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Multiple sub-level mechanisms do not function in top level assembly

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Multiple sub-level mechanisms do not function in top level assembly

Platform: Creo 2.0 M030

Problem: Mechanism constraints broken on a simple assembly with two synchronized hydraulic cylinders that extend/retract and pivot around a common axis.

http://content.screencast.com/users/mr.shaun/folders/Jing/media/4cfc4aac-7484-4887-ac17-785ed567b8cc/2013-11-07_1733.png

Additionally, there is a guide-plate that controls the arc of the devices on the ends of the cylinders. That guide plate also has the ability to move back and forth in a slot. The model did at one point perform nearly as intended.

I would appreciate some feedback on how this assembly could be created.

Thanks!

1 ACCEPTED SOLUTION

Accepted Solutions

Re: Multiple sub-level mechanisms do not function in top level assembly

Hey Shaun,

I just took a smaple look at 5000-400-a17000.asm - and this basic assembly already has connection error. problem seems to be in a bad tangent constraint, between the 2 first components, that also seem to be a wrong one - pin goes through the whoel solid material.

In top assembly you just inherit same error.

I changed tangent to Coincedent (aligns slot side with a hole) and error goes away - also in top assembly. Try putting the fixed assembly into your data and check if top assembly works better.

Regards

- Vlad

39 REPLIES 39

Re: Multiple sub-level mechanisms do not function in top level assembly

I never liked that little "disconnnected" error.

The only thing someone pointed out that fixes this is by starting with a "snapshot" in order to "reset" the assembly.

Re: Multiple sub-level mechanisms do not function in top level assembly

And welcome to the forum, Shaun!

Re: Multiple sub-level mechanisms do not function in top level assembly

I discovered snapshots after the assy failed - I'll definitely explore that in the future.

Re: Multiple sub-level mechanisms do not function in top level assembly

Wow... this really is a convoluted mess. I finally got rid of the error. I had to remove all the connections at all levels and replaced them with fixed.

You might also explore setting the regeneration value in the connection assembly constraints.

I for one would -really- like PTC tech support to weigh in on this thread on how to best zero on this type of disconnected failure.

It seems we are simply flying blind in trying to resolve issues such as this.

I went so far as to begin deleting components and I was down to 3 components and the it required fixing to remove the error. Of course, it wasn't the -only- error.

Re: Multiple sub-level mechanisms do not function in top level assembly

Shaun,

Here are some general notes on connections and related errors in Mechanism design - see if this may help you. Given you talk about sub-level mechanisms problems in top level assembly this might be related to disruption in bodies scheme / body locks.

http://communities.ptc.com/message/222656#222656

Regards

- Vlad

Re: Multiple sub-level mechanisms do not function in top level assembly

Vladimir; I really appreciate the insight you provided in the linked post. I read it at the time and it makes perfect sense.

I think here is a different issue. Yes, the model is a mess (sorry Shaun!), and when you are in this state, where do you even begin to clean it up? Shouldn't there be -some- kind of log that tells you where the "disconnected" error emanates from?

Consider this scenario:

Someone left an assembly file in a lousy state and they went off on their new job and left me to resolve it during a routine Engineering Change Order operation. Now, rather that a 10 minute drawing update, I have a 2-3 day assembly rebuild to do and probably a fully messed up exploded assembly drawing, assuming I even know -how- it was meant to work in the 1st place.

This is all too common. When you contract with someone to do simple work, then telling them that their files are a mess is typically cause to get you replaced in a hurry. Clients just want -results-!

Is there not any kind of diagnostic tool within Creo that can help sort out these types of constraint errors? Model tree columns that will highlight the failure? "FIXIT" button?

In the case of the file included in this thread, the sub-components do not fail on their own, they fail at the top level. But no indication what-so-ever as to -what- is failing. Someone probably dragged a component and things cannot be put back where they were... and then they saved it! ...and purged the previous versions. Etc.

Re: Multiple sub-level mechanisms do not function in top level assembly

Antonius Dirriwachter wrote:

In the case of the file included in this thread, the sub-components do not fail on their own, they fail at the top level. But no indication what-so-ever as to -what- is failing.

Yea that's what I'm struggling with.

I can strip everything out of the top assembly one by one until I've isolated the issue, but I still can't get the mechanism to function, and I don't know what happened to cause the failure.

The model is definetly a mess. It is in-progress created from a lot of client iges parts, so working from the top-down would've been counter productive. I hoped there would be something obvious for mechanism modelling in Creo, like a set of best practices or something.

Would it make more sense to model the assy's/subs as trsaditional models (ie not mechanisms), and drive them with family tables or something?

Edit: And thanks for the link, Vladimir! I'll read through that thread carefully.

Re: Multiple sub-level mechanisms do not function in top level assembly

Antonius,

I fully understand your point, especially the "Is there not any kind of diagnostic tool within Creo that can help sort out these types of constraint errors? Model tree columns that will highlight the failure? "FIXIT" button?".

Unfortunately there is no such magic in Creo :-) ... since it is usually preferable not to take decision instead of the designer - too high responsibility, and too low chance that any algorithm sophisticated as it could be will fully understand designer intent.

Investigation tools are however there. Best example - Reference Viewer. Detection of circular references tool in particular. I wish we had same visualization level for bodies ...

What we do have is Mechanism Tree, model tree column "body" (that will report body # for each component), and errors (agree they are not too informative). Working with Tree Column "body" / dumping it time to time you can see if things change as you work, and back analyses what you changed that caused unwanted bodies change. e.g. you added 5 subassemblies to top assembly that have total 10 rigid bodies and start working in top assembly, and note that now you have 8 bodies. Means 3 bodies "locked" to one. The earlier you catch this - the easier to check what and how you constrained wrong.

Regarding tutorials - I do not pretend that referred post is sufficient. We need PTCU and learning connector much better cover Mechanism. I do make this point internally, but adding such a request at a technical committee could have even better effect.

Regards

- Vlad

Re: Multiple sub-level mechanisms do not function in top level assembly

Thanks again, Vladimir. Can you expand on how to report errors in the Model tree? I found the body # column, status, and dependency, but I do not see of a way to show errors in either the mdeol tree or the mechanism tree. The information reports also do not provide this.