Application of Object-Oriented Method in Modeling of Special CAD System

With the increasingly fierce market competition, how to improve product design efficiency and adapt to the rapid and ever-changing market demand has become a matter of great concern to enterprises. For this reason, computer-aided design has become an indispensable tool in design. With the improvement of CAD systems based on geometric models, people's requirements for computer-aided design systems are getting higher and higher, so the concept of product models is proposed, and it is hoped that it can provide comprehensive support for the entire design process. In fact, due to the complexity and variability of the actual situation, the product model basically remains on the basis of theoretical discussion. The actual demand and theoretical lag have led people to find another way. Therefore, designing a dedicated CAD system that can achieve a product assembly model to a certain extent, has begun to become a natural choice for many companies with specific design processes. This article shows how to use the object-oriented approach as a tool to achieve this goal by designing a dedicated CAD system for a product model.

1 Design example - air conditioning cabinet CAD system

Air conditioning cabinets are an integral part of large central air conditioners. It is mainly composed of a fan chamber, a coil chamber, a mixing chamber, etc., and provides a complete set of heat exchange facilities for the air conditioner. The outside air is extracted through the fan chamber, mixed in the mixing chamber, and then exchanged with the air conditioner in the coil chamber. Large air conditioners are different from household air conditioners. They are not mass-produced products, and are often single-piece products. Generally, air conditioner cabinet manufacturers design and customize according to different needs of users. Due to different installation forms and installation locations, different design parameters (such as power requirements), a specific design process is formed in which the product graphics are basically similar, but the local small structures are different, the sizes are different, and the specifications are complex and diverse. For each user, the company must design multiple sets of new drawings, which is time-consuming and labor-intensive, so that the design ability often cannot keep up with the actual production capacity and cannot meet the user's needs. To this end, manufacturers hope to have a dedicated product model-based CAD system that achieves the following functions:

. Automatically generate the original assembly drawing according to the user's needs;

. Ability to interactively modify parts as basic elements on the assembly drawing, and automatically maintain consistency of assembly relationships and consistency of 3D views;

. It can automatically generate machining information, such as process card, NC code, etc. according to the modified assembly drawing.

2 The choice of object-oriented method

Object-oriented methods are built on the basis that everything can be represented by objects. In system analysis and design, objects combine data and data manipulation behavior as an integrated whole. Modifications to the system only require changes, additions and deletions, and the basic object structure does not change. The object in the object-oriented analysis method is the direct mapping of the objective world object. The system using the object-oriented method for analysis and design is easier to understand than the system designed by the process-oriented analysis method, which enhances the maintainability of the system.

The advantages of the object-oriented approach make it adaptable to the needs of modern software engineering, and it is well suited to the design of product assembly models. Objects are abstractions of computer language to objective things; basic relationships between objects, such as association, dependence, tolerance, and inheritance, are abstractions of complex relationships between objective things. In the process design of the product model, mapping mechanical components directly to objects and mapping the assembly relationships between them to the association between objects is a very intuitive representation. In the system design, you can focus more on how to use the computer language to accurately describe the real world, rather than processing the data, making the whole design process more natural.

According to our actual situation, we decided to carry out secondary development on the parameter-based 2D CAD system and adopt object-oriented method for modeling.

At present, the more popular object-oriented design methods in China are OMT, BOOCH, etc. This design uses UML-based ROSE modeling tools. Various modeling ideas have their own focuses, but their basic ideas are consistent. What is important here is not what kind of object-oriented modeling method is used, but how to describe the objective world in a computer.

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