Limitations of notation system in centred part alignment accuracy imposed by ISO standard and proposal for an improved methodology

According to the ISO Geometrical Product Specifications (GPS), centred part alignment with one centred point can be described clearly using technical drawings. There are two main limitations of this standard; Firstly: the uncertainty over use of notations in technical drawings when more than one centred point is applied, and secondly, the use of fixed datum targets to centred points which causes an unstable alignment process. This article suggests a new approach for a functional, explicitly defined notation system of datums and datum systems based on the research of orientation constraints between datums. This new approach simplifies the technical drawing, thereby eliminating notation uncertainties. An improved methodology for a stable alignment process was developed based on physical analysis of the centred part alignment which implements movable datum targets.