Statistical Process Control for True Position Measurements

Many manufacturers utilize statistical methods to control product characteristics during processing. Often traditional x charts are utilized. This method is appropriate when examining characteristics with one degree of freedom. For features with two or more degrees of freedom, traditional x charts may be misleading. Techniques for controlling characteristics with multiple degrees of freedom, however, have not been developed.

The purpose of this paper is to present a method of statistical analysis using radial type charting techniques for characteristics with multiple degrees of freedom. Included in this paper is a detailed discussion of the steps to prepare and interpret radial type charts. These techniques are applied to true position measurements as a specific example.