Safety Analysis of Small Rail Roadway Stacker Based on Parametric Design

Abstract

The small rail roadway stacker is the core equipment of the automated three-dimensional warehouse. Its design directly affects the development trend of the logistics industry, enterprise production efficiency and economic benefits. In this paper, a parametric model of the small rail roadway stacker is developed using the parametric design method, according to the working principle and load-bearing. The safety of the small-sized tracked roadway stacker in three working states is analyzed using the finite element method, according to the working conditions and stress conditions of the small rail roadway stacker. Consequently, it is deduced that all the safety parameters meet the design requirements in the limit state. Moreover, the SolidWorks and ANSYS Workbench software are used for secondary development, while C# is used to compile the parametric design software of the small rail roadway stacker, which integrates the functions of three-dimensional model design, engineering drawing generation and finite element security analysis into a program software. Furthermore, by the visual parameter setting and command operation, the program background automatically calls the design software for design and safety analysis. Finally, the example verifies the efficiency of the parametric design software for the small rail roadway stacker.

1. Introduction

As the core equipment of intelligent logistics and automated three-dimensional warehouse, the stacker’s design directly affects the development trend of logistics industry and the production efficiency of enterprises [1,2,3]. The small rail roadway stacker is developing towards multi-type, high-speed and intelligent direction [4]. leading the progress in the field of logistics equipment. The parametric design is based on the algorithm thinking process. It expresses the structural characteristics or shape and size of the design object in the form of parameters, then links these parameters to establish the topological relationship between the design intention and the design response [5]. Compared with the traditional design method, the parametric design method undergoes great changes in both the way of thinking and the way of working. This can enrich the form of products, so as to meet the diversified and personalized requirements of the customers.

Several studies tackle the parametric design of stacker. For instance, Wang Dongsheng [6] analyzes the parametric design of stacker based on the SolidWorks platform, and develops efficient design input and file output steps. Gan Zhongping et al. [7] propose the combination of the PDM technology for module data management of stacker function modules, in order to achieve the product configuration design. Song Zhangling et al. [8] design a stacker parameterization system which combines SolidWorks and VB, according to the theory of modular design and serialized design. Wei Feng et al. [9] focus on the product case model construction technology, knowledge base construction technology and 3d model-driven engineering drawing adjustment technology, in order to develop a stacker design system. Wang Songtao et al. [10] construct a rapid design system of laneway stacker using VB as development tool and SolidWorks as development platform. These studies show that the current parametric design thinking is still stuck in the component design level, which cannot meet the design and production requirements of the current main products, and therefore fails to fundamentally solve the problems of repetitive drawings, low design efficiency and long design cycle.

In order to ensure that the stacker can be used in practice, it is necessary to efficiently analyze the safety of the stacker in its design process. Chen Jie et al. [11] use the ANSYS Workbench to perform a mechanical analysis on the cargo fork of the double column stacker and optimize the cargo platform mechanism. Zheng Yuqiao et al. [12] use the finite element analysis method to perform modeling and statics analysis of single column stacker, which greatly improves the column stiffness and stacker performance, while reducing the manufacturing cost. Huang Chao et al. [13] use ABAQUS to perform a static analysis and modal analysis on the model of small rail roadway stacker. In addition, they theoretically verify the rationality of the design scheme. Fu Cunyin et al. [14] use ANSYS to analyze the column deformation of stacker and obtain the dynamic curve and vibration curve of column deflection deformation changing with stacker operation time. From these studies, we can infer the current status: the current finite element analysis of the stacker is a modeling analysis of the already designed individual product, and there is no real-time, relevant safety analysis of the serialized design of the stacker. The research method of this paper is as follows. Firstly, the working state of small roadway stacker is analyzed and the parameter model is established. Next, determine the parameters that affect the fatigue strength during the stacker operation. Finally, combined SolidWorks, Workbench and programming control for secondary development. The purpose of this paper is to establish a multifunctional safety analysis software for small track road stacker which integrates the functions of model building, safety analysis and screening. The software can ensure the efficiency and safety of stacker design.

