PDM-UG: Quantified Component Usage
From WikiSTEP
This page belongs to the PDM Usage Guide.
The basic explicit assembly represents a single occurrence of the component definition within the assembly definition. Multiple occurrences of a constituent used in an assembly are represented in two ways in the PDM Schema:
- quantified usage occurrence,
- multiple individual usage occurrences.
The quantified usage occurrence associates a quantity with the component usage, but does not allow independent identification of individual occurrences when a component definition is used multiple times.
The PDM Schema uses separate single usage occurrences to represent multiple occurrences of a component within an assembly when the various components must be distinguished individually (see Multiple Individual Component Occurrences).
The quantified usage occurrence associates a quantity value with the multiple use of a component definition in the parent assembly definition. The quantified usage occurrence simply relates a quantity value with the multiple component occurrences; it does not distinguish the individual occurrences independently. The quantified usage occurrence is most commonly used for standard component parts, such as fasteners, that need to be quantified but do not need to be individually distinguished. This structure corresponds to a basic indentured parts list with the associated part quantity values (see Figure 3).
Contents |
The Instance Model: EXPRESS entities and attributes
The EXPRESS entities and attributes used to support the requirements for quantified assembly structure are shown in Diagram 21.
Quantified assembly component usage
This entity is a subtype of assembly_component_usage. When the quantified_assembly_component_usage is required, it should be created as an AND instantiation with the next_assembly_usage_occurrence. It adds the attribute quantity to identify the number of occurrences of the constituent definition that are used in the parent assembly. With the quantified_assembly_component_usage, multiple individual occurrences of the constituent part are not distinguished independently.
Attributes
- The quantity attribute gives the number of usage occurrences of a component within an assembly.
| ENTITY quantified_assembly_component_usage | Attribute Population | Remarks |
| id | see supertype | |
| name | see supertype | |
| description | see supertype | OPTIONAL |
| relating_product_definition | see supertype | reference to assembly |
| related_product_definition | see supertype | reference to component |
| reference_designator | see supertype | OPTIONAL should not be instantiated |
| quantity | type : entity = measure_with_unit |
===Preprocessor Recommendations=== This entity should be instantiated when quantities greater than one need to be represented, but when the individual occurrences do not need to be independently distinguished. This is created as a "complex" instance of next_assembly_usage_occurrence AND quantified_assembly_component_usage. For a quantity of one, a simple instance of next_assembly_usage_occurrence alone may be used. However, quantified_assembly_component_usage needs to be used if the number of occurrences is specified by a specific unit, e.g., the usage of "one liter of oil" as a component in an assembly.
===Postprocessor Recommendations=== When importing an instance of next_assembly_usage_occurrence AND quantified_assembly_component_usage, a quantity value of one should be interpreted as equivalent to the simple next_assembly_usage_occurrence.
===Related Entities=== None specified.
The Instance Model: STEP exchange file format (ISO10303 Part 21 syntax)
/* primary application context and life cycle stage */
#10 = APPLICATION_CONTEXT('mechanical design');
#220 = PRODUCT_CONTEXT('', #10, '');
#230 = PRODUCT_DEFINITION_CONTEXT('part definition', #10, 'design');
/* type discriminator for part as product */
#100 = PRODUCT_RELATED_PRODUCT_CATEGORY('part', $, (#380, #440));
/* part master for component definition */
#360 = PRODUCT_RELATED_PRODUCT_CATEGORY('detail', $, (#380));
#380 = PRODUCT('g1', 'gasket', $, (#220));
#390 = PRODUCT_DEFINITION_FORMATION('A','',#380);
#400 = PRODUCT_DEFINITION('gv1', 'design view on gasket', #390, #230);
/* part master for assembly definition */
#420 = PRODUCT_RELATED_PRODUCT_CATEGORY('assembly', $,(#440));
#440 = PRODUCT('s1', 'sleeve assembly', $, (#220));
#450 = PRODUCT_DEFINITION_FORMATION('A','',#440);
#460 = PRODUCT_DEFINITION('sv1', 'design view on sleeve assembly', #450, #230);
/* quantified multiple use occurrence of component within assembly */
#860 = DIMENSIONAL_EXPONENTS(0.0E+000, 0.0E+000, 0.0E+000, 0.0E+000,
0.0E+000, 0.0E+000, 0.0E+000);
#870 = NAMED_UNIT(#860);
#880 = MEASURE_WITH_UNIT(COUNT_MEASURE(2), #870);
#890 = (ASSEMBLY_COMPONENT_USAGE($) NEXT_ASSEMBLY_USAGE_OCCURRENCE()
PRODUCT_DEFINITION_RELATIONSHIP('guQgum', 'quantified instance usage',
'quantified usage of gasket', #460, #400) PRODUCT_DEFINITION_USAGE()
QUANTIFIED_ASSEMBLY_COMPONENT_USAGE(#880));
Illustrated Example: Parts Lists and Item Find Number
The following example illustrates the mechanical drawing and corresponding parts list for two typical example assembly parts, PCA A and PCA B. Each drawing illustrates the use of the item find number.
Parts list for PCB A
| Find number | Part number | Description | Remarks | Quantity |
| 90 | con1001 | Connector | 1 | |
| 91 | scr2101 | Screw | 3 | |
| 92 | mem801 | Memory | U1,U2 | 2 |
| …… |
Parts list for PCB B
| Find number | Part number | Description | Remarks | Quantity |
| 13 | res225 | Resistor | 1 | |
| 14 | mem801 | Memory | U1 | 1 |
| …… |
Figure 4: Illustrated example of drawings, associated parts lists, and item find numbers
In the example above, the same component (part number mem801) is used in both assemblies PCB A and PCB B. However, the item find number is different for each assembly. The item find number assigns to the component a name that is specific to the assembly in which it is being used. In the PDM Schema, the item find number may be assigned to the name attribute of next_assembly_usage_occurrence.
ISO 6433-1981 has the concept called "item references". This concept is simply the callout of a component on an assembly drawing via a number which is identified by the same number in the parts list. The find number is a unique identifier when multiple uses relationships (such as to Quantified_Assembly_Component_Usage) are created. For example, when quantities vary by effectivity, a find number is required. The "Find Number" on the relationship "lists parts masters" between the parts lists document and the component.
The drawing find number is used to identify components in drawings. Similarly drawing find number assigns to the component a name that is specific to a drawing in which the component is being used. The mapping of drawing find number or item reference should be between the drawing or drawing parts list and the component. The concept of ‘drawing find number’ should not be mapped to next_assembly_usage_occurrence.name between the assembly and the component but should be used in the relationship between the component and the drawing of the assembly.
In the PDM Schema the item find number may be assigned to the name attribute of next_assembly_usage_occurrence. The same attribute should be used if the part occurrence is instantiated as quantified_assembly_component_usage.
