Analyze product conceptual design and variant design technology, discuss the characteristics and existing problems of conceptual design and variant design concepts in the current intelligent CAD technology. According to the characteristics of relatively stable functional modules of agricultural machinery, low degree of structural complexity, and the advantages of intelligent CAD technology, taking the design of seeder as an example, an intelligent design system framework based on parameter design and assembly model is proposed. To solve the problems in agricultural machinery ICAD technology provides an effective way. With the development of industrial technology and fierce market competition, product replacement is getting faster and faster, and product design cycles are getting shorter and shorter. Modern CAD technology is also developing along the path of information integration, process integration, and enterprise integration. Traditional CAD technology is based on calculation and it is difficult to deal with symbol reasoning (plan design, evaluation, decision-making, structural design, etc.), and symbolic reasoning plays a decisive role in the design of agricultural machinery. Therefore, it is necessary to introduce artificial intelligence methods and adopt experts. System technology, the development of intelligent CAD (ICAD) technology to meet the requirements of creative design. ICAD is a complex system supporting product design that is organically integrated by multiple agents (or expert systems) and multiple CAD function modules [1]. ICAD technology mainly studies three aspects: design knowledge representation and modeling methods, knowledge utilization, and ICAD architecture. Conceptual design (or conceptual design) and assembly modeling to support variant design are two important aspects of ICAD technology. The introduction of ICAD technology in the design of agricultural machinery can solve the problems of repeated design and low utilization of information resources in agricultural machinery enterprises, shorten the product development cycle, and have enormous economic benefits and application prospects. The following first analyzes CAD theories, methods, and problems that currently support conceptual design and variant design: 1 Product Concept Design and Key Technologies Conceptual design is a mapping process from product development requirements to functional understanding. In order to complete the design process from demand to concept product solution, the product concept design must pass: demand analysis RA?? requirements formal RF identification, abstract problem IP? process decomposition PD?? functional decomposition FD?? sub-function decomposition SFD Functional element decomposition FED?? Principle solution Search SS?? Principle solution Combined SC? Program evaluation and other PE series of inference steps, the concept of product program CP. There are several characteristics in the concept design stage: 1 The product function information is the main processing object, and the function representation, maintenance, and reasoning are the core issues in the conceptual design stage; 2 The geometric information of the product is not complete, to represent incomplete geometric information, Transformation of the traditional geometric modeling method to represent the abstract geometric information; 3 For the entire design process, the design object as the design process continues to refine, requiring the CAD system to support progressive design and Top-down design; 4 functional information and The geometric information reflects different aspects of the design object, CAD system to solve the compatibility and mutual transformation relationship between these two technologies. The computer supports the conceptual design stage and mainly includes the following key technologies: 1.1 Product Information Modeling and Function Reasoning Technology In the existing CAD information modeling technology, geometric information occupies a dominant position. With the development of information modeling technology, this phenomenon is gradually changing. In modeling techniques that support conceptual design, functional information should dominate instead of geometric information. Because the object of construction of geometric information is a part, information can only be part of the part, and the function often represents the result of the interaction of more than two parts. In order to be compatible with the subsequent design process, geometric information is also essential in the product information modeling of the conceptual design stage. The integrated product information model at the conceptual design stage integrates functional, geometric and design intent modeling techniques. Its structural system is shown in Figure 1. In order to facilitate the design modification and variant design, the design intent modeling is also considered in the product information modeling in the conceptual design stage. The design intent records the thinking process of the designer, including the decomposition of the function to the function, the conversion of the function to the structure, and the process of solving the structural constraint. It describes how the geometric shapes and technical parameters that meet the design requirements are generated and determined. Ejij uses the DPDL language to model the design intent [2], using [][?] and []?{{} to record the state transitions. [] indicates the function, {} indicates the structure. 