Computer aided design (CAD) system for automatically constructing datum reference frame (DRF) and feature control frame (FCF) for machine part

摘要

A formal drawing for a machine part includes datum features that are used to construct a Datum Reference Frame (DRF) for the part. A Feature Control Frame (FCF) for each datum feature that is intended to eliminate roll about a fixed primary axis of the DRF includes a material location modifier which specifies whether the orientation or the location of the feature should be used to eliminate roll. The material location modifiers enable specification of Independent of Material Location (IML), at Basic Material Location (BML), at Maximum Material Location (MML) and at Least Material Location (LML), eliminate all ambiguity in the formal drawing, and enable a DRF to be constructed automatically using a computer. The material location modifiers further eliminate any possibility of misinterpretation of the formal drawing during all stages of manufacture and inspection of the part. A computer program implementing a method of the invention includes instructions for constructing a DRF in response to the dimensions, tolerances, FRC datum feature sequence and material location modifiers using a set of rules and specific DRF construction tools. The tools include ORIENT, ALIGN, PIVOT, SET ORIGIN, TRANSLATE and ROTATE, and are applied in order to sequentially eliminate pitch, yaw, roll, and translation from the DRF.