Constraint Limits in Inventor 201123 Sep, 2010 By: Rusty Belcher
Avatech Tricks Tutorial: Reach new limits with Inventor constraints by using the new capability to define limits to constraints.
Editor's note: This tutorial courtesy of Avatech Solutions.
Assembly constraints determine how components in an assembly fit together. As you apply constraints, you remove degrees of freedom, restricting the ways components can move. Autodesk Inventor 2011 allows you to assign maximum, minimum, and resting position values that specify the allowable range of motion for a constraint.
In this tutorial, I will demonstrate the process of adding constraint limits to new and existing constraints.
Identifying and Applying Constraint Limits
For the first part of this demonstration, I will be focusing on this actuator and defining the allowable stroke motion. As you can see, I have a hard limit at the back of the cylinder, and another limit where the linkage will collide.
Using the Measure command, I can determine the maximum allowable stroke for this design. Now I want to apply these limits to a constraint.
We will add the mate constraint as usual, selecting the opposite mating faces. Inventor 2011 has a new option available in the Constraint dialog box that allows users to define limits to constraints. Access the new option by clicking the More button, at the lower-right corner of the dialog.
The Constraint dialog box will then expand, exposing the new limit settings. You can determine a resting position and set a maximum and minimum limit for the constraint.
The resting limit uses the current offset value to determine the default position. I will enter the maximum limit I measured earlier, and leave the minimum value at zero. I then click OK to apply the new constraint.
As we drag the arm and test the constraint, you will see the limits restricting the movement of the components. A constraint with limits is identified in the browser by a +/- symbol.
What About Contact Sets?
Veteran Inventor users might ask why we just don't use the contact-sensitive approach. Contact sets require physical contact with other components to determine the limits. In contrast, constraint limits use assigned values to limit movement and do not require physical contact. Remember, we wanted to create limits based on avoiding contact. Constraint limits also require far less computer resources, allowing designers to create larger and more complex assembly simulations.
It is very easy to establish multiple constraint limits and create complex motion simulations.
Adding Limits to Existing Constraints
The next task in our demonstration is to limit the rotation angle of the chassis. I want to limit the rotation to 60 degrees on each side of zero. I already have an angle constraint locking the position of the chassis. To add a limit, I simply expand the More option and input the desired limitations. I will use the current angle value to determine the resting position. After applying the constraint, I will rotate the chassis and observe the limits I set. If I release the chassis, it snaps back to the resting position.
The new constraint limits option enhances the existing Inventor constraint workflow. Applying constraint limits based on a known or measured value is a handy improvement.