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An Introduction to Inventor Joints

by Bryce Ochoa on Nov 19, 2015

00joint_pic.png

Challenge:

I have too many constraints (relationships) in my assembly, how can I streamline my assembly and lower the amount of relationships I have?

Solution:

The solution is the Joint relationship inside of Inventor 2016. The Joint feature can create relationships between parts that would otherwise take two or even three constraints.

First, go to the “Assemble” tab, and select the “Joint” icon, if it’s not visible you may have to expand the Relationships panel to see it.

01tool_bar-_joint.png

 The Joint command dialogue box will appear:

02joint_dialogue_box.png

Similar to the Constrain dialogue box, it will ask for the user to select the two part features to apply the joint to and what type of joint to apply.

03joint_type.png

The default connection type is Automatic. Automatic determines the joint type based on the following rules:

  • Rotational is selected if the two selected origins are circular
  • Cylindrical is selected if the two selected origins are points on a cylinder
  • Ball is selected if the two selected origins are points on a sphere
  • Rigid is selected for all other origin selections

For moving joints, selection order is important. You’ll want to be sure to select the origin on the moving component first and the origin on the stationary component second. If necessary, change the joint type and click apply. When you do, the program displays a small simulation of how the parts will interact with the selected joint type.

Now, how does this help to streamline my work flow? Well, if you were to use Constraints to get the desired behavior of the roller joint in it would take one Tangent, a Flush, and Insert applied between the pin and arm and pin and roller. This comes out to be a total of 5 relationships for one joint!

05overconstrained_edited_example.png

If you were to instead use Joints to the same roller joint between the pin and arm and the pin and roller, it would only take 3 relationships total when you include the Tangent Constraint. This comes out roughly to be a 1:2 ratio between the number of Joints used compared to Constraints used.

04joint_pic_edited.png

This may not seem significant now, but if you work with large assembly files with a multitude of different parts and subassemblies, the number of relationships you use can grow fairly quickly. By using Joints, you can easily “clean up” your assemblies and reduce the total amount of relationships greatly. In the example below, the assembly that didn’t use any joints had a total of 45 relationships. The assembly using joints had only 29 total relationships.

06Compare.png

So go ahead and try this out on your own and see for yourself how it can help you in the future.

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Topics: Autodesk Inventor, v2016, Tech Tips, Joints

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