1.2 Integration of the design process Design is a gradual and iterative process. The CAD system supporting the entire design process should have the following characteristics: 1 To support Top-down design methods, follow-up designs must be based on sketches drawn from conceptual designs. In the subsequent design, the previous step design plan will become a constraint to promote the follow-up design. 2 The design intent reflects the entire historical process of the design object to some extent. Therefore, the inheritance of design intent information in the design process allows designers to adjust their design intent at any time for a part or structure, thus facilitating the modification and redesign. 3 To support the Top-down design approach, assembly-oriented modeling techniques are required. To support the entire process from conceptual design to detailed design, the geometric modeling techniques of different design processes should be compatible with each other. 2 CAD models and methods supporting variant design Variant design is a categorical definition of design methods and processes. It refers to the extraction of existing design and design plans, and specific modifications to produce a new product similar to the original design [3, 4]. Pahl and Beitz first divided the design into original design, adaptive design, and variant design, and pointed out that about 70% of practical design work is adaptive design and variant design. Variant design is so important that the CAD system can support this design method, but the CAD system's support for this design method is still very limited, so the theory and method of variant design has become a focus of CAD technology research. The main theories and methods that currently support variant design are: 2.1 Variant Design Theory Based on Assembly Model The current CAD system establishes the geometric model of the product from the part modeling. This method is difficult to express the functional information, assembly information and design intent of the product. Assembly modeling aims to establish a complete data model that describes product assembly information. It not only expresses part geometry information, but also reflects the functional requirements of the product and the designer's design intent through the assembly relationship between parts. There are two commonly used data models that describe the assembly relationships between parts: relational models and hierarchical models. The assembly model is in line with people's natural design process and is a good variant design method. In recent years, the assembly model and modeling method have been studied in-depth at home and abroad, but no complete theoretical system and practical modeling methods have been formed yet. 2.2 Modular variant design Modular design is based on functional analysis, and achieves a variety of base products and variant products through the combination of modules with the same functions and different uses. Modular design can greatly shorten the product design and manufacturing cycle, so that the product has greater flexibility and adaptability, so that the product has a strong market competitiveness. Modular design is based on the definition of modules and organization management. The division of specific product modules and the assembly relationship between modules and modules are predetermined and cannot be arbitrarily changed, thus limiting the scope of their use. 2.3 Feature-based variant design theory Feature design is the product-oriented design and manufacturing process. It is based on a geometric model and includes a product model scheme for parts design and production process information. It allows the designer to complete the design of the product by combining common shapes (such as grooves, ribs, bosses, keyways, etc.) instead of abstract points, lines, and faces. The system provides the ability to instantiate features with different attribute values. The commonly used shape features are provided by the system feature library, and many systems can also be extended by user-defined features. The development of feature technology provides a means for product variant design. The user achieves the purpose of product variant design by instantiating a series of features and automatically maintaining features. The problems existing in the feature technology: (1) The user design must use the system's pre-defined features to design the product, so that the conceptual design and technical design are completely limited by the processing method; (2) When the feature design is used for variant design, the general and parameterization are combined, but The interaction of features to the feature and the maintenance of the validity of the design process are fatal flaws in this approach. 2.4 Variant design based on parameter design and variable design Parametric design generally refers to the design of the structure of the object shape comparison, a set of parameters can be used to agree on the size relationship. The serialization and standardization designs commonly used in production fall into this category. The design of variables is that the modification of the design object requires more freedom, and the size and shape of the product are determined by solving a set of constraint equations. Parameter design and variable design are suitable for the initial design and final design of the product, so that the product design drawings can be automatically modified with the modification of some structural dimensions and environmental changes. In the design of variables, the Constraint Satisfaction Problem (CPS) must be considered. Designing an efficient constraint solver is a difficult task in variable design. At present, the implementation schemes of constraint-based variable design methods at home and abroad [5]: numerical constraint solving method of descending generation, rule-based geometric reasoning method and method based on construction process. 