[Abstract]: Based on the study of the structural characteristics and production line design theory of non-tubular folding cartons, this paper realizes the parametric design of the planar structure diagram of non-tubular folding cartons. A folding carton structure diagram system was developed using AutoCAD as the platform and Visual LISP. The parametric design mainly adopts box type library technology, assisting in the design of some box element libraries. Keywords: Parametric design; Box type library; Folding cartons; Packaging CAD Currently, developed countries such as the United States and Japan are committed to the development of professional packaging design software. Computer-aided design has been widely used in the packaging industry, and relatively complete packaging CAD systems can be applied to all aspects of the entire packaging CAD process. China's packaging CAD technology started relatively late. Although professional box type design software is receiving increasing attention, its practical application is still limited. Based on this, this paper attempts to develop a simple yet accurate folding carton planar design software using AutoCAD as the platform and parametric design methods, comprehensively applying box type library and box element library technologies. 1 Parametric Design Parametric design refers to representing the dimensions of a parametric model using corresponding relationships, without needing to determine specific numerical values. Changing a parameter value will automatically alter all related dimensions and adhere to established constraints. Analysis of packaging boxes on the market reveals that most box structures fall into a few specific categories, differing only in size, decorative patterns, and packaging materials. Addressing these characteristics of packaging structure design, the folding carton structure design system employs a parametric design method. When developing a folding carton structure system using parametric design, users do not need to draw point-by-point with drawing tools, nor do they need to consider the relationships between dimensions or the issue of increasing or decreasing paper thickness. These quantitative relationships have already been considered by the designer. During the program, users only need to select and input the necessary parameters according to the program prompts; the drawing is completed automatically by the program. 2. Box Element Library Technology and Box Type Library Technology 2.1 Box Element Library Technology A complete box is generally composed of components such as a lid, bottom, flaps, and end plates, exhibiting a strong structural character, especially for tubular folding cartons. While the components differ for different complete box types, they generally share this hierarchical structure. The basic pixels constituting the end of the packaging box typically include line segments, circles (arcs), ellipses (arcs), and Bezier curves. For convenience, regular polygons, stars, hearts, and wavy lines can be added as basic pixels. These basic pixels form the basic box-shaped components of the packaging box, such as lid inserts, end flaps, and side flaps. Each basic box-shaped component constitutes a class, such as lid insert class, end flap class, etc. Each basic box-shaped component in a class has a different shape depending on the purpose, structural requirements, and aesthetics of the packaging box. Further, the basic box-shaped components are used to form combined components such as box lids and box bottoms, ultimately forming the overall box shape. 2.2 Box Type Library Technology Most packaging CAD systems, such as Founder Packaging, ArtiosCAD software, and BOX-VELLUM system, currently use box type library technology, which contains a database of a certain number of typical and complete box types. The box type library stores structural patterns of frequently used folding cartons. Using these typical box types for design can significantly improve design speed. Users only need to select the desired box type, input appropriate parameters such as length, width, height, and cardboard thickness, and the design result can be obtained in one operation. The box types can also be continuously expanded. Most tubular folding cartons can be divided into three parts: box body, box lid, and box bottom. The box body doesn't vary much, and the box lid and box bottom can be combined separately. Therefore, tubular folding cartons are suitable for using the box type library technology. For other non-tubular folding cartons, the box types have few similarities, making the use of a box type library unnecessary. Moreover, the software uses AutoCAD as a platform. After drawing the overall box type, if it doesn't meet the established requirements, its powerful drawing and editing functions can be used to modify it, compensating for the shortcomings of the box type library. 3 Development of Folding Carton Structure System 3.1 System Development Tools Among many development software programs, using AutoCAD for secondary development is a quick method. AutoCAD provides a complete, high-performance, object-oriented CAD program development environment, offering developers a variety of new choices. Its secondary development tools are constantly being updated, such as Auto LISP, Visual LISP, ADS, ARX, VB, VBA, and Visual Java. This article uses Visual LISP as an example. 