2. Working Condition Analysis of Small Rail Roadway Stacker

2.1. Safety Analysis Factors of Small Rail Roadway Stacker

The stacker requires a precise positioning during operation, in order to complete the access of goods. However, it is prone to deformation due to its large horizontal and longitudinal ratio. During operation, once the frame is deformed, it is easy to have inaccurate positioning of goods, and even the fork cannot normally enter and exit the goods. In addition, there is friction and collision with the shelf, which results in damage to the shelf and the stacker. In the case of emergency stop and power outage of the stacker, the strength of its column and the protection of goods should also be fully considered [15]. Therefore, in order to ensure stable operation and accurate positioning of the stacker, it is necessary to analyze its overall stress, safety factor and total deformation. The stacker in the running process requires frequent start, stop, acceleration and deceleration, so the stacker pillar is frequently affected by the alternating load. As the accumulated damage in a part of the structure or material reaches a certain level, the generated microscopic cracks will further expand to fracture even if the alternating load is less than the yield limit of the material, resulting in fatigue damage. According to the linear fatigue cumulative damage theory, the material will absorb quantitative static work in each cycle. When the absorbed static work accumulates to a certain amount, fatigue damage will occur to the workpiece [16]. Therefore, a fatigue life analysis of the workpiece is required.

This analysis shows that the stacker is mainly affected by the deformation of the frame, column and other structures, as well as the influence of cracks when the material reaches the yield limit.

2.2. Load Analysis of Small Rail Roadway Stacker

After the operation of the stacker, it is accompanied by frequent acceleration and fast braking. Therefore, it should be considered whether there are potential safety hazards in the operation process, such as the collapse caused by the transportation of goods, for example. Consequently, in the stacker working process in three-dimensional warehouse, the speed increasing stage, uniform speed stage and speed decreasing stage in the process of movement should be analyzed. The deformation, strength and stiffness of the stacker frame under full load operation should also be considered. In addition, the deformation, strength and stiffness of the column, loading platform and lower beam should be considered, when the stacking platform takes out the goods on the top shelf and accelerates forward and decelerates to stop. A high-speed operation is used to improve the work efficiency when away from the target position. In order to reduce the energy consumption, the stacker operates at a uniform speed when it reaches a suitable position, and ensures smooth deceleration when the distance is relatively close. On the other hand, studying the dynamic characteristics of the stacker structure can improve its positioning accuracy and stability.

In this paper, the small rail roadway stacker designed in the work of the maximum weight of access goods has 8 kg, with a maximum lifting height of 2 m, a movement distance of the pallet fork of 315 mm, and an acceleration of horizontal walking of 1 m/s². Due to the fact that the acceleration of the vertical lift of the stacker and expansion of cargo fork is very small, the force analysis and strength check are not carried out in this aspect.

According to this situation, the working condition of the small rail roadway stacker is shown in Figure 1.

The static load analysis of the stacker of small track roadway is first performed. According to the force analysis in Figure 1, the load distribution of the column mechanism of the stacker can be summarized as follows. The upper beam mechanism is symmetrical to the column, and its own gravity acts on the top of the column mechanism, which can be directly replaced by force F₁. The fork mechanism is placed on the side of the column mechanism, and the gravity of the fork mechanism and the goods it carries should be equivalent to force F₂ and torque M₁. The electric control cabinet is fixed on the other side of the column mechanism, and its gravity should be transformed to force F₃ and torque M₂. The column mechanism’s own gravity is expressed by F₄. Figure 2 presents the loading diagram of the transformed column mechanism.

The maximum deformation of column mechanism ω is computed as:

$$\left|\omega \right|=\left|M_1{\mathit{L}}_{\mathbf{2}}{}^{\mathbf{2}}/2EI\right|$$

(1)

where:

$M_1$ is the equivalent bending moment of gravity of cargo fork mechanism and its load in kN·m,

${\mathit{L}}_{\mathbf{2}}$ represents the distance between the fork and root of column mechanism in m,

$E$ represents the elastic modulus of material in Mpa,

$I$ is the moment of inertia of column mechanism such that I = (d⁴ − d₁⁴₎/12.

According to Equation (2), the maximum deformation of column mechanism is set to ω = 0.78 mm, which does not affect the use accuracy of small rail roadway stacker.

The maximum bending moment of the walking mechanism is expressed as:

$$M_{max}{=F}_{RB}{L}_5/{2+M}_3$$

(2)

Based on the calculation of the maximum bending stress of traveling mechanism, σmax is equal to 9.5 MPa, which is far less than the allowable stress of Q235 material (sigma). Similarly, the load analysis of the stacker under acceleration and deceleration state shows that the column mechanism is also affected by the inertia force.

Table 1. The bending stress and deformation of small rail roadway stacker.

/	Maximum Bending Stress σ (MPa)	Maximum Deformation ω (mm)
Static state	9.5	0.78
Under acceleration	10.3	1.48
Under deceleration	8.6	0.65

shows the maximum bending stress and deformation in each state. It can be seen that all the data meet the safety requirements.

