A forklift mast modeling method based on multi-body dynamics analysis

Abstract

The application provides a forklift mast modeling method based on multi-body dynamics analysis, relates to the technical field of computer-aided engineering, and comprises the following steps: a mast multi-body dynamics model is established; flexible treatment is performed on a lifting cylinder of the mast based on a flexible-flexible point line constraint mode; flexible treatment is performed on a contact area between a mast channel steel track and a roller in the mast multi-body dynamics model, rigid-flexible contact between the roller and the track is defined, and mutual contact force between the roller and the channel steel is simulated; the displacement of the cylinder is driven, and a mast rigid-flexible coupling multi-body dynamics model is obtained based on the flexible treatment result of the lifting cylinder of the mast and the flexible treatment result of the contact area between the mast channel steel track and the roller; the application solves the problems of forklift mast multi-body system dynamics modeling and dynamic simulation, improves the dynamic simulation and forward design capability of the forklift mast, and is universal and efficient in modeling method and high in calculation result precision.

Description

Technical Field

[0001] This application belongs to the field of computer-aided engineering technology, and specifically relates to a forklift mast modeling method based on multibody dynamics analysis. Background Technology

[0002] As one of the most important working devices of a forklift, the three-section fully free mast has a complex assembly structure, mainly including the outer mast, middle mast, inner mast, fork carriage, stop rack, lifting cylinder, chain mechanism, etc. The stress conditions of each component are complex, and the mechanical properties of the components (stiffness, strength, modal characteristics, etc.) are related to the overall performance of the mast system. At present, mast structural design and analysis usually adopts the component-level static strength verification method. First, based on the principle of force and moment balance, the stress relationship of the mast is calculated. Then, the static strength finite element analysis is performed on each structural component separately. Based on the dynamic load coefficient and material yield limit of the mast components under various extreme working conditions, it is determined whether the safety factor of the mast structural components meets the design standards. However, the actual operation of a forklift mast is complex, and the fatigue problems caused by dynamic loads cannot be considered in static stress analysis methods. Therefore, it is impossible to predict the impact of loads on the mast structure reliability during actual operation. In addition, the mast stress in static analysis is calculated under the assumption that the mast components are fully rigid, which cannot represent the stress state of the mast structural components in the system. Therefore, errors are inevitable in the calculation of structural stress values. Summary of the Invention

[0003] In view of this, the purpose of this application is to provide a forklift mast modeling method based on multibody dynamics analysis to solve the problem of designing forklift mast structures using static stress analysis.

[0004] The technical solution to the above-mentioned technical problems in this application is as follows:

[0005] This application provides a forklift mast modeling method based on multibody dynamics analysis, including:

[0006] Establish a multibody dynamics model of the gantry;

[0007] The lifting cylinder of the gantry is made more flexible based on the soft-soft point-line constraint method.

[0008] In the gantry multibody dynamics model, the contact area between the gantry channel steel track and the roller is made flexible, the rigid-flexible contact between the roller and the track is defined, and the mutual contact force between the roller and the channel steel is simulated.

[0009] The displacement of the hydraulic cylinder is driven, and based on the results of the flexible treatment of the lifting hydraulic cylinder of the gantry and the results of the flexible treatment of the contact area between the gantry channel steel track and the roller, a rigid-flexible coupled multibody dynamic model of the gantry is obtained.

[0010] Optionally, a multibody dynamics model of the gantry is established, including:

[0011] Define the topological relationship of the forklift mast, and establish a multibody dynamics model of the mast based on the topological relationship;

[0012] A two-dimensional rope model of the sprockets and chains of the forklift mast is established;

[0013] The components of the forklift mast are made more flexible.

[0014] Optionally, the process of making the components of the forklift mast flexible includes:

[0015] The inner gantry, middle gantry, and outer gantry are treated with flexible technology, and the inner gantry, middle gantry, and outer gantry are treated with mesh.

[0016] The connection between the gantry and the outside world is simulated using rigidly constrained rbe2 elements.

