ISO 5459:2011 幾何学的製品仕様（GPS）—幾何学的公差—データムおよびデータムシステム | ページ 6

3.1

situation feature

point, straight line, plane or helix from which the location and orientation of features, or both, can be defined

3.2

datum feature

real (non-ideal) integral feature used for establishing a datum

Note 1 to entry: A datum feature can be a complete surface, a portion of a complete surface, or a feature of size.

Note 2 to entry: An illustration showing the relations between datum feature, associated feature and datum is given in Figure 4.

3.3

associated feature

associated feature for establishing a datum

ideal feature which is fitted to the datum feature with a specific association criterion

Note 1 to entry: The type of the associated feature is by default the same as the type of the nominal integral feature used to establish the datum (for an exception see 7.4.2.5).

Note 2 to entry: The associated feature for establishing a datum simulates the contact between the real surface of the workpiece and other components.

Note 3 to entry: An illustration showing the relations between datum feature, associated feature and datum is given in Figure 4.

3.4

datum

one or more situation features of one or more features associated with one or more real integral features selected to define the location or orientation, or both, of a tolerance zone or an ideal feature representing for instance a virtual condition

Note 1 to entry: A datum is a theoretically exact reference; it is defined by a plane, a straight line or a point, or a combination thereof.

Note 2 to entry: The concept of datums is inherently reliant upon the invariance class concept (see Annex A and Annex B).

Note 3 to entry: Datums with maximum material condition (MMC) or least material condition (LMC) are not covered in this International Standard (see ISO 2692).

Note 4 to entry: When a datum is established, for example, on a complex surface, the datum consists of a plane, a straight line or a point, or a combination thereof. The modifier [SL], [PL] or [PT], or a combination thereof, can be attached to the datum letter to limit the situation feature(s) taken into account relative to the surface.

Note 5 to entry: An illustration showing the relation between datum feature, associated feature and datum is given in Figure 4.

3.5

primary datum

datum that is not influenced by constraints from other datums

3.6

secondary datum

datum, in a datum system, that is influenced by an orientation constraint from the primary datum in the datum system

3.7

tertiary datum

datum, in a datum system, that is influenced by constraints from the primary datum and the secondary datum in the datum system

3.8

single datum

datum established from one datum feature taken from a single surface or from one feature of size

Note 1 to entry: The invariance class of a single surface can be complex, prismatic, helical, cylindrical, revolute, planar or spherical. A set of situation features defining the datum (see Table B.1) corresponds to each type of single surface.

3.9

common datum

datum established from two or more datum features considered simultaneously

Note 1 to entry: To define a common datum, it is necessary to consider the collection surface created by the considered datum features. The invariance class of a collection surface can be complex, prismatic, helical, cylindrical, revolute, planar or spherical (see Table B.1).

3.10

datum system

set of two or more situation features established in a specific order from two or more datum features

Note 1 to entry: To define a datum system, it is necessary to consider the collection surface created by the considered datum features. The invariance class of a collection surface can be complex, prismatic, helical, cylindrical, revolute, planar or spherical (see Table B.1).

3.11

datum target

portion of a datum feature which can nominally be a point, a line segment or an area

Note 1 to entry: Where the datum target is a point, a line or an area, it is indicated as a datum target point, a datum target line or a datum target area, respectively.

3.12

moveable datum target

datum target with a controlled motion

3.13

collection surface

two or more surfaces considered simultaneously as a single surface

Note 1 to entry: Table B.1 is used to determine the invariance class of a datum or datum systems when using a collection of surfaces.

Note 2 to entry: Two intersecting planes may be considered together or separately. When the two intersecting planes are considered simultaneously as a single surface, that surface is a collection surface.

3.14

feature of size

geometrical shape defined by a linear or angular dimension which is a size

Note 1 to entry: The features of size can be a cylinder, a sphere, two parallel opposite surfaces, a cone or a wedge.

[SOURCE:ISO 14660-1:1999, 2.2]

Note 2 to entry: In this International Standard, features which are not features of size according to ISO 14660-1 are used to establish a datum as a feature of size, e.g. a truncated sphere (see the example in C.1.4).

3.15

objective function

objective function for association

formula that describes the quality of association

Note 1 to entry: In this International Standard, the term “objective function” refers to “objective function for association”.

Note 2 to entry: The objective functions are usually named and mathematically described: maximum inscribed, minimum zone, etc.

3.16

association

operation used to fit ideal feature(s) to non-ideal feature(s) according to an association criterion

[SOURCE:ISO 17450-1:—, 3.2]

3.17

constraint

limitation on the associated feature

3.18

association criterion

objective function with or without constraints, defined for an association

Note 1 to entry: Several constraints may be defined for an association.

Note 2 to entry: Association results (associated features) may differ, depending upon the choice of association criterion.

Note 3 to entry: Default association criteria are defined in Annex A.

3.19

integral feature

surface or line on a surface

Note 1 to entry: An integral feature is intrinsically defined.

[SOURCE:ISO 14660-1:1999, 2.1.1]

3.20

contacting feature

ideal feature of any type which is different from the nominal feature under consideration and is associated with the corresponding datum feature

Figure 1 — Example of a contacting feature

a)Contacting feature on nominal model

b)Contacting feature on real workpiece

Key

1	contacting feature: ideal sphere in contact with the datum feature or the feature under consideration
2	features under consideration: nominal trapezoidal slot (collection of two non-parallel surfaces)
3	datum feature: real feature corresponding to the trapezoidal slot (collection of two non-parallel surfaces)

3.21

invariance class

group of ideal features for which the nominal surface is invariant for the same degrees of freedom

Note 1 to entry: There are seven invariance classes (see Annex B).

3.22

theoretically exact dimension

TED

dimension indicated on technical product documentation, which is not affected by an individual or general tolerance

Note 1 to entry: For the purpose of this International Standard, the term “theoretically exact dimension” has been abbreviated TED.

Note 2 to entry: A theoretically exact dimension is a dimension used in an operation (e.g. association, partition, collection, …).

Note 3 to entry: A theoretically exact dimension can be a linear dimension or an angular dimension.

Note 5 to entry: A TED is indicated by a value in a rectangular frame.

[SOURCE:ISO 1101:2004/Amd 1:—, 3.7]