Management Data
Management data is used by design, manufacturing process planning, manufacturing execution, and by quality organizations, all as a common layer for authority and identification. The management data requirements of ASME Y14.41-2012 and ISO 16792 are supported by the existing STEP product data management (PDM) information model and by a new module ISO/TS 10303-1810 Product and manufacturing information view context. As an example, the tolerance principle to apply to a model is basic information needed by manufacturing process planning, fabrication and inspection. However, the tolerance principle specified by ASME is different than the tolerance principle specified by ISO. The tolerance principle is applied to a model by a formal specification of the dimensioning standard that shall be used to interpret the model GPS data. The integration of the existing PDM information model and ISO/TS 10303-1810 into ISO 10303-242 resulted in the ability to specify the dimensioning standard that applies. The ISO/TS 10303-1811 Product and manufacturing information with nominal 3D model module supports the ability to declare that the model geometry is nominal as defined in ISO 17450-1.
The ISO/TS 10303-1050 Dimension tolerance, ISO/TS 10303-1051 Geometric tolerance, and ISO/TS 10303-1816 Model based 3d geometrical dimensioning and tolerancing representation modules provide manufacturing technology independent GPS information for use by design, manufacturing process planning, manufacturing execution, and by inspection, all as a common layer for geometric functionality. Improvements in product feature identification capability to support quality failure reporting have been provided by updates to ISO/TS 10303-1032 Shape property assignment{#57427}. Improvements in geometric model element identification capability to support GPS requirements have been provided by updates to ISO 10303-41{#59269}.
The ISO/TS 10303-1812 Product and manufacturing annotation presentation module supports annotation of nominal 3D geometric models with text and graphics that can be used by design, manufacturing process planning, and inspection human processes.
Presentation and representation
The state of the practice that existed in the initial STEP mechanical design domain AP development was that during one activity a user interacts with a CAD system to build a geometric model based on ISO 10303-42{#23019}; during a separate activity a user interacts with a CAD system to annotate that geometric model with graphic information based on ISO 10303-46{#30634}; during a separate activity a user interacts with a CAD system to annotate that geometric model with semantic dimensioning and tolerancing information based on ISO 10303-47:1997. The separate activities lead to editions one of AP 203, AP 202{#36506}, and AP 224 respectively. The result is that there a recognition gap{#94591} between the annotation and the dimensioning data sets of models created based on those editions. The recognition gap persists in ISO 10303-242. There is a conceptualization gap between requirements and notes{#94591} in the ISO 10303 mechanical domain information models. The conceptualization gap persists in ISO 10303-242 increasing interoperability costs between e.g., system engineering and mechanical engineering communities.
Persistent identification
Persistent identification{#63300} support has been improved with the introduction of unique constraints on key GPS related entity types: shape_aspect, shape_aspect_relationship, dimensional_size, dimensional_location and geometric_tolerance in the context of a single product_definition_shape. When combined with the unique constraint on geometric_item_specific_usage, a requirement for being able to persistently associate a geometric entity (e.g., advanced_face) with a tolerance has been satisfied for the case of a specific combination of product_definition_shape and representation in the exchange model.
Feature classification
As noted earlier, model feature classification is supported to some extent in ISO 10303-242. The classification of a model feature is derived from the user actions during the process of adding GPS information to the design model.
The updated ASME and ISO standards require that the designer provide a feature based geometric model and define a specific class of feature, a model feature. However, the concept of feature is not a fundamental geometric construct (e.g., point, line, face) in CAD geometry and the user must interact with the CAD system to instantiate each model feature class and specify one or more associated geometric elements for that model feature instance. STEP provides the generic shape_aspect ENTITY type to represent a feature and ISO 10303-47 provides the ability to classify a feature as a model feature. The number of model feature classes included in ISO 10303-242 is a significant improvement over earlier APs and contributes toward meeting the “tolerance feature” requirement noted in {#90745}.