The stacker frame is checked for strength and stiffness, and the obtained value only represents part of the stacker’s strength and stiffness. In addition, when the body is designed and checked, it is usually considered as a rigid body. Therefore, it is difficult to take into account the dynamic characteristics of the stacker and the vibration characteristics of the frame under the high-speed operation at full load, which greatly reduces the original precision, production efficiency and service life of the stacker. The deformation and force of the column, lower beam and loading platform, under static and full load acceleration and deceleration of stoner, can be displayed in a more intuitive way using the finite element method. The traditional empirical design method cannot meet the requirements of the high-performance stacker, and the development of a parametric stacker analysis system is required.

3. Modeling and Interface of Stacker Crane with Parameterized Operation

3.1. Modeling of Small Rail Roadway Stacker

The first step in the parametric design consists in building a model. The model building requires a piece of software with powerful design functions and rich interface technology, which can be directly imported into the ANSYS Workbench without changing the model file format, so as to facilitate the subsequent performance analysis and parametric programming of the small road-stacker. SolidWorks meets these requirements. Therefore, it is used as modeling software in this paper. In order to facilitate the subsequent parametric programming, the following principles are followed during modeling:

(1)

When modeling the parts, their structural characteristics should be first analyzed in order to determine the modeling sequence. The features of the models should be as simple as possible, and without too many parameters. Constraints or functional relations should be added in order to restrict the models. Serialization parameters are then added to the parts related to performance parameters (column in the column mechanism module, machine body in the walking mechanism module, and lower fork plate in the cargo fork mechanism), and a part design table is established.

(2)

In the assembly of parts, the assembly sequence and relative position relationship should be analyzed. The assembly of the internal parts of each module is first performed. Equations are then added to the sizes associated with the equation design, in order to form a corresponding relationship between the sizes. After the assembly of each module is completed, the whole assembly should be uniformly performed.

According to these principles, the module of the base stacker comprises of a top beam mechanism module, walking mechanism module, column mechanism module, control system module, fork mechanism module and lifting mechanism module. Figure 3 shows the corresponding assembly. Through this design and modeling, a complete parameterized operation model of small rail roadway stacker is developed. It lays a foundation for the safety analysis of stacker and design of parameterized software.

Modeling is divided into several modules: the top beam mechanism, walking mechanism, column mechanism, control system, pallet fork mechanism and lifting mechanism modules. Through this analysis, design and modeling, a complete parameterized operation model of small railroad aisle stacking crane is developed, which lays a foundation for the safety analysis of stacker and design of parameterized software.

3.2. Software Development and Modeling Interface

This paper aims at designing a computer aided design system for small roadways stacker, which includes design, modeling, engineering drawing and analysis. This system allows to perform the rapid design including the safety analysis by selecting the performance parameters of small track roadways stacker, and generates engineering drawings that can be directly used in production. Two main forms of secondary development exist. The first one is integrated into the original software in the form of AddIn plug-ins, while the second one independently runs in the form of EXE independent software [17,18]. This system involves the design of two software, SolidWorks and ANSYS Workbench, and finally combines their respective functions to generate an EXE executable software. This makes the software run more stable, even if the development software problems will not affect the use of the SolidWorks and ANSYS Workbench software, which is ideal for commercial companies. SolidWorks secondary development mainly performs software and model driving as well as other operations by calling API functions, which has a high compatibility [19]. Therefore, a clear understanding of SolidWorks API functions plays a crucial role in the subsequent SolidWorks secondary development process.

Table 2. Structure and functionality of the SolidWorks API.

Object	Structure of Hierarchy	Function
SldWorks	The object at the top	Provides methods to access all other SolidWorks API
ModelDoc	Child object of SldWorks	Properties and methods of different document models
PartDoc	Child objects of ModelDoc	Part model file
AssemblyDoc	Child objects of ModelDoc	Assembly model file
DrawingDoc	Child objects of ModelDoc	Project drawing document
Feature	Child object of DrawingDoc	Feature of representation
Sketch	Child object of DrawingDoc	Sketch of representation
Environment	Child object of SldWorks	Representing the environment
AttributeDef	Child object of SldWorks	Attribute definition
Modeler	Child object of SldWorks	Model Management

lists the structure and functions of the API. The SldWorks object is the highest level of all objects through which the connection between the secondary development plug-in and SolidWorks applications can be established. ModelDoc objects, PartDoc objects, PartDoc objects, etc. are specific methods under SldWorks objects to achieve detailed operation of model files and other functions. More precisely, it greatly reduces the development time and improves the development accuracy.

