CADquest Article Series

Featured in "Pro/E The Magazine", June 1998

Pattern Relations

Patterns are a common technique to copy a series of features in Pro/ENGINEER. Often the geometry requires the use of pattern tables because the pattern is not constant. Other patterns such as staggered patterns can be created using pattern relations. This technique is not used as often as it could be. Relations as an alternate to dimensions or tables can control all types of patterns (Identical, Varying, and General).

Pattern relations can be used to create offset or staggered patterns similar to those found in RS-232 style connectors. A simple example of a staggered pattern driven by pattern relations is shown in Figure 1.



Figure 1

Pro/ENGINEER has pre-defined system parameters that you can use when writing pattern relations, these are called ‘pattern parameters’. Each dimension used in a dimensional pattern can have relations written to control it, and each dimension has separate pattern parameters.

You can vary one dimension using a standard increment value and another using pattern relations in the same pattern if so desired.

The pattern parameters are listed here: LEAD_V defines the original feature’s locating dimension

MEMB_V defines the location of the instances with respect to the reference of the leader of the pattern (a dimension from where the leader is dimensioned from to the instance)

MEMB_I defines the increment dimension of the pattern

IDX1 defines the instance index value for each instance in the first direction. The leader is assigned 0 (zero) and increments by 1 (one) for each instance.

IDX2 defines the instance index value for each instance in the second direction. The leader is assigned 0 (zero) and increments by 1 (one) for each instance. Figure 2 shows the pattern parameters for the first direction. Identical parameters also exist for the second direction.



Figure 2

Prepare the Part

Create the part and the feature to be patterned. Like any feature to be patterned, the feature must have a locating dimension, and in this case, two locating dimensions.

The example we will use is a simple block with a staggered pattern of holes. Create a block part and place a linear hole through the part as shown in Figure 3.



Figure 3

Create the Pattern

To create a staggered pattern, use only one direction, and use two dimensions. Write relations for one of these dimensions to cause the staggered effect. Start your pattern like any other dimensional pattern. Pick #Feature; #Pattern; select the hole, pick #Done; #Relation; select the 25.00 dimension locating the hole from the top of the block. Pick #Edit, and add the relations.

When you repeatedly raise negative one to an incrementing value (like IDX1), you create an alternator, which causes the stagger. In this example, (lead_v)*(2) sets the distance of the staggered row of the pattern. This can be any value and does not have to use lead_v.

off = -1^IDX1

if off <1

memb_v = (lead_v)*(2)

else

memb_v = lead_v

endif

After you save and quit from the editor, pick #Done; #Value, and select the 20.00 dimension locating the hole form the end of the block. Enter <20> for the increment dimension, pick #Done, then enter <9> for the number of instances. To finish the pattern, pick #Done. The result is shown in Figure 4.

Note: Either MEMB_V or MEMB_I must appear in the relation, but they cannot both appear in the same relation together.



Figure 4

Conclusion

Staggered and offset patterns are easily created using pattern relations. Existing patterns can be #Redefined to be driven by pattern relations. To modify pattern relations use #Relations; #Pattern Rel; pick one of the instances; then from the DRIVER DIMS menu select the d# shown, then pick #Edit Rels.

Steven G. Smith, CADquest, Harrisburg, PA