or experimental tests, and a dynamic load factor is considered to cover the impact or vibration effects in actual working conditions. The permanent load and the live load are combined according to the most unfavorable working condition to form the calculation load, which is used as the input condition for the finite element analysis model.

3. The method according to claim 1, characterized in that: In the finite element analysis process, the stress and strain distribution of the telescopic fork steel structure are calculated, including: The steel structure of the telescopic fork is discretized into a finite number of elements, each of which is regarded as an independent small structure. The elements are connected by nodes to form an overall finite element model. The element type is selected as beam element, shell element or solid element according to the structural characteristics. For the beam structure characteristics of telescopic forks, either Euler-Bernoulli beam theory or Timoshenko beam theory is selected to establish a calculation model. Euler-Bernoulli beam theory is suitable for small deformation and linear elastic material conditions, while Timoshenko beam theory is suitable for conditions that consider the influence of shear deformation. Based on the actual working conditions, combine permanent loads and live loads to calculate the structural response under uniformly distributed load q or concentrated load P. Calculate the maximum deflection of a simply supported beam under a uniformly distributed load; calculate the bending normal stress at a point on the cross section; calculate the bending shear stress at a point on the cross section of a rectangular beam. Eigenvalue buckling analysis is performed on the compression member to obtain the critical load value; Calculate the critical load Pcr of the ideal compression member to ensure that the actual working load is less than the predetermined safety factor multiple of the critical load; Compare the calculated maximum deflection value with the limit specified in the design code; If the maximum deflection exceeds the limit, adjust the structural parameters or recombine the loads until the safety requirements are met.

4. The method according to claim 1, characterized in that, The establishment of the finite element analysis model includes: Based on the actual structural parameters of the telescopic fork, including the number of sections of the single or double extension fork body, the arrangement of the fork arms, the shape and size of each component and their connection relationship, a geometric model is constructed using 3D modeling software or finite element preprocessing tools. Based on the working state of the telescopic forks, the fixed constraint positions and kinematic pair relationships are defined, and the actual support is simulated through the boundary condition module; Assign material parameters to each component of the geometric model. The main structure uses 42CrMo steel, and its elastic modulus E, yield strength, Poisson's ratio and other parameters are input from the material handbook or experimental data. Define the interaction relationships such as sliding contact between forks and meshing contact between gears and racks, and set the friction coefficient; at the same time, simulate the transmission connection of components such as couplings and reducers through coupling or rigid body constraints; Non-critical details are simplified to improve computational efficiency, and the rationality of the model is verified through static balance verification or modal analysis to ensure that it can accurately reflect the actual force and deformation characteristics of the telescopic fork.

5. The method according to claim 1, characterized in that, Set material parameters for each component of the telescopic fork that conform to actual working conditions, specifically including: Based on the actual working conditions of the telescopic forks, including load type, operating frequency and environmental factors, 42CrMo steel was selected as the main structural material. Obtain the key parameters of 42CrMo steel through material handbooks, experimental tests or data provided by suppliers, and input them into the property definition module of the finite element analysis model. These key parameters include at least the elastic modulus E, yield strength, tensile strength, Poisson's ratio and density. For different components of the telescopic fork, corresponding material parameters are set according to their actual functions and stress characteristics; For components subject to plastic deformation or large deformation, enable the nonlinear material model in the finite element software and input stress-strain curve data to accurately simulate the material behavior under ultimate load. By comparing theoretical calculations with experimental test results, the accuracy of material parameter settings is verified, ensuring that the finite element analysis results can truly reflect the mechanical properties of the telescopic fork.

