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Tangential Constraints

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Message 1 of 9
tmchenry
833 Views, 8 Replies

Tangential Constraints

I'm trying to build an assembly with conical rollers rolling on a cylindrical support.  Refer to the attached sketch.  I'd like to be able to constrain the conical faces of the roller to the cylindrical surface of the support.  It doesn't seem to be possible to do that in Inventor; or, more accurately, it's not possible to put a tangential constraint on both conical faces at the same time.  The first tangential constraint causes the part to place a generatrix line parallel to the axis of the cylinder.  (I had to look up what generatrix means, too.)  So it's not possible to make the second tangential constraint.

 

Anybody have any idea how I can do this?  Just in case that's not difficult enough, the reason I'm doing this is because, ultimately, the support will not be a plain cylinder but actually a tube that also curves.  It's the behaviour of the roller through various curves on the support tube that I ultimately want to model, but I have no hope of doing that if I can't even get the roller constrained onto a plain cylinder.

8 REPLIES 8
Message 2 of 9
JDMather
in reply to: tmchenry

Use Transistional Constraint or Dynamic Simulation Joint.

Attach your assembly here if you can't figure it out.


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Message 3 of 9
tmchenry
in reply to: tmchenry

I was able to apply a motion constraint, and also a tangential constraint between an axis on the tube and a sketch circle on the roller.  That reproduced the effect I want in a straight line.  But I can't figure out how to get it to follow a curved tube. I tried using a tangential constraint between the sketch circle and the sketch line that defined the path of the tube, but Inventor won't allow such a constraint.

 

I've attached a pack-n-go that shows what I've done.

Message 4 of 9
JDMather
in reply to: tmchenry

Tangent is only between two faces (on on each part).

If you have Shaded with Edges turned on you will see that your tube path is actually several faces.

 

Do you have Inventor Professional (Environments>Dynamic Simulation)?


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Message 5 of 9
JDMather
in reply to: JDMather

A second problem is that there would still be too many degrees of freedom

At it is if you could get this roller to stay on the rail, it could still rotate around the "axis" of the rail.

It is unlikely that represents your true real-world mechanism.

Is there an "up" position , another roller, another rail and roller with truck?

Something is missing?


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Message 6 of 9
tmchenry
in reply to: JDMather

Yes, ultimately there will be two rollers in a truck.  I'm actually hoping to use Inventor to help optimize the geometry of the truck.  To behave the way I want, the truck will probably have to be articulated, allowing relative motion between the axes of the rollers.  I can build and test mock-ups, but I was hoping to speed up the process by modeling it, instead.

 

It appears that we do not have Dynamic Simulation.  Would it be in Add-ins if we had it?

Message 7 of 9
JDMather
in reply to: tmchenry

Without Dynamic Simulation it is going to be a bit harder (and even with DS, there is a significant learning curve).

 

I would need a curve depicting the typical path of a point in the center of the roller to figure out how best to do this manually.

 

Just noticed that you are using r2010.

I would be reluctant to spend much time on a solution since you wouldn't be able to open my files, but sketch the path and I'll see if I can present images to a solution.


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Message 8 of 9
JDMather
in reply to: JDMather

I'm trying to determine if there is an always "up" postion.

Looking at the glass cube - would the roller always appear as a circle in these positions.

Is this Up as indicated?Up.PNG


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Message 9 of 9
tmchenry
in reply to: JDMather

Yes, the final constraint is gravity!  The rollers will always be more or less on top of the tube.  The force they resist will have a downward vertical component (gravity) and a horizontal component, with the vertical componennt being at least two or three times the horizontal component.

 

I've attached a typical tube configuration.

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