Symmetry groups, invariant classes
Some of the ASME and ISO specification operators assume the existence of a specific group of geometric properties (e.g., continuity among certain model element boundaries) of the model feature. The names of those ASME and ISO specification operators are used as names of subtypes of shape_aspect (e.g., continuous_shape_aspect) in an initial design feature classification scheme included in the second edition of ISO 10303-47.
The ISO standards include the further classification of model features of revolute class, a mathematical property of the underlying geometric model of the feature instance. Some of the ISO tolerance classes require that model features belong to one of the following invariance classes defined in ISO/TS 17450-1{#26865}: Complex, Prismatic, Revolute, Helical, Cylindrical, Planar and Spherical. When a feature instance is assigned to a tolerance that is only permitted to be assigned to a specific revolute class the CAD system will be required to assert that the feature instance is also a member of that revolute class. An example is the roundness_tolerance ENTITY type included in ISO 10303-47. A roundness_tolerance is a subtype of geometric_tolerance. A roundness_tolerance may only be assigned to a feature instance whose underlying geometry is a surface revolute but is not a helical shape. The available geometric model ENTITY types in the ISO 10303-514 Advanced boundary representation schema include some ENTITY types that map directly to a revolute class (e.g., plane, cylindrical_surface) but in the majority of cases the authoring CAD system will be responsible for ensuring that the model feature underlying geometry meets the requirements of the invoked invariance class.
Datum system
[[This needs rework to remove redundancy.]]
The ASME standards refer to the combination of the last compartments in a tolerance frame that references datum features as a datum reference system. The ISO standards refer to that combination as a datum system if there are two or more compartment and as a single datum if there is only one compartment. An explicitly modeled datum system is implied in the current edition of ISO 16792 and ASME Y14.41-2012 because they require a model coordinate system associated to a datum system and the STEP information model architecture requires the existence of an instance of product data (e.g., a shape_aspect) against which to assign a coordinate system. The new ENTITY type datum_system supports both the ASME and ISO definitions by supporting references of from one to three datum_reference_compartments in a given order, where a datum_reference_compartment represents a compartment in a tolerance frame. The datum_system ENTITY type is a subtype of shape_aspect, providing the capability to assign properties to the datum_system for future extensions.[1] In particular, a datum_system might have an associated model coordinate system.[2]
ISO 5459 provides requirements for the datum system to be composed of datums or modified datums either singly or in a tree structure{Cormen et al., 1990, #99880}. The root is a datum_reference_compartment. All intermediate nodes are datum_reference_element and the leaf entity types are datum. The common_datum_list satisfies the common datum requirement by providing a list of 1 to many datum_reference_elements. This structure allows us to model complex common data structures (e.g., "( A - B ) xxx - ( C - D) yyy”).
The new ENTITY type datum_system references one to three datum_reference_compartments in a given order. A datum_reference_compartment represents a compartment in a datum feature control frame. The ASME standards refer to the combination of the last compartments in a tolerance frame that references datum features as a Datum Reference System. The ISO standards refer to that combination as a Datum System if there are two or more compartment and as a Single Datum if there is only one compartment. The new entity datum_system supports both the ASME and ISO definitions. Datum_system is a subtype of shape_aspect, providing the capability to assign properties to the datum_system for future extensions. In particular, a datum_system might have an associated model_coordinate_system.
ISO 5459 provides requirements for the datum system to be composed of datums or modified datums either singly or in a tree structure.[3] The root is a datum_reference_compartment. All intermediate nodes are datum_reference_element and the leaf entity types are datum. The common_datum_list satisfies the common datum requirement by providing a list of 1 to many datum_reference_elements. This structure allows us to model complex common data structures (e.g., "( A - B ) xxx - ( C - D) yyy”). The recursion provides the ability to nest items (e.g., “( ( A - B ) xxx - ( C - D )) yyy”).
Figure 8. A tree structure is formed by the recursive path from datum_reference_compartment to base to datum_reference_element that must terminate on datum in the role of base.