[0017] Optionally, the two-dimensional rope model establishes the lateral and longitudinal dynamic equations of the sprocket and chain through the state equations of the sprocket and chain.

[0018] Optionally, the lifting cylinder includes a piston cylinder and a piston rod, and the lifting cylinder of the gantry is made more flexible based on a soft-soft point-line constraint method; including:

[0019] Define soft-soft dot-line constraints;

[0020] The piston cylinder and piston rod are made flexible using the gantry multibody dynamics model, and the contact relationship between the piston cylinder and piston rod is simulated using the flexible point-line constraint.

[0021] Optionally, the definition of soft-soft dotted line constraints includes:

[0022] Both the piston cylinder and piston rod are constructed using second-order hexahedral units;

[0023] A row of nodes is arranged at equal intervals inside the piston cylinder and piston rod, and a soft-soft point-line constraint is defined by connecting them to second-order hexahedral elements through rigid constraint rbe2.

[0024] Optionally, the process of making the contact area between the gantry channel steel track and the roller flexible in the gantry multibody dynamics model, defining the rigid-flexible contact between the roller and the track, and simulating the mutual contact force between the roller and the channel steel includes:

[0025] Flexible modeling is performed on the channel steel track, and the contact surface of the channel steel track is constructed using second-order hexahedral elements.

[0026] The roller is rigidly modeled and no mesh is applied.

[0027] The cylindrical direction of the roller is discretized to obtain three points. Three spheres are then constructed with the three points as their centers. The contact between the spherical surfaces of the three spheres and the track surface is defined as the rigid-flexible contact between the roller and the track.

[0028] The embodiments of this application bring the following beneficial effects:

[0029] 1. A dynamic model of a three-section fully free gantry mechanism is constructed from a system-level perspective, elevating the static analysis at the component level to the dynamic analysis at the system level. Through fixed-interface modal synthesis, the outer gantry, middle gantry, inner gantry, forklift carriage, and lifting cylinders in the gantry system are condensed into mass and stiffness matrices to achieve flexibility. This solves the over-constraint problem in the multi-rigid-body dynamic model of the gantry system and is beneficial for addressing the symmetrical force distribution problem of the left and right tilting cylinders and the left and right lifting cylinders.

[0030] 2. Implement dynamic load identification technology for gantry systems to accurately simulate the dynamic forces of main rollers, side rollers, chains, cylinder supports, etc. under actual working conditions, and provide dynamic loads for dynamic strength and fatigue life analysis of key components.

[0031] 3. The overall deformation of the gantry system under full load and high cargo position was accurately analyzed, taking into account the influence of the structural rigidity of the inner gantry, middle gantry and outer gantry, the reserved clearance for main roller assembly, etc. on the system deformation.

[0032] 4. The amplitude and frequency of high-level swaying of the gantry system were precisely analyzed, and the factors affecting the amount of swaying were decomposed into the gantry components and their connecting parts.

[0033] 5. The contact force model between the roller and the channel steel rail in this application adopts the Hertz contact force model. This model automatically calculates the contact stiffness and damping based on the characteristics of the contact material (Young's modulus, Poisson's ratio, etc.), and can also consider the contact gap and friction. Compared with other contact algorithms, it is more efficient and has low requirements for computer hardware resources.

[0034] Other features and advantages of this application will be set forth in the following description and will be apparent in part from the description or may be learned by practicing the application. The objectives and other advantages of this application are realized and obtained through the structures particularly pointed out in the description, claims and drawings.

[0035] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings.

[0036] The advantages of this application in terms of its additional aspects will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a flowchart illustrating the forklift mast modeling method based on multibody dynamics analysis, as shown in the embodiments of this application.

[0039] Figure 2 The topological relationship of the three-section fully free gantry model shown in the embodiments of this application;

[0040] Figure 3 This is a finite element mesh model of the gantry component flexible processing shown in the embodiments of this application;

[0041] Figure 4 This is a finite element mesh model of the hydraulic cylinder component with flexible processing as shown in the embodiments of this application;

[0042] Figure 5 A flowchart illustrating the forklift mast modeling method based on multibody dynamics analysis is shown in the embodiments of this application.

