Screw or thread constraint. 3

[skanskan]

Hello.

Is there any constraint, at the assembly application, to constraint a male thread to a female thread, or a screw to its bolt, or a vise screw to the screwed hole, in such a way that when you turn it it automatically suffer an advance in the direction of the axis of the thread?

I don't mean at the motion simulation but just at the assembly application.

 

[JohnRBaker]

NO.

John R. Baker, P.E.
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[skanskan]

Can't I constrain the helix to follow another helix?

 

[cowski]

No. The primary purpose of assembly constraints is to hold components in the assembled position, not creating animations (though there is some limited ability to do so).

Perhaps you should look into the motion simulation module...

www.nxjournaling.com

 

[JohnRBaker]

Now if there is a design consideration issue here, one could create a pair of constraints, one that controlled the offset or linear positioning of say the jaws in your 'vise' example, and a second constraint controlling the rotation of the Acme threaded-shaft. Now you could create a relationship, using expressions, between the angle of rotation of the threaded shaft and the linear motion of the jaw so that if you rotated the shaft a certain number of turns that the jaw would move a certain distance. However, there would still be NO DIRECT constraint between the male-threads on the shaft and the female-threads in the jaw, but the effect would be the same.

John R. Baker, P.E.
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[skanskan]

But can I create constraint relationships using equations from the assembly (without going into the motion simulation)?

 

[skanskan]

If you set the distance (numerically or dragging) then the angle will automatically be deduced from it (with a modular operation) but the opposite could be a problem, if you provide the value of the angle how can NX know the distance? many values could be possible.
Then I will define the distance as a numeric value, and the angle as a function of the distance but I don't know if the assembly is going to respond properly when I rotate the escrew.

 

[aluminum2]

Yeah, those sets of expressions and contraints sound a lot like the rack and pinion assembly constraint that low level CAD systems have had for almost a decade now.

 

[JohnRBaker]

Here is an example where I used the Constraint/Expression scheme that I mentioned earlier, in this case it's an Assembly of part of a Shaper. I set it up so that turning the handle raises the tool-holder. I then created a movie (see attached) using the Animation capabilities of NX.

John R. Baker, P.E.
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[skanskan]

What about constraining a point to follow a curve (the helix)?

 

[JohnRBaker]

OK, I worked it out and while the 'point on curve' suggestion got me thinking, it turns out that it really doesn't work all that well in practice but it did give me an idea. So I went ahead and modeled 'male' ('power screw') and 'female' ('nut') threaded parts, assembled them and applied the appropriate constraints (the 'power screw' is constrained to a fixed location but is allowed to rotate while the 'nut' was constrained so as not to rotate but is free to traverse). In my model I used ACME threads as they're the most common for drive-screw applications. Now you can't really make the faces of the two threads tangent as it's just to complicated for the solver since there are theoretically an infinite number of tangent points. So I reduced it to just ONE SINGLE tangent point, in this case a small spherical body was created tangent to the face of the 'female' thread in the 'nut' and it was THIS spherical face that I constrained to be tangent to the face of the 'male' thread of the 'power screw'. Anyway, this works great and the Constraint solver had no problems whatsoever with this. I then created an Assembly Sequence where I rotated the 'power screw' resulting in the 'nut' traversing along its axis.

Attached is a video showing the playback of the Assembly Sequence. Note that this was NOT done using the Animation function but rather using ONLY Assembly modeling. This is a real Assembly with real constraints. If anyone wishes, I can also upload the Assembly (it's modeled in NX 8.5).

So skanskan, take a look at the movie and see if this is what you were looking for.

John R. Baker, P.E.
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Product Engineering Software
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[skanskan]

Nice, and clever.
Could you please upload the assembly, please?
I'll study it.

 

[JohnRBaker]

OK, a zip file containing the Assembly and its Components is attached. To see it 'animate', after opening the Assembly, go to...

Assemblies -> Sequence...

...and when the Sequence task starts, press the 'Enter' button to play the Sequence.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
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To an Engineer, the glass is twice as big as it needs to be.

 

[skanskan]

It works well.
I've also tried making a point (on the screw) follow an helix while the axis is always aligned with one direction and it doesn't work well.
But if just create a sphere and force its center to follow a line it works well, I don't know why.

 

[uwam2ie]

thank you John,
I tried to recreate in squencing - no success , can you offer a avi how you had created it?
thanks in advance

 

[JohnRBaker]

Do you mean that you can't 'playback' the Assembly Sequence in the Assembly I uploaded?

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
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Siemens PLM:
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To an Engineer, the glass is twice as big as it needs to be.

 

[uwam2ie]

no playback works ,
I have tried to recreate with no success, how do you create, set up the rotation, that it looks so nice?
TIA

 

[JohnRBaker]

First off, if you're trying to create any sort of kinematic 'simulation' your Assembly must have some degrees-of-freedom, that is you could manually drag a Component using the...

Assemblies -> Component Position -> Move Component...

...function and it would 'articulate', honoring the Assembly Constraints. If you can do that, then you can use Assembly Sequencing to 'drive' your assembly as if it were a mechanism.

So start Assembly Sequencing and create a new sequence. Then select the first icon on the toolbar below titled 'Insert Motion' and when the dialog bar comes up, select the Component that you want to 'drive' and then select the next icon, titled 'Move Object' and when the 'drag handles' appear select the one that represents the motion that you wish to apply (note that you can only apply a motion that can actually be performed meaning that even if all the handles are displayed, only one or two might actually be applicable so you really should experiment ahead of time, as I suggested above, using the Move Component function to get a feel for what works and what doesn't). When you select a handle an entry widget will appear where you can enter the amount of movement that you wish to apply. For example, in my threaded-rod case, I select the handle that would rotate the threaded-rod about its axis and then entered the number of degrees that I want it to move, in this case it was 12,000° which gave me approximately 33 rotations. Note that you can enter positive or negative values, just that you can't enter any value which would cause a motion that would exceed the degree-of-freedom. In this case, anything much over 33 rotations would have exceeded how far the threaded-rod could move before it ran out of the nut.

Once you see the preview and if it was OK, then select the 'green' checkmark to accept the motion and you can play it back using the 'VCR' buttons in the toolbar. Note that you can also enter 'camera' postions by rotating the image before or after any motion and hitting the 'Camera' icon in the 'Insert Motion' toolbar dialog, to save that 'point of view'. This way you can get the sequence to zoom in or out, or move around during the sequence playback. To remove individual motions or cameras, open the Sequence Navigator 'tab' on the 'Resource Bar'. You can delete motions and cameras by selecting them and press MB3 and selecting 'Delete'.

Anyway, play with it a bit and you should get the hang of it.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[Axis2084]

Wow John, this looks precisely like may different things I'm trying to make, I'm a little fuzzy as to how. Can the be done in NX8? could you re-add the asm file in NX8 so i can open it and learn how you did it.

PS i learned from one of your past knurl files to great success.

Thanks for all you do!

 

[JohnRBaker]

OK, I've attached an NX 8.0 version of the assembly (note that the parts were not remodeled, I simple did a Parasolid export out of NX 8.5 and into NX 8.0 so as to save time and created a new Assembly and sequence). Everything is the same as explained in previous posts above.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.