topic Constraint Hierarchy in Inventor Forum

Constraint Hierarchy

Anonymous — Thu, 06 Jun 2019 14:21:42 GMT

Good morning,

I am working in an assembly with 3 parts (each a 2D surface patch), I placed the 2 gears (left one grounded), second one Flush to same plane, spaced using mate at 4.4375" (gear center distance). I created a tangent constraint at gear face edge, added a rotation motion constrain between the 2 gears and then deleted the tangent constraint. I could rotate the first gear around the second no problem, worked as intended.

I then added the link to the model, mated the point and axis to the left gear.

When I mate the point of the linkage to the point of the center gear, the rotation motion constraint relative to each other fails and the right gear rotates with respect to the link, but not the left gear.

Is there a hierarchy for constraints?

Thanks,

Re: Constraint Hierarchy

swalton — Thu, 06 Jun 2019 14:57:52 GMT

As I understand it, Inventor solves all constraints as a simultaneous set of equations. There is no hierarchy.

If you can, please Pack-n-Go the assembly and post your files. If you can't post these files, make up a quick example that you can post. It is much easier to troubleshoot native files, rather than pictures.

Does your link center dimension match your Mate1 center distance to 8 decimals (max precision on the measure tool)?

I would delete Mate1 after you get your link in the assembly. In the real world, the link will control the gear center distance, so build your assembly that way.

Re: Constraint Hierarchy

Anonymous — Thu, 06 Jun 2019 15:40:58 GMT

Hi S.,

I have attached the files as requested,

The dimensions matched as stated.

I deleted the First Mate (this is not a cruise ship...) and then added a mate to the link and right gear and got the same result... I am puzzled...

Thank you very much,

Re: Constraint Hierarchy

swalton — Thu, 06 Jun 2019 16:53:44 GMT

I'm using Inventor 2019.4, not 2018 so you won't be able to open my files.

What I see:

I can add the mate constraint between the link and the moving gear.
I can rotate the moving gear around the fixed gear, if I click on the moving gear. The link follows as expected.
If I grab the link with my mouse, I can rotate it around the fixed gear, and the moving gear follows. However, the moving gear does not rotate. It behaves as if there is not a rotation constraint between the two gears.

Are you seeing case 3, or some other unexpected result.

Re: Constraint Hierarchy

Anonymous — Thu, 06 Jun 2019 17:01:40 GMT

I am seeing case 3,

I want to rotate using the link, because when zoomed in tightly, it is very difficult to control the position of the right gear when moving around the left (fixed one)

(He broke the ship, he broke the bloody ship...)

Re: Constraint Hierarchy

j.palmeL29YX — Thu, 06 Jun 2019 17:43:13 GMT

I'd suggest to avoid the Motion Constraint (it causes a lot of problems) and use appropriate Angle Constraints instead. (between Tooth Shape1 and Linkage to drive the mechanism and between Linkage and Tooth Shape2).

Here you can see the result.

Re: Constraint Hierarchy

Anonymous — Thu, 06 Jun 2019 17:56:52 GMT

Jurgen,

That is excellent, I was trying to rotate it manually without having to use the drive constraint command, but I am sure I can reduce (control) the angular step in the drive constraint command to get to the position I am interested in.

Thank you very much,