[0043] Figure 6 The multibody dynamics model of the three-section fully free gantry system shown in the embodiments of this application;

[0044] Figure 7 The force and deformation cloud diagram of the three fully free gantry components shown in the embodiments of this application. Detailed Implementation

[0045] The technical solutions of the embodiments of this application 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 application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0046] Virtual prototyping technology based on multibody dynamics is particularly suitable for the dynamic analysis of a three-section fully free mast of a forklift. It can analyze the kinematic and mechanical characteristics of the mast system under the entire operating conditions. In addition to including the mass and stiffness characteristics of each component, the model can also simulate the assembly and connection relationships between components, and analyze the comprehensive mechanical characteristics of the mast as a whole from the perspective of the system. These characteristics mainly include the total deformation of the system, the load-bearing capacity at high positions, and the amount of sway. It can also obtain the dynamic loads of the mast structural components under actual operating conditions, and then decompose them to each component to carry out structural fatigue and reliability prediction.

[0047] Since static analysis of the gantry cannot meet the requirements of dynamic optimization design of the system, and most quality problems reported by the market cannot be solved by static analysis, this application mainly realizes the dynamic analysis of the gantry system, elevating component-level structural analysis to system-level dynamic analysis. This solves key technical problems in the dynamic design process of the gantry system, and is mainly applied to dynamic strength and fatigue analysis of gantry structural components, analysis of the impact of gantry system deformation on vehicle stability, analysis of gantry system swaying at high cargo positions, and impact dynamics analysis of the gantry system during lifting. Using multibody dynamics models to analyze and solve similar dynamic problems is particularly effective, systematically addressing persistent gantry system failures and improving the performance of the gantry and even the entire vehicle from a comprehensive perspective.

[0048] Example 1:

[0049] To facilitate understanding of the embodiments of this application, a forklift mast modeling method based on multibody dynamics analysis disclosed in the embodiments of this application will first be described in detail, such as... Figure 1 , Figure 5 As shown, it includes the following steps:

[0050] Step S1: Establish the gantry multibody dynamics model; the specific steps are as follows:

[0051] Step S1.1: Define the topological relationship of the forklift mast, and establish a multibody dynamics model of the mast based on the topological relationship;

[0052] In this embodiment, the association features between components are defined according to the topological relationship of the gantry system, fully representing the topological relationship of the three-section fully free gantry model, such as... Figure 2 As shown;

[0053] Step S1.2: Create a two-dimensional rope model of the sprockets and chains of the forklift mast;

[0054] Specifically, the two-dimensional rope model is established by using the state equations of the sprocket and chain to establish the lateral and longitudinal dynamic equations of the sprocket and chain.

[0055] The sprocket and chain mechanism in the gantry system is complex. This embodiment uses a two-dimensional parametric chain model to define its transmitted force load and motion. Compared with the complex three-dimensional chain multibody model, this improves the overall gantry model, modeling efficiency, calculation speed and reliability.

[0056] The sprocket and chain mechanisms in gantry systems are typically open chain mechanisms, resulting in complex system structures. Since the chain and sprocket are in contact, most multibody dynamics software offers 3D chain modeling techniques and uses recursive algorithms to solve the chain mechanism. However, this algorithm is less efficient than the finite difference method for the entire gantry system, and the model construction process for 3D chain modeling simulation is complex. Therefore, a two-dimensional parametric open rope model is proposed to replace the chain mechanism to simulate the transmission of loads and motion. The two-dimensional rope model establishes the transverse and longitudinal dynamic equations of the sprocket and chain elements through state equations, similar to the vibration equations of a string, and uses partial differential equations to describe the forces on the sprocket span. This model can consider the chain's extensibility, the mass of a single chain link unit, the Young's modulus and damping coefficient of the material, the chain's free length and tension, and the friction coefficient between the chain and sprocket. The modeling process is simple, which is key to the feasibility of multibody dynamics analysis of gantry systems.