ANSYS mainly provides four secondary development tools: APDL (ANSYS Parametric Design Language), UPFs (User Programmable Features), UIDL (User Interface Design Language), Tcl (Tool command language). APDL is a parameterized design scripting language, which allows the users to organize operation commands in series without repeating input or output data between different software, thus performing the whole process of finite element analysis. The secondary development mode of ANSYS Workbench and SolidWorks and some required functional relations have hierarchical subordination, as shown in Figure 4.

As the assembly of the stacker is commonly used in point-line-plane assembly, the assembly relationship between different parts is relatively fixed. Therefore, the system uses the top-down design method of SolidWorks to assemble the parts of the small rail roadway stacker. The parameters are then set by the software to form a modification environment, in which the total assembly of the small rail roadway stacker is considered as the whole when the 3D model is reset in the background driven by the program. The parameters resetting mainly consists in changing the size of the parts. It only requires a simple adjustment of the assembly of individual parts. Consequently, the program-driven SolidWorks model design does not require to re-assemble the model, which simplifies the development.

3.3. Interference Check of the Model

The stacker model is composed of several heterogeneous 3D models, that are the top beam mechanism, walking mechanism, column mechanism, control system, fork mechanism and lifting mechanism modules. In the model design stage, a crucial problem consists in verifying the assemblability between the module models and discovering their interference. On the one hand, it can verify the correctness of the design and improve its quality. on the other hand, it can obtain the interference information of the interference parts and between the parts, which can efficiently guide the modification of the design [20].

The program-driven model performs static interference checking mainly through the parts. The ToolsCheck Interference method in the API is used for identification. The operation trajectory of the automatic interference check is coherent with the trajectory of the manual operation mode. The interference check is mainly performed in the general assembly of the small rail roadway stacker. A top-level assembly is first performed. It is then crossed again, layer by layer, until the lowest assembly is found. Afterwards, an interference check is performed on it using IsNothing (vIntCompArray) and IsNothing (vIntFaceArry) commands, in order to determine whether an interference exists. The dynamic interference check requires to move the position of the model according to the working process. In addition, a static interference check is performed on the position of each stage after moving, and it cannot destroy the assembly relationship of the parts. The model of small rail roadway stacker mainly requires a dynamic interference inspection of the structures which should be displaced in the work engineering, such as the assembly of the module of fork mechanism and the total assembly, for example. The specific process is shown in Figure 5.

4. Safety Analysis of Small Rail Roadway Stacker

According to the working condition analysis of the small rail roadway stacker in static state (cf. Figure 1), constraints and loads are added to the finite element model in the ANSYS Workbench. The two travelling wheels are then fixed. Considering that the user may be overloaded in the process of use, the vertical downward pressure of 125% of the rated load is applied to the fork mechanism. The chain fastener in the lifting mechanism is subjected to a vertical upward pull equal to its own gravity, while the supporting sprocket in the lifting mechanism is subjected to a pressure equal and opposite to that applied to the chain fastener. In addition, a gravitational field is applied to the environment in which the model is located.

The load and constraints are presented in Figure 6a. The equivalent stress cloud map, drawings of partial enlargement, phase change cloud map and stress safety factor cloud map are obtained by solving the loaded small rail roadway stacker model, as shown in Figure 6.

It can be seen from Figure 6a that the maximum stress of the basic type of small rail roadway stacker model under static state is almost 65 Mpa, at the connection between the column mechanism and walking mechanism modules. It can be observed from Figure 6b that the maximum deformation displacement of the basic type of small railroad aisle stacking crane model under static state occurs at the regulating wheel of the upper beam, which is almost 0.4 mm. As can be seen from Figure 6d, the minimum stress safety factor of the small rail roadway stacker model in the static state is generated by the connection between the column module and the walking mechanism module, and its stress safety factor is almost 3.8. The stress safety factor should consider the load, mechanical properties of materials, the difference between the test value and the design value and the actual value.

Similarly, the acceleration state and deceleration state of the model are analyzed. Subsequently, the results obtained under different states are analyzed, and the data are shown in

Table 3. The parameters of stacker model in various states.

/	The Acceleration (m/s2)	Maximum Stress (Mpa)	Maximum Deformation Displacement (mm)	Minimum Stress Safety Factor	Minimum Fatigue Life (Times)	Minimum Fatigue Safety Factor
The static situation	0	65	0.4	3.8	/	/
The accelerator	1	102	1.1	2.4	3.1 × 106	1.1
State of deceleration	−1	61	0.3	4.1	/	1.2

.

