Propuesta de análisis de las situaciones propuestas

3.2.1 The relationships between the system and other CAx systems The geometrical tolerances and surface texture play important roles during assembly, friction, wear and lubrication of parts. Thereby, design of geometrical tolerances is an important link after the structural design of a product. Computer aided tolerancing can help designer to make decisions in this process at a certain extent. CAPP bridges the design and manufacture, and it assigns geometrical tolerances to various processing steps in manufacturing process. The wide use of digital measurement equipment such as CMM (Coordinate Measuring Machine) was a revolution for measurement technique. Two important effects came out.

Firstly, the consequent data processing with digital measurement technique is different with conventional one; this will force the assessment to change.

Secondly, the software used in the digital measurement technique pushes forward the digitization of manufacturing industry. Then, the communication and exchange of data among different systems becomes another problem.

With the development of STEP, there is no need for direct communication and exchange of data among different systems such as CAD, CAPP and the integrated geometry information system. And this can be accomplished by

STEP-XML for product data representation and exchange.

In this thesis, CAD is used as the host system. And the popular CAD systems have interface for further development, such as ObjectARX for AutoCAD, UG/Open API for Unigraphics, and so on. The output of The Integrated Geometry Information System, which is the XML format, will be transformed to the inner format that the CAD system supports. The integrated framework of the integrated geometry information with other CAx software is presented in Figure 3.1.

Figure 3.1 Framework of the integration between the integrated geometry information system with other CAx systems

3.2.2 The Framework of the System

In order to reduce the uncertainty during design and metrology process, thus to reduce specification uncertainty, method uncertainty and implementation uncertainty, GPS standard system aims to strengthen the completeness of geometrical specifications, i.e. to consider the function, type of geometrical specification, type of geometrical feature, geometrical requirement, and various operations and the nesting indexes to obtain the geometrical feature, evaluation parameter and so on.

It should be addressed that:

(1) The comprehensive consideration of information related to geometrical product specifications above, it makes the geometrical product specifications more complete and unambiguous. However, if all this information is presented in one drawing indication, it will cause ‘traffic jam’, further to reduce the readability of the drawing indication.

(2) Some components such as geometrical requirements, filtration and association algorithms, are easily to be determined in the process of design.

the drawing indication. For example, if particular inspection method is prescribed, this would force the manufacturer to provide inspection devices prescribed by the customer, although other sufficient inspection devices are already available, this will cause unnecessary cost.

(3) One particular method that differs in assessment from the precise tolerance zone requires further specifications of the measuring conditions. Especially for the precise tolerance zone, further specifications of the measuring conditions should be specified.

(4) The determination of the component involved in geometrical specifications should be user-machine interactive, and it can not be finished automatically.

CAD/CAM/CAPP/CMM-systems are the necessary tools for the implementation of Concurrent Engineering (CE). The integrated information system for GPS integrates the information of geometrical tolerancing, involving function, design, manufacture and verification, and it is an important component of CE. GPS standard system utilizes the enriched GPS language to express the GPS specifications complete, unique and unambiguous to meet the different functions of geometrical product. And, it makes the measured value of geometrical specifications and specified value to be comparable, thus to reduce the specification uncertainty, method uncertainty and implementation uncertainty.

Figure 3.2 shows the relationship between function, design, manufacture and verification of geometrical products.

Figure 3.2 Relationships among function, design, manufacture and verification of a product [105]

The integrated geometry information system consists of three core modules:

Database module, Knowledge base module and Host module. The Database module is the fundamental part of the system, and the knowledge base

subsystem is the key part for the intellectualization of the system. The entities in various phases of the product and their relationships are modelled in the database module. The running of the whole system relies on it. The Knowledge base module operates on the database module. It uses the knowledge rules stored in it to help the designer make decisions. The issues that should be solved in each part are the establishment of the computer representing model of the entities, their relationships and the establishment of the knowledge rules in different phases of product. One of the most common applications of the system is to combine it with CAD to visualize the geometrical specification of drawings.

Consequently, the host module is another important part of the system. This project mainly combines the system with CAD software. The framework of the system is presented in Figure 3.3.

Figure 3.3 Framework of the Integrated Information System