[0057] Step S1.3: Make the components of the forklift mast flexible.

[0058] Specifically, the flexible treatment of the forklift mast components includes:

[0059] Step S1.3.1: Perform flexible technology processing on the inner gantry, middle gantry and outer gantry, and perform grid processing on the inner gantry, middle gantry and outer gantry;

[0060] Step S1.3.2: The connection between the gantry and the outside world is simulated using rigid constraint rbe2 elements.

[0061] Specifically, the inner gantry, middle gantry, and outer gantry are processed using a flexible technology based on contact analysis, and the inner gantry, middle gantry, and outer gantry are meshed. The meshing uses second-order tetrahedral elements or second-order hexahedral elements. The channel steel in contact between the roller and the rail uses second-order hexahedral elements. Except for the channel steel in contact between the roller and the rail, other gantry components use second-order tetrahedral elements. The transition between second-order hexahedral elements and second-order tetrahedral elements is achieved by node fusion.

[0062] Most components of the gantry system are designed for flexibility. Flexible techniques suitable for contact analysis are used for the inner, middle, and outer gantry. The meshes for these components are also standardized and processed. The component meshes are required to use second-order tetrahedral or second-order hexahedral elements. The channel steel portion where the rollers contact the rails must use hexahedral elements. Node merging can be used when transitioning between tetrahedral and hexahedral meshes. The connection between the gantry structure and the external environment is simulated using RBE2 elements. Figure 3 As shown;

[0063] The standardization and processing of meshes are existing technologies in finite element mesh processing. This application mainly considers the processing and standardization requirements of meshes from the perspective of modeling efficiency and computational accuracy. Without considering the modeling time cost, all components of the gantry can be meshed into hexahedral elements, but this will greatly increase the modeling difficulty and time. If only the channel steel part where the roller contacts the rail is used with second-order hexahedral elements, and other parts are used with second-order tetrahedral elements, and the transition part between second-order hexahedral elements and second-order tetrahedral elements is done by node fusion, and the specification requires the mesh size to be 3-10mm, this will reduce the modeling difficulty and scale, improve the computation speed, and effectively ensure the efficiency and accuracy of flexible component processing.

[0064] This embodiment constructs a three-section fully free gantry mechanism dynamic model from a system-level perspective, elevating component-level static analysis to system-level dynamic analysis. Through fixed-interface modal synthesis technology, the outer gantry, middle gantry, inner gantry, forklift carriage, and lifting cylinders in the gantry system are condensed into mass and stiffness matrices to achieve flexibility. This solves the over-constraint problem in the multi-rigid-body dynamic model of the gantry system and helps address the symmetrical force distribution problem of the left and right tilting cylinders and the left and right lifting cylinders. Simultaneously, it implements dynamic load identification technology for the gantry system, accurately simulating the dynamic forces of the main roller, side rollers, chains, and cylinder supports under actual working conditions, and providing dynamic loads for the dynamic strength and fatigue life analysis of key components.

[0065] In this embodiment, the Hertz contact force model is used to model the contact force between the roller and the channel steel rail. This model automatically calculates the contact stiffness and damping based on the characteristics of the contact material (Young's modulus, Poisson's ratio, etc.). It can also take into account the contact gap and friction. Compared with other contact algorithms, it is more efficient and has lower requirements for computer hardware resources.

