Constraining in AutoDesk Inventor

This is just one hub in a series of 15 hubs on using AutoDesk Inventor for 3D modeling. The index hub is here.

Once a model is complete, we need to actually start using it. That means we'll have to assemble it. If you don't assemble the parts, it only takes a simple click and drag to move them around. You may have noticed this already. However, Inventor lets you lock a part into place (grounding) or tell it to move in a certain direction only, or along a certain plane. This is handy for making models that move nicely, and critical in the analysis of kinematics.

In this tutorial you'll learn how to ground objects and constrain the motion of other objects. We're still using the same shelf that we made earlier, and the light that we added in the last tutorial. We'll take this light and make it ride along the rod it was designed for, and show you how it rotates and slides.

Grounding

The first thing we need to do is ground the shelf. Grounding is when you fix an object so that it doesn't move at all, regardless of direction. Using the shelf we made earlier, right-click on a part in the model tree on the left-hand side, or select the part in the 3D view and right click. You should get a menu like the one we got in Picture 1. Select "Grounded" to freeze the object right where it is. We'll do this for everything in our assembly except the light itself.

Constraining

Now we want to constrain the light. Click on the "Constrain" button under the "Assemble" tab, and take a look at the menu. Picture 2 shows what you should see. There are several options for constraining - the most important ones are the four on the left side. They are the "Mate," "Angle," "Tangent," and "Insert" constraints.

Their functions are fairly simple (although the application is not always as simple): The "Mate" option constrains two surfaces together, either flush or opposing. The "Angle" button sets parts at a certain angle from each other, and has three different options. The "Tangent" command lets objects roll on each other's surfaces, either inside or outside. The "Insert" option puts a bolt in a hole, and lets it rotate but not slide.

We'll use the "Mate" option, since the "Insert" option won't let the light slide up and down on its rod, and the mate option will work for curved surfaces as well. Click on the inner ring of the light socket, and then the ring around the rod. Make sure the dashed center line shows up as well, since we are trying to constrain these parts to move along that line. Click apply and see what happens. You might have to try several times, as constraining can be pretty fickle. If you don't like what happens after you hit apply, hit Ctrl+Z to undo the action, or look for the back arrow at the top left-hand side of the screen.

Once you have the light set, close the constraint box. Don't worry if the light is going through the shelf for right now, as seen in Picture 3. There is no collision detection on right now, and that's past the scope this tutorial anyway. Just grab the light and drag it around to get it out of the shelf. You might notice that the light wont' slide on the plane. If this is the case, find the light in the Model tree on the left hand side, expand it, and look for the "Flush" constraint. This constraint was created (at least in my case) when the part was first made. You can delete this constraint.

Now you should have a light that is properly constrained and looks like Picture 4. Good work! Try clicking and dragging to see where the light goes. You'll notice that it might slide past the end stops, but that's fixed with collision detection again, or even the limits option in the constraint section, neither of which is the object of this tutorial. Maybe someday I'll come back and add those sections.

Onward and forward - we've got to add some motion to this lamp, and then see what else lies ahead for analyzing and viewing!