Using Assembly Relations to Control Both Assembly and Component Dimensions in Pro/ENGINEER Wildfire 3.0

Assembly relations can be used to control geometry at the assembly level, the sub-assembly component level and the part level. Assembly relations function in a similar way to part relations. In an assembly relation, the component which contains the dimension to be controlled by the assembly relation must be specified. Controlling part geometry at the assembly level allows assembly design intent to propagate down through the components of the assembly.

The assembly desk_lamp.asm shown in Figure 1 will be used in this example.

• The assembly was made by the use of a datum frame model. The datum frame of the assembly is comprised of four datum curves created at the assembly level. Four arm.prt components are assembled relative to the four assembly datum curves. The design intent of this assembly is:
  
  
  • To have the four datum curves be the same length
  • To have the component arm.prt be a specified length longer than the datum curves to which it is assembled
  • To update the length of the springs as the angle of the lamp's arms change
  
  
  
• Figure 2 and Figure 3 show the symbolic dimensions of the features which need to be controlled to maintain the assembly design intent
  
  
• The dimensions were shown by clicking Tools > Relations and selecting the desired features in the assembly or assembly components
  
  
• In these figures, the four curve features in the main assembly were selected
  
  
• From within the Relations dialog box click Utilities > Switch Dimensions to toggle the dimensions from their symbolic representation to their numeric representation
  
  
• In Assembly mode, a shown dimension with its dimension type switched to a symbol will have the following annotation:
  
  "DIM_SYM:SESSION_ID"
  
  
• DIM_SYM is the dimension's symbol and COMP_SYM is the symbol number of the component that the dimension belongs to. In the above figures, "d18:1", "d19:1", "d24:1" and "d25:1" are the shown symbolic dimensions of the lengths of the four assembly datum curves and "d62:2" and "d78:2" and "d64:2" are the shown symbolic dimensions specific to the arm.prt component

Note: When replacing a component in a top-level assembly with one of its family table instances, the relation that drives a top-level assembly feature from a component dimension will not work unless the component ID is used in the relation. With this method, the symbolic dimensions would look like "d62:cid_79". This internal component ID may be found by clicking Info > Component, selecting the assembly component and then clicking Apply.

• An assembly relation file has three elements: the "Coding Table", relations and comments. The Coding Table is a table listing of component symbols and corresponding component names of all components referenced in the assembly relations. To open it click Show > Info from within the Relations dialog box. See Figure 4
  
  
• The relations are equations used to drive the geometry. Comments are manually entered text used to clarify the intent of relations preceded by "/*"
  
  
• In the relation file in Figure 5, the lengths of the datum curves are all set equal to one dimension, "d24:1" (as the coding table indicates, ":1" maps to a dimension contained in desk_lamp.asm), which is the first design intent. Next, the length of arm.prt, "D62:2" (:2 maps to arm.prt) is set equal to the same dimension controlling the datum curves, "D24:1", plus twice the distance to a datum plane in arm.prt, "D64:2", which was used to create the arm, then the distance of the two joint axis hole of arm.prt "d78:2" are controlled by the curve length "d24:1". The last section sets the length of the spring.prt equal to an analysis feature
  
  
• An analysis feature is a measurement which updates as the geometry changes. In this example, the analysis feature measures the distance between the two locating pins of the springs. The measurement will update as the angles of the lamps arm change
  
  
• Once proper relations have been established, assembly design intent can be maintained and propagated through the assembly structure while making minimal modifications at the top level assembly. The geometry shown in Figure 6 is the result of modifying one dimension, "D24:1"
  
  
• The geometry shown in Figure 7 is the result of modifying two angular dimensions ("d23:1" and "d26:1") which drive the four bar linkages. Notice, as the angles change, the springs update in length and location while keeping the numbers of coils constant