[0066] Step S2: Based on the flexible-flexible point-line constraint method, the lifting cylinder of the gantry is made more flexible;

[0067] In specific implementation, the lifting cylinder includes a piston cylinder and a piston rod. Based on a flexible-flexible point-line constraint approach, the stiffness and deformation of the lifting cylinder are considered in the gantry multibody dynamics model. The lifting cylinder of the gantry is made more flexible, including:

[0068] Step S2.1: Define the soft-soft dot-line constraint;

[0069] The contact relationship between the cylinder barrel and the piston rod in a hydraulic cylinder is generally achieved through the piston and the cylinder wall. This contact is a surface-to-surface contact, which is computationally expensive. Using point-to-line contact as an approximation to replace surface-to-surface contact can greatly improve computational efficiency and also take into account the stiffness changes during the movement of the hydraulic cylinder. The point of point-to-line contact is the midpoint of the piston, and the line of point-to-line contact is the centerline of the piston rod.

[0070] In one feasible implementation, defining the soft-soft dotted line constraint includes:

[0071] Step S2.1.1: Both the piston cylinder and piston rod are constructed using second-order hexahedral elements;

[0072] Step S2.1.2: Arrange a row of nodes at equal intervals inside the piston cylinder and piston rod, and define a soft-soft point-line constraint by connecting them to the second-order hexahedral element through rigid constraint rbe2.

[0073] Considering the deformation of the lifting cylinder body and its constraint on the gantry deformation during the gantry lifting process, a special flexibility treatment technology is required for the lifting cylinder. The flexible piston cylinder and piston rod use a soft-soft point-line constraint to simulate their contact relationship. Both the piston cylinder and piston rod are constructed using second-order hexahedral elements, with a row of nodes evenly spaced inside. These nodes are connected to the hexahedral elements via RBE2 elements to define the soft-soft point-line constraint. RBE2 is a prerequisite for the soft-soft point-line constraint. In this constraint method, the points and lines need to be constructed with the master nodes in the rigid element (RBE2), such as... Figure 4 As shown.

[0074] Step S2.2: The piston cylinder and piston rod are made flexible using the gantry multibody dynamics model, and the contact relationship between the piston cylinder and piston rod is simulated by the flexible-flexible point-line constraint.

[0075] Specifically, the flexibility of the hydraulic cylinder is crucial in the multibody dynamics of the gantry. If the cylinder component is not flexible and remains a rigid body, it will constrain the deformation between the outer and middle gantry, causing the calculation results to deviate from reality. After the hydraulic cylinder is made flexible, its stiffness and connection relationship can be considered in the gantry system. The stiffness of the hydraulic cylinder changes with the lifting height, so special treatment is required. The steps are as follows:

[0076] Step S2.2.1: Define the center lines of the piston rod and the cylinder barrel. The length of these two center lines must be greater than their stroke.

[0077] Step S2.2.2: The centerline needs to be discretized into several equidistant points. The points are connected to the grid points of the cylinder through rigid elements (rbe2). These points and the mounting and fixing points of the cylinder constitute the set of condensed points in the fixed interface modal synthesis method, which participate in the mass and stiffness condensation.

[0078] Step S2.2.3: Connect the discrete points of the center line and the mounting and fixing points of the hydraulic cylinder in order of position to form line segments. These two line segments are used to define the constraint relationship between the piston rod and the hydraulic cylinder barrel.

[0079] Step S3: In the gantry multibody dynamics model, the contact area between the gantry channel steel track and the roller is made flexible, the rigid-flexible contact between the roller and the track is defined, and the mutual contact force between the roller and the channel steel is simulated.

