Inventor 2016 - Constraint Limits

By Gus Petrikas

Constraint limits are something that not every Inventor user is aware of, but something that is very useful when working with assemblies.

In short, constraint limits allow  a part to be constrained to another part but also allow it to move, at the same time restricting the assembly's movement to a certain point. This is where most of the Autodesk Inventor users would use the "Contact Solver" which is a resource-heavy function, whereas a constraint limit is just a parameter and is much easier on CPU and RAM usage.

Constraint limits can be found in the "Place Constraint" dialog box. Expand the window by clicking the two arrows and you will be presented with a couple of options to limit the constraint

Once a limit is applied to a constraint, the constraint name with a "+/-" sign will appear in the browser.

Here are some examples on how to use constraint limits:

Angular Constraint Limits.

Here is a simple setup of two parts that have been constrained together to create a simple hinge. The red part is grounded and the green part will rotate around the cylindrical axis.

Let us apply an angular constraint with Maximum Limit of 30°

This allows our green part rotate 0° to 30° each way in a smooth motion.

Now if Minimum Limit is set to 30°, that restricts the movement to +30° and -30° only, therefore, the green part now moves more like a switch - it "jumps" from one side to the other.

If "Use Angle As Resting Position" is selected, and the green hinge is moved, the constrained part will "bounce" back to its resting position - the angle it was originally constrained to.

Mate Constraint.

Similarly, limits can be applied to other constraints as well. This is the Shock Absorber assembly from the "Dynamic Spring" tutorial. I have applied a mate constraint between the top and the bottom parts of the shock absorber in order to restrict the vertical movement and set its resting position.

This results in the top part only being able to move 30mm upwards and 70mm downwards. It will come back to its resting position of 170mm.

Lastly, here is another example where limits come in handy, a covered toggle switch, also known as a "Doomsday Switch". Note that Contact Solver is off, meaning that movements are only restricted by the constraint limit function.