Abstract: A series of principles about fixture locating plan are proposed to automate the selection of locating datum and the layout of locating points. The constraint degrees of freedom (DOF) of workpiece datum can be classified into four types: linear translation DOF, linear rotation DOF, planar translation DOF and planar rotation DOF. The acquirement of constraint DOFs is realized by automatically extracting process requirements. Four kinds of constraint DOFs are represented in the format of vectors, and the locating capability of workpiece datum is denoted by the layout of locating points, by which the operation rules of constraint DOFs, such as merge rule, decomposition rule and coordinate transformation rule, are established. The evaluation method of datum locating ability and the judging method of datum conflicts are studied. The approach to the resolution of the datum conflicts and the datum locating problem is presented, and the rule of the layout of locating points is established.

Key words: Constraint degree of freedom, Fixture locating plan, Locating ability, Workpiece locating datum