tangent between two curved srufaces

[Anonymous]

The tangent constraint between two curved surfaces in Inventor is very confusing. I have never been able to get the position I wanted.

For example, I would like to make a tangent contact between the two links as follows:

If I select the green and blue surfaces, the link will fly to this wierd position. I though the word "tangent" at least means two things are touching each other, why are the two surfaces driven further away??

If I select the other "solution"(internal tangent), this is what I get:

Keep clicking that button, the link can acutally fly around~~but none of the postions is "tangent" to the green surface

  

If someone can provide a detailed explanation of this tangent constraint, and tell me how to make it right, I'll be very grateful.

[blair · Accepted solution]

You actually have 2 tangents for each end of the loop. The first is the solid and the second is the swept path. I've never been able to get the tangent to work properly when putting together a looped chain with links.

I end up resorting to creating work points and using them. 

Spoiler

[SBix26]

Constraints are geometric mathematical constructs, not reality.  Surfaces participating in a constraint are considered to be geometric entities.  For example a flat face of a part, for constraint purposes, is a plane, infinite in all directions.  In the same way, these half loop faces are actually circular tori (plural of torus) for constraint purposes, so what you are seeing is mathematically accurate, just not very helpful in making this behave like real solid objects.

I would do as Blair suggested and use some other geometry to help constrain them (angles with limits, work points, origin planes, etc.).  For a closer simulation of real-world behavior, you can use contact sets, but they are computationally intensive and make Inventor sweat (mathematically speaking, of course).  Contact sets do not take into account friction and gravity, so are still not as much like the material world as we would like.

Disclaimer: this is all just my observation and deduction from thirteen years of Inventor use, not because I have any inside knowledge!

Hope that helps,

Sam B

Inventor Professional 2016 R3 SP2
Vault Basic 2016 SP1
Windows 7 Enterprise 64-bit, SP1

[TheCADWhisperer]

What is your ultimate design intent?

You might need to progress over into Environments>Dynamic Simulation if it is more than simple assembly.

[Curtis_Waguespack]

H iziyin.w,

It's beem a long time since I looked at this model, but cbliss.com has chain example that you might look at, if you've not already done so.

I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com

Click thumbnail to open a zip file:

[Anonymous]

Thank you all for your kind suggestions. So I'll mark it as a "no-shortcut" problem in Inventor.

Thank you Curtis for the chain example, it's beautifully modelled. And your blog is fantastic!

[Anonymous]

Hello, I have tried to understand how did the author do the mate constrains between the chain links, but I couldn't. And what is the purpose of the angle constrain and how did he place it? Thankyou atajabbas Inventor 2020

[johnsonshiue]

Hi Folks,

Let me elaborate on the Tangent constraint behavior a bit here. Inventor assembly Tangent constraint actually operates on the base faces. For example, the tangent target faces are two half torodial faces. What is being solved is the full torodial face. So, it may look odd as if the faces are constrained in the air. The behavior is meant to make Tangent less restrictive.

Many thanks!