July 11, 2013

Posted on July 11, 2013 by Bob Reid, Manufacturing Solutions Engineer:

Error:  Autodesk Inventor Professional – Place/Edit Constraint

When you are trying to constrain two parts together, why does the following error dialog box pop up?

Likely, the dimensions are just slightly off.  The following trick I use is a Pillow Block, downloaded off the internet, and a mounting plate that was modeled in Inventor constrained together with the different dimension values.
1.  I downloaded a pillow block that has a center distance of 4.38 inches.  It is quite common for parts on the internet to be rounded to only two decimal places.

2.  The mounting plate I created has a center distance of 4.375 in.  If I try to constrain the two parts together, I will receive an error because the dimensions are not the same.  This is where I can use the Constraint Limits to override the non-matching values.

3.  I create two axially constraints with the holes and a standard Mate-Mate with the top of the mounting plate, and bottom face of the bearing:

4.  If I try to constrain the two axially mates first, I receive the error because my dimensions are off by .005 in.

5.  To fix this, I add a limit to my constraint to allow me to override the .005 in difference between the two parts:

6.  I click apply and the constraint is applied.
7.  In the Model Browser, the constraint is shown with a +/- after the constraint to show that it has a Limit to it:

8.  A close-up view of the holes will actually show that the holes are eccentric:

PLEASE NOTE:  This is a trick that I use within Inventor for examples that I have shown above.  The actual purpose of the Constraint Limits is to specify the range of motion for the Components that move or rotate.
From the Autodesk Help File:

What are constraint limits?

Constraint limits use the specified values to define the allowable range of motion for components that move or rotate.  You can specify a Maximum, a Minimum, and a Resting Position for a constraint in the Assembly tab.  The Resting Position uses the value specified in the Offset box.  A constraint with limits is identified in the browser by a +/- symbol.

Contact sets require physical contact with other components to determine the limits.  Constraint limits use assigned values to limit movement and do not require physical contact.  Use constraint limits to evaluate a design based on knowing maximum, minimum, and resting values.

I hope that helps you get past the error messages.  If not, contact us and we will find out what else might be going on in the design.
See some of Bob’s previous posts:

Robert Reid graduated from Middlesex College in New Jersey with a Degree in Mechanical Engineering Technology. With over 25 years of Industrial Machine Design, including Wire Drawing Machinery, Plastic Processing Machinery, & Packaging Machinery, Robert has held various positions within the workforce, including, Manager of Engineering; Sheet Extrusion Dept, Manager of Engineering, Chief Design Engineer. He is currently an Autodesk Inventor Certified Expert.
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