Error in Mechanism Cam Motion

[slingblade]

I have modeled my cam and pawl for a ratchet but when I run a Mechanism Analysis I get errors.<?:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" />


The analysis will run for a short time showing the correct operation of the mechanism but then randomly stop with:


"Dynamics analysis failed at time X.XXXX"


"AnalysisDefinitionXX failed."


The failures are never at a predictable time and sometimes the analysis will nearly complete.


I have a torsion spring forcing the pawl to contact the ratchet wheel and a cam connection with lift off enabled between the pawl and ratchet. Damping and spring constants don't seem to have an effect.





When the analysis fails the parts seem to be interfering as shown in the attached JPG.


I can run analyses in Mechanica and everything seems fine.


Any ideas why I am getting these errors?

 

[Kaz Z06]

slingblade,


It is difficult to undersatnd your problme from the staic image. Is it possible to share the files with us (ideal), or at least a movie of what did solve? All I can tell you is that the curves for each cam have become overlapping, which will not allow the model to solve from here.

 

[surajram]

Hi slingblade,


Try one of this..


1. Run the analysis keeping frame rate as very high (pf the order of 100000).


2. Create a surface on ratchet & Pawl's outer surfaces and then define the cam connection.


Gud luck

 

[slingblade]

Thanks for the help. Eventually got it to work by making the two pawls and axle rigid then adding damping along with the torsion spring applied to the axle. I started with very high damping values and backing off until the motion was realistic.





Seems like mechanica can't deal with the sudden movement of the pawls and lets the pawl and ratchet gear collide.


A high frame rate would probably have hadthe same effect.