3.2 System Flowchart The data flow of the folding cardboard box system runs through the entire system operation process, as shown in Figure 1. 3.3 Variable Naming and Coding For cardboard box structure design, almost every cardboard box uses variables for its length, width, height, and cardboard thickness. During development, the common method used in folding cardboard box structure design is used: length, width, and height are represented as L, B, H, and T. When writing code, variables are named using lowercase letters: l, b, h, and t. The base point of the cardboard box structure diagram is represented by Pt. The system adopts the same coordinate system as AutoCAD: the two-dimensional plane where the screen is located is the x-y plane, using a Cartesian coordinate system, with the origin located at the lower left corner of the screen. Based on the concept of parametric design, after the cardboard box design in Figure 2 is completed, the user only needs to input different parameter values ​​to obtain a series of structural diagrams with similar shapes but different sizes. System operation example: To design a general tray-type folding cardboard box with a length of 100mm, width of 80mm, and height of 50mm, and setting the cardboard thickness to 1mm with no other structural requirements, run the system. You will see an additional "Cardboard Box" menu in the menu bar. Clicking the menu will bring up 5 sub-menus. Select the "Traditional Box" sub-menu or the "Traditional Box" icon on the toolbar to enter the tray-type box drawing module. 4.1 Box Type Selection: Select the "Cardboard Box" menu shown in Figure 3 or the "Traditional Box" in the "Cardboard Box" toolbar. The "Traditional Box" module image menu shown in Figure 4 will pop up. Select a suitable name for the tray-type folding cardboard box or the 3D preview image on the right (in this example, a general tray-type box is selected). Click the "OK" button to enter the drawing process for the "General Traditional Box". 4.2 Parameter Input: After entering the "General Traditional Box" drawing program, the tray-type box parameter design dialog box will pop up, as shown in Figure 5. In the left-hand base point section, users can directly enter the values ​​of the x and y coordinates in the input boxes, or click "Pick Point <" to hide the dialog box. The dialog box will automatically pop up after the user selects a suitable base point on the screen with the mouse, allowing the user to set and modify other parameters. The newly opened dialog box displays the default values ​​for the box dimensions. Users can modify the basic parameters of the tray box—length, width, height, and paper thickness—as needed (in this example, there are also special parameters, such as the length of the top of the box and the height of the middle section). The system was designed with various problems and potential errors in mind, incorporating error handling. For example, if the user sets a parameter value to a negative value in Figure 5, the system displays an error message at the bottom of the dialog box. Users can modify the input based on the error message, and after confirming the correct input, the system will output the unfolded plan view of the box. 4.3 Drawing the Box Plan View After confirming that the parameters in the dialog box in Figure 5 are appropriate, the user clicks the "OK" button. The system automatically draws the plan view of the folded box at the user-selected base point, as shown in Figure 6. If the drawing does not meet the user's requirements, the user can use AutoCAD's drawing and editing functions to continue to modify the output drawing. 5 Conclusion (1) The folding carton system adopts a parametric design method. The length, width, height, cardboard thickness, and base point coordinates of the carton are set as the basic parameters of the carton. They are used to represent the vertices in the structural drawing, and then connected with appropriate line types to draw the carton structural drawing. By setting the parameters to different values, some structural drawings with similar shapes but different sizes can be obtained. (2) The system uses AutoCAD as a platform for secondary development, mainly based on box type library technology, combined with some box element library technology. This not only realizes the rapid and accurate drawing of the carton structural plan, but also increases the number of box types, greatly saving design costs and design time. (3) Considering the trend of packaging CAD/CAM integration and digital workflow, it is required that the folding carton structural drawing system improve the interface with packaging CAM equipment in future development to provide conditions for its widespread application in the packaging industry. The severe situation of international competition requires us to develop a packaging CAD system with independent intellectual property rights, effectively improve the production efficiency and competitiveness of China's packaging industry, and make China's packaging enterprises stand invincible.