2.5 Variant design theory based on case-based reasoning Case-based reasoning (CBR) research at home and abroad is divided into two categories. The first is the design support system. The system is a browser that provides users with numerous examples and automatically selects some instances for users according to the new design requirements. Selection, instance modification is completed by user and system interaction. The other type is an automated design system that wants to find ways to automatically modify instances. The above variant design theories and methods all solve some important problems in the variant design to different extents and achieve certain objectives. Problems to be further solved: researching product data management techniques that can express design intent and supporting the entire product design process; providing effective organizational and management tools for existing product resources and multi-level deformation methods to make full use of the company's existing resources; Effective support for variant design of human-computer collaboration environment. 3 Characteristics of Agricultural Machinery Design Due to the current adoption of traditional design methods for agricultural machinery companies, the application of modern design methods lags far behind other industries such as aerospace and automotive. There are many repeated designs between agricultural machinery companies, and the utilization of enterprise information resources is low, resulting in miscellaneous agricultural product models. The degree of standardization is low, and the quality of products cannot be improved, which affects the efficiency of enterprises. Agricultural machinery design features: 1 There are many structural types and models. For example, in the design of planters, according to the classification of crop varieties and agronomic characteristics, there are seed drills, hole sowing machines and precision seed drills; according to the working principle, they are divided into mechanical seeders and pneumatic seed drills; according to the work width and matching Power can be divided into monomer seeders, 2 rows, 4 rows, 6 rows, 8 rows of seeders, etc.; 2 The functional structure is relatively stable and the structure is less complex. Planters generally include racks, ground wheels, transmission systems, seeding units, openers, fertilisers, soil coverings, and suppressors. Different types of seeders use different types of components and structural parameters, but products The function is basically the same. This structural stability is very easy to use modular modified design technology and parameter design technology; 3 The agricultural machinery test is influenced by seasonality and has a long research and development cycle. Using ICAD technology can shorten the product research and development cycle and save costs. 4 Intelligent Design Framework Based on Parametric Design and Assembly Model From the characteristics of the above-mentioned agricultural machinery enterprises, it can be seen that modular parameter design and variable design techniques based on case-based reasoning can greatly improve the design efficiency and design level of agricultural products and increase the competitiveness of agricultural products and enterprises. In this paper, an intelligent design framework based on parameter design and assembly model is proposed based on CBR technology, which provides a new idea for solving the problems in ICAD technology. The assembly model expresses and maintains design intent, product principles, and functions by establishing geometric models and assembly information between components. It is a product model that supports conceptual design and variant design. Case-based reasoning (CBR) solves certain problems in the past. The mature problem of the class problem is based on solving the similar problem and provides an effective method. The case base is the foundation of the organization's existing technology. The intelligent design framework based on parametric design technology and assembly model is shown in Figure 2. The system features: conceptual modeling and variant design methods are closely related; assembly model is the basis of case-based reasoning, CBR is the core of intelligent design system, assembly modeling is implemented in the CBR operation, making assembly model reuse a large number of existing resources . 5 Conclusion The CAD system must support the entire process of product design, resolve the compatibility and complementarity of conceptual design models and structural design models, and provide support for a large number of existing variant designs. Introducing ICAD technology in the design of agricultural machinery not only supports the three-dimensional design information model, but also researches the full-process product design model that supports two-dimensional design, transforms and rebuilds existing product information of enterprises, and improves the utilization of information resources. Intelligent design framework based on parametric design and assembly model provides an effective way to solve the problems in ICAD technology. The product data management and design process are closely integrated to improve the ability of the ICAD system to support conceptual design and variant design. references Dried Red Goji Berries,Organic Dried Red Goji Berries,Dried Sweet Red Goji Berry,Dried Red Goji Fruit Berry Ningxia ZhaiXianSong Commercial and Trading Co.,Ltd. , https://www.nxupin.com
Keywords intelligent CAD program design, variant design, parameter design
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