Geometrical Product Specification
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Geometrical Product Specification Vijay Srinivasan* Systems Integration Division, Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, USA
Synonyms Dimensional tolerancing and metrology; Geometrical dimensioning and tolerancing; Product manufacturing information
Definition There are two definitions for the phrase “geometrical product specifications” (GPS). In a narrower sense, it refers to geometrical dimensioning and tolerancing (GD&T) and surface texture for specifying allowable geometric variations in a manufactured product. The International Organization for Standardization (ISO) has adopted a broader definition of GPS that includes specifications as well as verification (using measurements) of allowable geometric variations in a product. This entry adopts the broader ISO definition. In this context, the acronym GPS should not be confused with its more popular usage as the “global positioning system.”
Theory and Applications Introduction
The phrase “geometrical product specifications” was formally introduced in 1996, when a new ISO Technical Committee 213 (ISO/TC 213) titled “Dimensional and geometrical product specifications and verification” was formed. The committee’s scope is the “standardization in the field of geometrical product specifications (GPS), i.e., macro- and microgeometry specifications covering dimensional and geometrical tolerancing, surface properties and the related verification principles, measuring equipment and calibration requirements including the uncertainty of dimensional and geometrical measurement. The standardization includes the basic layout and explanation of drawing indications (symbols).” All the standards produced by this technical committee start with the label “Geometrical Product Specifications (GPS),” thereby establishing GPS as a brand for this committee’s ISO standards. GPS standards follow a set of well-founded axioms and principles. Two of the basic GPS axioms are: A1. Axiom of manufacturing imprecision: All manufacturing processes are inherently imprecise and produce parts that vary. In fact, no manufactured object can have ideal form. A2. Axiom of measurement uncertainty: No measurement can be absolutely accurate, and with every measurement, there is some finite uncertainty about the value of the measurand (particular quantity subject to measurement).
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CIRP Encyclopedia of Production Engineering DOI 10.1007/978-3-642-35950-7_16757-1 # CIRP 2015
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Fig. 1 A simple illustration of the GPS language. (a) Syntax of GPS flatness tolerance specification. (b) Semantics of GPS flatness tolerance specification
In addition, these standards have adopted recent mathematical and computational advances in areas such as the classification of continuous symmetry groups (Srinivasan 2004; Nielsen 2012) and computational coordinate metrology (Srinivasan 2007).
GPS Language GPS standards define a GPS language, whose syntax consists of a well-structured set of symbols and numbers. The semantics (geometric meani
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