Anthony
Absolutely beautiful, great work.
I've done something smilar, but not as spectacular.
Unloading has never worked for me (the automatic way). Same message as you got.
I use an excel sheet that generates cam profiles. I always set the amplitude to one (1) and use the result as a scale factor for my load or prescribed displacement. That way I also scale it back to zero again.
My third picture shows a graph of 2 such curves (The blue one preloads the rubber block in my example, the red one drives the punch)..
It works!
Erik
And yes , maybe we start a new subject on non-linear analysis in general. I made several really cool examples... I'm a great fan, hope they keep developing the capability.