[0080] Flexible treatment of components is a common technique in multibody dynamics analysis, typically achieved using modal synthesis with fixed interfaces. The modal set includes canonical modes in the free state and static modes under unit displacement conditions. Due to the unit displacement loading condition, the mast components must use rigid elements (rbe2) for external connections. Although this increases the local stiffness of the components and affects the accuracy of the analysis, this method is convenient for modeling and simple to handle, and is widely accepted as a requirement for engineering analysis. However, for multibody dynamics analysis of forklift mast systems, traditional flexible treatment techniques alone are insufficient. Two challenges are typically encountered in mast systems: first, the inner, middle, and outer masts requiring flexible treatment have both fixed connections and movable contact relationships with the external environment. Contact is a difficult aspect of flexible treatment, requiring consideration of factors such as solution speed, modeling efficiency, and computational accuracy. Researching point-to-surface contact techniques based on Hertzian contact is most suitable for handling the contact relationships of flexible mast components. The rollers and the mast channel steel rails... The contact definition is handled as follows: the surface of the gantry component in contact with the roller is treated flexibly. During mesh generation, it must be guaranteed to be quadrilateral. The quadrilateral surface is defined as the contact surface through a row and column structure. This definition method has the simplest contact surface element, and the search for the contact surface is efficient during contact calculation, which greatly reduces the calculation time. The roller in contact with the gantry is usually a cylindrical surface. The calculation speed of surface-to-surface and line-to-surface contact is very slow. Research has found that surface-to-surface and line-to-surface contact needs to be discretized. By discretizing it into several point-to-surface contacts, it is approximated as surface-to-surface and point-to-surface contact, which greatly improves the calculation efficiency. The second challenge in the flexible processing of gantry components is that the load acts on the two fork faces through the load center point. The connection between this load center point and the fork cannot be handled by traditional rigid elements (rbe2). Rigid elements are not suitable for handling distributed loads. Flexible elements (rbe3) can be used to define the connection relationship. However, flexible elements do not support the flexible processing technology of modal synthesis method with fixed interface. Research has found that in order to be compatible with the above two points, the connection points of flexible elements (rbe3) need to be removed from the static modal solution case under the unit displacement condition.

[0081] In one feasible implementation, the process of making the contact area between the gantry channel steel track and the roller flexible in the gantry multibody dynamics model, defining the rigid-flexible contact between the roller and the track, and simulating the mutual contact force between the roller and the channel steel includes the following steps:

[0082] Step S3.1: Perform flexible modeling on the channel steel track, and the contact surface of the channel steel track adopts second-order hexahedral elements;

[0083] Step S3.2: Perform rigid modeling on the roller, and do not mesh the roller;

[0084] Step S3.3: Discretize the cylindrical direction of the roller to obtain three points, and establish three spheres with the three points as centers respectively. The contact between the spherical surface of the three spheres and the track surface is determined as the rigid-flexible contact between the roller and the track.

[0085] Step S4: Drive the displacement of the hydraulic cylinder. Based on the results of the flexible treatment of the lifting hydraulic cylinder of the gantry and the results of the flexible treatment of the contact area between the gantry channel steel track and the roller, obtain the rigid-flexible coupled multibody dynamics model of the gantry.

[0086] Simulation comparison examples illustrate (software used: LMS Virtual.Lab)

[0087] This application demonstrates the advantages of relative static analysis methods, comparing the differences between multibody dynamics modeling and static equilibrium methods in analyzing the force relationships of gantry system sub-components. The multibody dynamics model of the three-section fully free gantry system is as follows: Figure 6 As shown, the forces are as follows: Figure 7 As shown.

[0088] This embodiment proposes a forklift mast modeling method based on multibody dynamics analysis, including: establishing a multibody dynamics model of the mast; flexibly processing the lifting cylinder of the mast based on a flexible-flexible point-line constraint method; flexibly processing the contact area between the mast channel steel track and the roller in the multibody dynamics model of the mast, defining the rigid-flexible contact between the roller and the track, and simulating the mutual contact force between the roller and the channel steel; driving the displacement of the cylinder; and obtaining a rigid-flexible coupled multibody dynamics model of the mast based on the results of the flexible processing of the lifting cylinder and the contact area between the mast channel steel track and the roller. This application realizes the dynamic analysis of the mast system, elevating the component-level structural analysis to the system-level dynamic analysis, and solving the problem of dynamic modeling and dynamic simulation of the multibody system of the forklift mast. It is mainly applied to the dynamic strength and fatigue analysis of mast structural components, the influence analysis of mast system deformation on the stability of the whole vehicle, the high-position sway analysis of the mast system, and the impact dynamic analysis of the mast system during the lifting process. This embodiment systematically solves the persistent problems of mast system failures, improving the performance of the mast and even the entire vehicle from a comprehensive perspective. This embodiment can also accurately determine the overall deformation of the mast system under full load and high cargo position, taking into account the structural stiffness of the inner, middle, and outer masts, as well as the pre-reserved clearance for the main roller assembly, on the system deformation. It can accurately analyze the amplitude and frequency of high-position swaying in the mast system, decomposing the factors affecting the amount of swaying to the mast components and their connectors. The method of this application improves the dynamic simulation and forward design capabilities of forklift masts; the modeling method is universal and efficient, and the calculation results are highly accurate.

