Design Rules Command Exercise
 

 

Pro/Desktop automatically captures values as you create objects such as length constraints in sketches and offset distances in assembly mating conditions. These values are termed design variables. You can create additional variables and mathematical expressions called Design Rules to create relationships between design variables and set relationship or quantitative conditions on the objects. Design variables and design rules can be displayed in drawings in callout groups linked to the object.

Simple Example of Design Rules

Sketch a 4 inch x 3 inch rectangle and extrude it 2 inches

This simple extruded box has four variables:

  • Length of the rectangle
  • Width of the rectangle
  • Extrusion Distance
  • Taper Angle

 

The Design Variables are identified as follows:

Name of the object they control \ name of the variable

This means the the length of the rectangle would be:

  • base\length 1

This identifies it as a variable in the base workplane called length 1.

Variable names can be viewed at Tools>Variables

The variable names are best displayed when exported to Excel.

Learn how to export variables to excel

This means that the complete list of variables for the extruded rectangle would be:

Variable Names
Length of the rectangle base\length 1
Width of the rectangle base\length 2
Extrusion Distance extrusion 1\distance
Taper Angle extrusion 1\taper

 

Design Rules allow relationships to be made between the design variables. For example you could relate the width and length of the rectangle to each other L=2*W

Make sure the initial sketch is active (double click the initial sketch in the object browser)

  • Tools>Design Rules
  • Double click the blank area next to the faded blue check mark to start a new design rule
  • Click in the blank area next to the green check mark to input the rule

 

There are two ways to get the design rule formula into Pro/D. You can either type the formula in using the variable names or you can select the variables with the Constraint selection tool. First, lets use the constraint tool

  • Click the constraint selection tool
  • Click on the length of the rectangle
  • This adds the clicked variable to the design rule formula.
  • NOTE 1: The variable name is highlighted. If you type anything, it will delete the variable name. Hit the right arrow key to unhighlight the variable.
  • NOTE 2: If the constraint you want is prehighlighted you must click off the constraint and then select it

 
  • Type in the = sign (remember if you didn't unhighlght the variable name it will delete it, see note 1)
  • Select the width with the constraint selection tool
  • Add a *2 to the end to complete the formula
  • Click the green check to enter the design rule. This will put the design rule into the big white area.

The design rule is now entered in. Change the width of the rectangle to see what happens. Hit the Update button to get the design to update based on your changes.

Try changing the length variable. Notice that the place to change the value is grayed out since the length is controlled by the design rule you just entered.

 

Now lets add a design rule that relates the extrusion distance to the width. (Ext dist=0.5W)

  • Tools>Design Rules
  • Double click next to the faded blue check mark
  • Click in the blank area next to the green check mark to enter in the new rule

You want to add that the extrusion distance is equal to half of the width. You cannot use the constraint selection tool to select the extrusion distance so you must TYPE in the variable name. See the above table for the variable names.

Now change the width and see how it controls both the length and the extrusion distance

This completes the introduction to design rules. The sky is the limit in the usage of design rules.

Advanced Design Rule Features

Built-in mathematical functions allow you to create sophisticated design rules. You also can create conditional design rules that in an IF-THEN-ELSE format, and applicable logical operations to capture your design intent.
 
Function
Expression
Sine sin(x)
Cosine cos(x)
Tangent tan(x)
Arcsine asin(x)
Arccosine acos(x)
Arctangent atan(x)
Logarithm log(x)
Logartithm to base 10 log10(x)
Square root sqrt(x)
Power ^x

where x is a number or variable name

About Conditional Design Rules

Pro/Desktop allows the creation of conditional design rules. A good example of a conditional is a classic if-then-else expressions.

To create a conditional design rule, use the following format:

IF (logical expression, expression1,expression2)
IF(logical expression, do this if true, do this if false)

Where:

  • logical expression is the condition to be met (required)
  • expression1 is the result if the logical expression is true (required)
  • expression2 is the result if the logical expression is false (optional)
  • expression1 and expression2 are expressions created using the regular non-conditional format.
  • If expression1 is true, expression2 is ignored.
  • If there is no expression2 and expression1 is false, the design rule is ignored

The logical expression can include the following logical conditional operators :

  • AND
  • OR
  • IF

 

The logical expression can include the following mathematical conditional operators:

< Less than
<= Less than or equal to
> Greater than
>= Greater than of equal to
= Equal to
<> Not equal to

 

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Tutorial written by Steve Schweitzer