6. The method according to claim 1, characterized in that, Add boundary conditions to the finite element analysis model, including: Apply a fixed constraint to the bottom mounting surface of the assembly: Based on the installation method of the telescopic fork, a full-degree-of-freedom fixed constraint is applied to the bottom mounting surface of the finite element model to constrain all translational and rotational degrees of freedom in order to simulate the rigid connection between the telescopic fork and the base or equipment. Use a geometric coordinate system or node selection tool to accurately locate the mounting surface nodes and ensure that constraints are applied to the actual contact area. If there are multiple mounting points, local constraints should be applied to each mounting point separately to avoid stress concentration distortion caused by overall constraints. If elastic elements are present during actual installation, a spring-damping unit is inserted between the fixed constraint and the mounting surface, and the stiffness coefficient and damping coefficient are input to simulate the dynamic response characteristics of the flexible support.

7. The method according to claim 6, characterized in that, Add boundary conditions to the finite element analysis model, including: Apply loads to the right end face or other designated locations according to the actual load conditions: Based on the actual working scenario of the telescopic forks, the following types of loads are applied: Concentrated force: A vertically downward concentrated force is applied to the center node or key load-bearing point on the right end face of the telescopic fork to simulate the weight of the cargo or impact load. Distributed force: If the load distribution is uneven, apply a pressure load to the right end face and define the load gradient through the pressure distribution function; Torque load: Applying bending moment or torque to the rotating shaft or connecting parts of the telescopic fork to simulate the inertial force or external driving torque when the telescopic fork extends or rotates; If the telescopic forks are subjected to alternating loads, the time history load input curve of the load changing over time can be used, or a multi-level load cycle can be defined through the fatigue load spectrum to support fatigue life analysis.

8. The method according to claim 7, characterized in that, Adding boundary conditions to a finite element analysis model also includes: For the sliding joint of the telescopic fork, a sliding constraint is applied between the contact surfaces to restrict other degrees of freedom except for the direction of motion, and a friction coefficient is set to simulate actual transmission loss. For connections with gaps, set an initial gap or preload in the contact definition to reflect assembly errors or preload conditions; If the telescopic fork is dynamically coupled to other components, the finite element model can be connected to the dynamic model through rigid-flexible coupling or multibody dynamics interface, and dynamic parameters such as rotational speed or acceleration can be input.

9. The method according to any one of claims 1 to 8, characterized in that, The acquisition of displacement contour maps, stress contour maps, and strain contour maps of the telescopic fork under a given load includes: Displacement cloud map: Select the total displacement or displacement in a specified direction as the output variable; display the displacement distribution through cloud map coloring, set the color scale range and contour line interval to intuitively present the deformation trend of the telescopic fork; mark the displacement values ​​of key nodes and generate a 3D displacement vector map to show the deformation direction; Stress cloud map: Select equivalent stress or principal stress as output variable, set color scale range and contour line interval; for welded joints or stress concentration areas, enable local mesh refinement display and overlay stress gradient arrows to indicate high stress direction; generate stress extreme point markers and automatically label the location and value of maximum stress; Strain contour plot: Select equivalent strain or principal strain as the output variable, set the color scale range and contour interval; for plastic deformation regions, enable strain hardening curve overlay to display the strain-stress relationship to assess material damage; generate strain path tracing to record the strain variation curves of key nodes with time or load step.

10. The method according to any one of claims 1 to 8, characterized in that, Extract the maximum displacement, maximum stress, and maximum strain data, including: Maximum displacement extraction: Call the extreme value query function to automatically search for the maximum total displacement and coordinate position of all nodes in the model; output the maximum displacement value to a text file or Excel spreadsheet, and mark the corresponding load step and time point; generate displacement-time curves or displacement-load curves to analyze the variation law of displacement with external conditions. Maximum stress extraction: Locate the location of the maximum equivalent stress or maximum principal stress in the model using the stress extremum search function; extract the maximum stress value and its element number and material properties, and determine whether it exceeds the material yield strength σy; generate a stress concentration factor calculation report; Maximum strain extraction: The strain extremum analysis function is invoked to obtain the location of the maximum equivalent strain and the maximum principal strain; the strain value and its path are extracted, and it is determined whether the material fracture strain has been reached; strain-life curve data points are generated to provide input for fatigue analysis.

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