[0089] The above embodiments are only used to illustrate the present invention. The structure, size, setting position and shape of each component can be changed. Based on the technical solution of the present invention, any improvements and equivalent transformations made to individual components according to the principles of the present invention should not be excluded from the protection scope of the present invention.

Claims

1. A forklift mast modeling method based on multibody dynamics analysis, characterized in that, include: Establish a multibody dynamics model of the gantry; The lifting cylinder of the gantry is made more flexible based on the soft-soft point-line constraint method. In the gantry multibody dynamics model, the contact area between the gantry channel steel track and the roller is made flexible, the rigid-flexible contact between the roller and the track is defined, and the mutual contact force between the roller and the channel steel is simulated. The displacement of the hydraulic cylinder is driven, and based on the results of the flexible treatment of the lifting hydraulic cylinder of the gantry and the results of the flexible treatment of the contact area between the gantry channel steel track and the roller, a rigid-flexible coupled multibody dynamic model of the gantry is obtained. The establishment of the gantry multibody dynamics model includes: Define the topological relationship of the forklift mast, and establish a multibody dynamics model of the mast based on the topological relationship; A two-dimensional rope model of the sprockets and chains of the forklift mast is established; The components of the forklift mast are made more flexible.

2. The forklift mast modeling method based on multibody dynamics analysis according to claim 1, characterized in that, The process of making the components of the forklift mast more flexible includes: The inner gantry, middle gantry, and outer gantry are treated with flexible technology, and the inner gantry, middle gantry, and outer gantry are treated with mesh. The connection between the gantry and the outside world is simulated using rigidly constrained rbe2 elements.

3. The forklift mast modeling method based on multibody dynamics analysis according to claim 1, characterized in that, The two-dimensional rope model establishes the lateral and longitudinal dynamic equations of the sprocket and chain through the state equations of the sprocket and chain.

4. The forklift mast modeling method based on multibody dynamics analysis according to claim 1, characterized in that, The lifting cylinder includes a piston cylinder and a piston rod. Based on a flexible point-line constraint approach, the lifting cylinder of the gantry is made more flexible, including: Define soft-soft dot-line constraints; The piston cylinder and piston rod are made flexible using the gantry multibody dynamics model, and the contact relationship between the piston cylinder and piston rod is simulated using the flexible point-line constraint.

5. The forklift mast modeling method based on multibody dynamics analysis according to claim 4, characterized in that, The definition of the soft-soft dotted line constraint includes: Both the piston cylinder and piston rod are constructed using second-order hexahedral units; A row of nodes is arranged at equal intervals inside the piston cylinder and piston rod, and a soft-soft point-line constraint is defined by connecting them to second-order hexahedral elements through rigid constraint rbe2.

6. The forklift mast modeling method based on multibody dynamics analysis according to claim 1, characterized in that, The process of making the contact area between the gantry channel steel track and the roller flexible in the gantry multibody dynamics model defines the rigid-flexible contact between the roller and the track, and simulates the mutual contact force between the roller and the channel steel, including: Flexible modeling is performed on the channel steel track, and the contact surface of the channel steel track is constructed using second-order hexahedral elements. The roller is rigidly modeled and no mesh is applied. The cylindrical direction of the roller is discretized to obtain three points. Three spheres are then constructed with the three points as their centers. The contact between the spherical surfaces of the three spheres and the track surface is defined as the rigid-flexible contact between the roller and the track.

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