Geometrical Product Specification and Verification (GPS&V) is a set of ISO standards developed by ISO Technical Committee 213. The aim of those standards is to develop a common language to specify macro geometry (size, form, orientation, location) and micro-geometry (surface texture) of products or parts of products so that the language can be used consistently worldwide.
Background GPS&V standards cover:
Dimensional specifications Macrogeometrical specifications (form, orientation, location and run-out) Surface texture specifications Measuring equipment and calibration requirements Uncertainty management for measurement and specification acceptance Other ISO technical committees are strongly related to ISO TC 213. ISO Technical Committee 10 is in charge of the standardization and coordination of technical product documentation (TPD). The GPS&V standards describe the rules to define geometrical specifications which are further included in the technical product documentation. The technical product documentation is defined as the:
The technical product documentation can be either a conventional documentation made of two dimensional engineering drawings or a documentation based on computer-aided design (CAD) models with 3RD annotations. The ISO rules to write the documentation are mainly described in ISO 128 and ISO 129 series while the rules for 3RD annotations are described in ISO 16792. ISO Technical Committee 184 develops standards that are closely related to GPS&V standards. In particular ISO TC 184/SC4 develops ISO 10303 standard known as STEP standard (see STEP-file). GPS&V shall not to be confused with the use of ASME Y.14.5 which is often referred to as geometric dimensioning and tolerancing (GD&T).
History and concepts
History ISO TC 213 was born in 1996 by merging three previous committees:
ISO Technical Committee 10 Sub-committee 5 (ISO/TC 10/SC5) Geometrical Tolerancing ISO Technical Committee 57 (ISO/TC 57) Surface Texture ISO Technical Committee 3 (ISO/TC 3) Limits and fits
Operation GPS&V standards are built on several basic operations defined in ISO 17450-1:2011:
Skin model Partition Extraction Filtration Association Collection Construction Reconstruction Reduction Those operations are supposed to completely describe the process of tolerancing from the point of view of the design and from the point of view of the measurement. They are presented in ISO 17450 standard series. Some of them are further described in other standards e.g ISO 16610 series for filtration. Those concepts are based on academic works. The key idea is to start from the real part with its imperfect geometry (skin model) and then to apply a sequence of well defined operations to completely describe the tolerancing process. The operations are used in the GPS&V standards to define the meaning of dimensional, geometrical or surface texture specifications.
Skin model The skin model is a representation of the surface of the real part. The model in CAD systems describes the nominal geometry of the parts of a product. The nominal geometry is perfect. However, the geometrical tolerancing has to take into account the geometrical deviations that arise inevitably from the manufacturing process in order to limit them to what is considered as acceptable by the designer for the part and the complete product to be functional. This is why a representation of the real part with geometrical deviations (skin model) is introduced as the starting point in the tolerancing process.
Partition The skin model is a representation of a whole real part. However, the designer very often, if not always, needs to identify some specific geometrical features of the part to apply well-suited specifications. The process of identifying geometrical features from the skin model or the nominal model is called a partition. The standardization of this operation is a work in progress in ISO TC 213 (ISO 18183 series). Several methods can be used to obtain a partition from a skin model as described in
Extraction The skin model and the partitioned geometrical features are usually considered as continuous, however it is often necessary when measuring the part to consider only points extracted from a line or a surface. The process of e.g. selecting the number of points, their distribution over the real geometrical feature and the way to obtain them is part of the extraction operation. This operation is described in ISO 14406:2011
Filtration Filtration is an operation that is useful to select features of interest from other features in the data. This operation is heavily used for surface texture specifications however, it is a general operation that can be applied to define other specifications. This operation is well known in signal processing where it can be used for example to isolate some specific wave length in a raw signal. The filtration is standardized in ISO 16610 series where a lot of different filters are described.
Association Association is useful when we need to fit an ideal (perfect) geometrical feature to a real geometrical feature e.g. to find a perfect cylinder that approximates a cloud of points that have been extracted from a real (imperfect) cylindrical geometrical feature. This can be viewed as a mathematical optimization process. A criterion for optimization has to be defined. This criterion can be the minimisation of a quantity such as the squares of the distances from the points to the ideal surface for example. Constraints can also be added such as a condition for the ideal geometrical feature to lie outside the material of the part or to have a specific orientation or location from an other geometrical feature. Different criteria and constraints are used as defaults throughout the GPS&V standards for different purposes such as geometrical specification on geometrical features or datum establishment for example. However, standardization of association as a whole is a work in progress in ISO TC 213.
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