The Composition Principle of the Datum Reference Frame

The datum reference frame (DRF) is an orthogonal coordinate system used to locate the geometric features in tolerance technology and is a fundamental tool for tolerance analysis, tolerance validation and tolerance inspection. Additionally, establishment of the composition principle for DRF is an essential process for automation of tolerance technology. This paper presents the concept of a construction element of the DRF and the composition principle of DRF using the construction element. In this approach, the DRF is decomposed into three construction elements, i.e., a point, a line passing through the point, and a plane containing the line, and DRF is established by determining these three construction elements. The rules and algorithms used to determine the construction elements are established and the construction elements can be automatically established from the datum feature according to the rules and algorithm. The composition rules of the DRF are defined with the construction elements, and the DRF can be constructed automatically. The notion of and the establishment method for the construction elements can be used to validate the datum validity and the completeness of the datum system.