Joints not keeping limits

[WillL84]

I have a simple pneumatic cylinder with a cylindrical joint with limits for the rod travel. As I'm working with the assembly the end limit keeps removing itself randomly. I have to edit the joint and re-check the checkbox for the end limit. This was also an issue back in Inventor 2023 and way back in 2015.

 

[johnsonshiue]

Hi Will,

You may want to right-click on the Joint -> check Protect. Depending on the Joint type, the angular limit may not be obeyed. It is because the overall degree of freedom could be impacted by the angular limit, leading to locked-up assembly.

Many thanks!

[JDMather]

@WillL84 

Have you tried Assembly Constraints in place of the Joints?

[WillL84]

@johnsonshiue The angular limits are not used, only the linear. It's the end limit that keeps unchecking itself. I tried using the slider but I can't figure out how to get it to work properly, it keeps wanting to make the piston/rod go sideways out from the body.

@JDMather I did not, I didn't know it was possible to add limits to standard constraints which is why I usually use joints for these kinds of things (linear actuators, pneumatic/hydraulic cylinder assemblies. How do I use limits with constraints?

[JDMather]

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@WillL84 wrote:

...(linear actuators, pneumatic/hydraulic cylinder assemblies. How do I use limits with constraints?

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Easy to do and I have never experienced any issue with Constraint Limits.

Attach example assembly here for demonstration.

[WillL84]

I've attached the assembly in question, thanks!

[JDMather · Accepted solution]

@WillL84 

The key is to click this chevron to expand the dialog box.

Now you should see the limits options that you are familiar with when using Joints.

[WillL84]

Thank you! TBH I never even noticed that icon down there!

[whinkle]

FWIW this issue has plagued me over many Inventor versions -- what seems to happen is that when there is a conflict between a joint's limits and some other constraint (warning message, 'sick' icon) and you 'continue', the joint limits get un-checked and the values erased.  Rather than just being ignored, that is.

Most annoyingly, this percolates down into joint limits within flexible subassemblies, and saved to file that way.  So such subassemblies subsequently are flapping around wildly until limits are manually re-edited into them (even if the subassemblies are common to other assemblies).