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Flexible hose and minimum radius of curvature

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DavidDEC

Mechanical
Jun 8, 2010
15
Hello,

I'm trying to find some kind of workflow to succesfully design flexible hoses that fit into place from the beginning using the Routing Mechanical module. I'm currently using NX 4.

The main problem is that I haven't found any tool that allows spline generation AND curvature control at the same time. This results many times in hoses that once in the shop don't fit well at all between their connections. The flexible hose supplier needs to come, take some measurements and manufacture another hose. Sometimes, there isn't even the possibility to do this because no hose will fit in some thight assemblies.

Shoudn't the Routing Mechanical module be a help in these situation?

This is what I have been trying:

You only have the "slack direction" option to have some control of the shape. This option is realistic if you are to simulate the influence of gravity on a very soft, very large hose.

However, when space is tight and the shape of the hose comes from bending it to its minimum radius of curvature, the "slack direction" option becomes completely unrealistic. Let's take an "S" bend, in this case one of the two curves would have a fair curvature, while the one that is the oppsite direction of the slack would have a very tight radius.

The only workaround I've found is to create the paths with the "generate splines" option off. Then I start checking in an interative process if I can assign a given minimum bend radius to each corner.

Isn't there any more straightforward method? Something that given two endpoints with their respective slopes gives you a spline that respects a minimum radius of curvature?

Thank you in advance
 
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You have run across an OLD (UG v10) issue that has never been resolved. This enhancement was requested years ago and "will be addressed on the next release". By seeing how sparse the responses to your query is, I suspect that others have read and, "AH YES!" but have chosen to remain incognito. One question I have is, on the S bends are you restraining them physically at all 3 tangencies? If not the the minimum bend R is a SWAG anyway.
 
Hi wecurb

Thanks a lot for your reply, and sorry for the time taken to rewrite.

Answering to your question, I'm testing a new workaround which is to forget completely about the Routing module, and draw the path in a Skectch. I know this is not straightforward at all, but it is working as means of understanding a little bit what goes on with the hoses.

In the sketch, in order to create an -S- bend I don't draw just 2 arcs and 3 tangencies (this way we would get the SWAG you mentioned). I add 2 more arcs in the end points that start with an opposite curvature of that of the main arcs. Please, see the image in order to understand this explanation. This way I get more degrees of freedom and a shape very similar to what there is in real life. I constrain that arcs in the endpoints to have the minimum radius of curvature of the hose, and then I constrain the 4 arcs to have a given perimeter value.

The perimeter is in the end one of the main parameters I want to control, the other one is the minimum curvature. Routing mechanical only gives you control of the first one, and Routing electrical allows you to check if the second one is ok with a set of company rules.

You can compare the result from the sketch versus the Routing Mechanical 'solution' in the last image. The skectch gives you a lot of control but is hard to implement if you want a dynamic process for designing assemblies with hoses.



Again if anyone has a good workaround for this issue, it would be nice to know, and if anyone from UGS can say if and how they're gonna solve this it would also be appreciated. I have to mention that a program as old as Catia V4 had a fair algorythm for drawing realistic enough hoses..
 
 http://files.engineering.com/getfile.aspx?folder=9b670cc8-db99-4c2d-b9e9-bffc0d3115d3&file=hoses.pdf
I very rarely draw hoses, but its always 3d routing and I start by having a line at each connector and then drawing a bridge curve between the two lines. If the hose is routed around corners, etc, I create a short line at any point where I need to influence its shape/position.

There is a minimum radius control in bridge curves, but I have had NO LUCK in being able to actually use it. See my thread:

NX 7.5.0.32 MoldWizard
 
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