The Tools & Rules for Computer Automated Datum Reference Frame Construction

Abstract

This paper describes a complete and unambiguous method for defining andconstructing Cartesian coordinate systems in machine components, enabling automation of this activity in Computer Aided Design (CAD), Computer Aided Manufacturing and Computer Aided Metrology applications. Basedon theASME Y14.5M 1994 conventions of Datum Feature labels and Feature Control Frames, the method uses definitive mathematical tools and rules, fully described herein, to (1) eliminate all known ambiguities, (2) expand the available alternatives and (3) make computer automation of the Datum Reference Frame construction process possible. The tools described herein consist of the mathematical operations: ORIENT, ALIGN, PIVOT, SET ORIGIN, TRANSLATE and ROTATE, well known in coordinate metrology. The rules described herein are identified by the names:

• 1. Datum Feature Precedence

• 2. Degrees of Freedom Precedence

• 3. Non-Override

• 4. Maximum Utilization

• 5. Datum Feature Simulator Form Control

• 6. Datum Feature Simulator Orientation Control

• 7. Datum Feature Simulator Size Control

• 8. Datum Feature Simulator Location Control

• 9. Compound Datum Feature Simulation

• 10. Composite Feature Control Frames

• 11. Degrees of Freedom Modification

• 12. Simultaneity

Some rules are merely precise formulations of existing or implied rules in the Y14J standard, others are entirely new. In addition to derivations of the rules anddescriptions of the tools, the paper includes (1) an example of automatic DRF construction, (2) an example of how the method eliminates current ambiguities in the definition of “natural” Datum Reference Frames, and (3) an example of how the method permits specifying “artificiar” Datum Refer- enceFrames. Note: A patent has been applied for by the author covering certain portions of the methods described.