Linear motion design strategies

Hi all,

I've been using Inventor for about a 2 weeks now and I've hit a bit of a road block. It's the first CAD tool I've ever used and spent quite a bit of time learning it but I've reached the point where I'm out of ideas on how to tackle a certain problem. The overall goal here is to create a 3-axis CNC machine which uses rails and a lead screw to move the axes.

The objective is to rotate a lead screw which causes the nut on it to move along the lead screw axis. Attached to the nut is some kind of rectangular rod (it can be anything) but this rod is connected to some blocks on rails. The end result is simply: lead screw rotates, blocks on rails move.

I've attached some files if anyone is interested in seeing them but feel free to ignore 'em.

I've managed to get the lead screw to rotate and have the blocks on the rails rotate but it's only by brute forcing all combinations before it worked so there definitely wasn't any kind of engineering going on there. The main issue I'm having is constraining the nut on the lead screw to a parallel surface (ie. the blocks) to force the nut from rotating. Every time I try to add that constraint it says something is conflicting. When I try and diagnose the problem, pretty much any constraint I disable to get it to work is a vital constraint.

The second issue I'm having is drive constraints. When I drive the constraint that mates the front of the nut to the front of the lead screw mounting bracket it moves parts in the opposite direction. Basically, when I use the drive constraint, the lead screw rotates, the nut moves forward but the blocks on the rails move the opposite direction. When I use my mouse to rotate the lead screw however, the nuts and the blocks on the rails move together as I intended.

There's a few things I don't quite understand. The biggest one is mating the lead screw to the nut. For some reason I've had to mate it using the "mate" constraint and not the "insert" constraint. Whenever I use the insert constraint, it locks the lead screw and I'm unable to rotate it using the mouse. However, when I do this, it causes the drive constraint to work correctly.

I'm not looking for the most mechanically sound solution here (maybe I shouldn't be using Inventor for this?). I'm more looking for a way to design this machine so I can see and play with the measurements before I go building it. The biggest requirement though is that the parts move in the right directions and that the lengths, widths, depths and diameters are correct. I don't need to worry about torque or metal strength, etc..

Look forward to hearing your responses.

Cheers

cnc1.zip

cnc2.zip

I've just found a previous thread that looks like it answers my questions. Sorry for the thread!

Hi all,

I've been using Inventor for about a 2 weeks now ....... and spent quite a bit of time learning it ....

.....

Look forward to hearing your responses.

 

Cheers

2 weeks is a long time? I guess you found the Translation/Rotation constraint.

Look for any constraints with ! in yellow triangle and delete them and try again.

This one should be pretty easy once you figure it out.

Mate axis to axis (cylinders to holes) rather than Insert if there is supposed to be translation (straight line motion) remaining degree of freedom in addition to rotation.

Sort of got it working! Not really sure how to drive them all at once but I'll get there. Thanks!

Not really sure how to drive them all at once but I'll get there. Thanks!

Add a Directed Angle constraint to each lead screw (relative to base plate).

In Inventor Studio use the Animate Constraint for time period and angle (revolutions) to drive the screws.

or

better yet, if you have Inventor Professional with Dynamic Simulation you would have more control, but more complex to learn. The Inventor Studio method is easier to learn.

Excellent, Inventor Studio was pretty easy to work out, thanks!