Introduction to constraints

Constraints are a powerful tool in conceptual engineering. The engineer uses a design tool such as Pro Desktop to quickly create a model which represents his thoughts. As more information comes to hand, the model has constraints applied.

Constraints are similar to dimensions but are much more powerful.

As you draw simple objects such as rectangles and squares, geometric constraints are create automatically.

To view constraints

• from the design toolbar click

Dimensional constraints

As the name suggests, dimensional constraints are similar to dimensions in manual drafting.

Applying dimensional constraints in Pro Desktop can be a little tricky

Constraining a line

• select the sketch dimension tool from the design toolbar

• move the pointer over the line to prehighlight it

• click and hold the left mouse button

• drag the pointer away from the line

• release the mouse button to reveal the constraint

Constraining a rectangle

A rectangle may be constrained using two methods:

• length of sides
• distance between sides (preferred method)

Of these two methods, the distance between sides is the safest method. The size of the rectangle can not be changed unless the constraint is adjusted by the designer.

If the length of sides method is used, it will not continue to describe the rectangle if the corners of the rectangle are rounded

Using the length of sides method (not recommended but easy)

To apply the length of sides method, apply the steps described in constraining a line to both sides

To apply the distance between sides method, apply the steps described below in constraining distance between parallel lines to both sides

Constraining circles and arcs

Circles and arcs can be constrained using either diameter or radius.

Constraining a circle or arc with a radius

• select the sketch dimension from the design toolbar

• move the pointer over the circle/arc to prehighlight it

• click and hold the left mouse button (IMPORTANT - do not to click and release the button)

• drag the pointer away from the circle/arc

• release the mouse button to reveal the radius constraint

Constraining a circle or arc with a diameter

• select the sketch dimension tool from the design toolbar

• move the pointer over the circle/arc to prehighlight it

• click and release the left mouse button to select the circle/arc

• click the and hold the left mouse button

• drag the pointer away from the circle/arc

• release the mouse button to reveal the diameter constraint

Constraining an ellipse

Ellipses are constrained by defining the length of both the long and short axes.

To constrain one axis

• select the sketch dimension tool from the design toolbar

• move the pointer over the ellipse to prehighlight it

• move the pointer near the end of the axis you need to constrain - a black handle appears

• click and hold the left mouse button (IMPORTANT - do not to click and release the button)

• drag the pointer away from the ellipse

• release the mouse button to reveal the constraint

To constrain the other axis, repeat the above steps

Constraints between objects

To this point we have seen how to constrain individual objects. Since most designs consist of many objects, it is important to be able to define constraints between objects.

Distance between parallel lines

To constrain the distance between parallel lines

• select the sketch dimension tool from the design toolbar

• move the pointer over one of the lines to prehighlight it

• click on the line to select it

• move the pointer over the other line to prehighlight it

• click and hold the mouse button

• drag the pointer to position the constraint

• release the mouse button to reveal the constraint

Angle between inclined lines

• select the sketch dimension tool from the design toolbar

• move the pointer over one of the lines to prehighlight it

• click on the line to select it

• move the pointer over the next line to prehighlight it

• click and hold the mouse button

• drag the pointer to position the constraint

• release the mouse button to reveal the constraint

Distance between circle and line

Creating constraints with circles can be rather tricky. An important rule to remember is:

• if a constraining involves the centre, look for a black square at the centre when selecting the circle

• if the constraint does not involve the centre, avoid the black square at the centre when selecting the circle

Centre to line

• select the sketch dimension tool from the design toolbar

• move the pointer over the circle to prehighlight it

• when a black square appears in the centre of the circle

• click and release the left mouse button to select the circle

• move the pointer over the line to prehighlight it

• click and drag the pointer parallel to the line

• release the mouse button to reveal the constraint

Circumference to line

• select the sketch dimension tool from the design toolbar

• move the pointer over the circle to prehighlight it

• NOTE - be sure there is NOT a black square at the centre of the circle

• click and release the left mouse button to select the circle

• move the pointer over the line to prehighlight it

• click and drag the pointer parallel to the line

• release the mouse button to reveal the constraint

Distance between circle and circle

See the general rule stated above relating to constraining circles

To constrain the distance between the centres of two circles

• select the sketch dimension tool from the design toolbar

• move the pointer over the first circle to prehighlight it

  • NOTE - be sure there is a black square at the centre of the circle

• click and release the left mouse button to select the circle

• move the pointer over the second circle to prehighlight it

  • NOTE - be sure there is a black square at the centre of the circle

• click and drag the pointer away from the circles

• release the mouse button to reveal the constraint

Altering constraints

After completing a draft design, it becomes necessary to refine the model by altering the constraints.

To change a constraint:

• select the select constraints tool from the design menu

• move the pointer over the constraint to prehighlight it

• click the mouse once to select the constraint

• double click the constraint to open the properties dialog box

• change the value of the constraint

• click OK to confirm the new constraint value

• the size of the object or the distance between the objects will be adjusted