Machine tool fixture parametric parts graphics library and system

In the development of a Computer-Aided Fixture Design System (CAFD), the graphical library for machine tool fixtures plays a crucial role. Traditionally, these libraries are embedded within CAD software, which limits their scalability for systems with a large number of components. Modern fixture systems, however, include thousands of part types and specifications, especially those following standards like GB. Additionally, combinations such as slotted and hole-assembly fixtures, along with pneumatic and hydraulic components, further increase the complexity. Therefore, the CAFD system requires a standalone graphics library that can be accessed and retrieved independently. Parametric technology offers advantages such as simplified storage, easier modifications, and reduced space usage. To meet these needs, we have developed a client/server-based parametric graphics library for machine tool fixtures.

1. Design Plan

1) Client/Server Architecture

With the increasing use of networks for resource sharing, object-oriented methods and client/server architectures have become popular. In this architecture, multiple computers are connected in a network. The machines handling application processing are called clients, while those managing database services are referred to as servers. Communication between them is facilitated through middleware. Clients handle user interfaces, data input, application processing, and database requests, while servers manage database queries, result formatting, integrity checks, and access control.

2) Hardware and Software Solutions

The parametric graphics library system uses a client/server model. The hardware setup includes an IBM PC server and several client machines with PII450 processors, 64MB RAM, and 10.4GB HDD. The software environment runs on Windows NT 4.0 for both server and client, using TCP/IP as the network protocol and Microsoft SQL Server 6.5 as the database. The client application was developed using Visual C++ 6.0 and AutoCAD R14.

3) Overall Framework of Parametric Graphics Library

In this system, the parameters of machine tool components are stored on the server. Using C++, we generate parametric graphics for fixtures by reading values from the database. Users can interactively modify field values, which are then passed as size parameters to the drawing functions in AutoCAD, enabling parametric design. The overall design is illustrated in Figure 1.

Figure 1: Overall Design Plan

2. Database Design

Database Structure Design

Each part of the machine fixture has its own table in the SQL Server database. Due to dimensional dependencies among parameters, incorrect inputs can lead to drawing errors. To prevent this, validity rules are implemented. If a user input does not conform to the dimensional chain, an error message is displayed, allowing for basic error correction in the interface.

Database Operation Interface Design

Microsoft Visual C++ 6.0 provides powerful tools for database programming, making it easy to implement query, add, delete, and modify functions for data records.

3. C++ Interface Program for Database in Parametric Drawing

AutoCAD introduced the ASI (AutoCAD SQL Interface) in its 12th edition, allowing SQL language integration for external database access. However, ASI required drivers and had limited flexibility, making development time-consuming. ObjectARX, on the other hand, offers a more efficient and stable solution. Based on C++, it provides direct access to the AutoCAD database and supports MFC for rich UI development. Compared to ADS and AutoLISP, ARX applications are faster and more reliable.

I used ObjectARX written in Visual C++ 6.0 to connect to the database. For example, the A-type flat plate used in clamps demonstrates how to operate the database in parametric drawing. ODBC (Open Database Connectivity) was used to connect to the server’s fixture database. It allows applications to access different databases without changes, ensuring compatibility and reducing development effort.

By creating recordset classes and dialog boxes, users can navigate through database records, edit parameter values, and validate them against dimensional constraints. If valid, the values are passed to the drawing function; otherwise, an error is shown.

4. Conclusion

The parametric graphics library based on a client/server model offers large capacity, reliability, and stability. It allows various CAFD systems to be installed on clients, supporting multi-user design in a networked environment. The system meets CAFD requirements for parts libraries and can be adapted for other mechanical design applications. Its structure holds significant universal value for computer-aided design systems across industries.

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