5. Software Development Example of Small Rail Roadway Stacker Design System

The stacker design software system is prepared according to the steps shown in Figure 7. The system interface design mainly includes a basic function interface, parametric design interface and security evaluation interface. The reconstruction of the parameterized stacker model mainly includes the whole model reconstruction, split model reconstruction and interference check. Generating engineering drawing mainly includes the adjustment of parts drawing and assembly drawing. The finite element analysis of the stacker mainly includes the analysis of the stress, strain, safety factor and low cycle fatigue of the stacker under three working states. Generating the analysis report mainly includes the acquisition of analysis value and analysis image.

This paper uses C programming language to invoke the command flow files and some custom script files to achieve the automatic analysis of the model in order to realize the secondary development of ANSYS Multiphysics. APDL language is used in the process to program the command flow files of the finite element analysis of small roadway stacker. The command flow files include the dsstringtable.xml file, which is used to complete the string registration and generate the ID that associates the specified event with the button; the DSMunueWrap.js file, which is used to represent the response events of button; the dstoolbar.xml file, which is used to control the display position and icon of the button.

Enter the set parameters in the software for calculation, and the obtained results are displayed in the tree menu bar on the left. The engineering drawing interface is shown in Figure 8a. After the model is generated, the corresponding engineering drawing can be selected from the left tree menu bar. The analysis results are presented in Figure 8b. The latter can clearly express the analyzed data and picture information, and achieve the expected results. The maximum stress of this type of stacker is far less than the yield strength. In addition, the maximum total deformation is within the working accuracy range. The minimum safety factor is higher than China’s safety factor of lifting machinery (1.9). The estimated life expectancy is 7.1 years. The minimum fatigue safety factor is coherent with the structural safety value.

6. Results

According to the data analysis, as shown in

Table 4. The parameters of a software development instance.

/	Maximum Stress (Mpa)	Minimum Stress Safety Factor	Maximum Deformation Displacement (mm)	Minimum Fatigue Life (Times)	Minimum Fatigue Safety Factor
Stacker parameters	102	2.4	1.2	3.1 × 106	1.1

, the maximum stress (102 Mpa) is generated at the connection between the column module and the walking mechanism module under the accelerated state. Note that this maximum stress value is far less than the yield stress of the Q235 material, which is equal to 235 Mpa. The minimum safety factor is almost 2.4, which is also generated at the connection between the column module and the walking mechanism module. According to the mechanical manual, the safety factor n of the lifting machinery is greater than or equal to 1.9, which meets the strength requirements. The maximum displacement of deformation is 1.2 mm, which meets the accuracy requirements. The minimum fatigue life is 3.1 × 106 times, which can work for 7.1 years based on the calculation of transporting 1 piece of goods per minute, and working 12 h a day or 300 days a year. The minimum fatigue safety factor of 1.1 (>1) indicates that the structure is safe.

7. Discussion

It can be deduced from the analysis of the deformation position that the maximum deformation displacement of the basic small rail roadway stacker model in different states, occurs at the regulating wheel of the upper beam. The deformation has a higher extent under acceleration, but within the accuracy allowed by its operation.

It can be deduced from these results that the analysis data of the basic small rail roadway stacker are at the maximum value in the acceleration state. Consequently, the stacker can meet the design requirements in strength, accuracy and service life. The software which can screen the stacker that meets the requirements, can then be developed.

Fully driving the whole model should meet the driving requirements of each parameter. For the stacker of track roadway, the number of dimensions will reach tens of thousands, and the workload of programming and calculation is large. Therefore, it is necessary to design a software, independent structure analysis, model selection and safety analysis of other types of small rail roadway stacker. Based on the analysis, the relevant model should be imported, and the macro code generated during each step of base analysis should be used. Afterwards, the corresponding parameters should be modified, and the APDL statement that failed to generate the macro code step for analysis should be added.

8. Conclusions

According to the working principle and bearing capacity of each module of the stacker, this paper considers the maximum lifting height, maximum lifting mass, horizontal traveling speed and travel of cargo fork as the main parameters of the small stacker with track roadway. More precisely, the main factor of safety and the size driving design are carried out in order to develop the parameterized model of the main parts. The parameterized model of the whole small track roadway stacker is then associated.

The force analysis and strength check of the main force module of the base type of small track roadway stacker, are also performed. The ANSYS Workbench software is used to conduct a finite element analysis of small track roadway stacker under static, acceleration and deceleration working states. In addition, the maximum stress, maximum deformation deviation, minimum safety factor, minimum fatigue life and minimum fatigue safety factor under each working state, are obtained. Moreover, the finite element analysis data under the three working states are summarized. It is deduced that all the parameters of the model in the limit state meet the design requirements.

Furthermore, the parametric design software system of the small track roadways stacker is developed. The example demonstrates that the software normally runs. Finally, the obtained results of the parametric model are obtained, the safety analysis is performed, and the expected effect is achieved.