This is my first independent attempt at a dynamic mechanism analysis.
I have four horizontal sliders on a slide base that has a dove tail groove down the middle.
The sliders have a rectangular shape, with straight plane faces, and are all 100 mm wide.
The first slider is a servo motor, start position 0 and the end position is 900.
Sliders 2, 3, 4 have start positions 200, 400 and 600 respectively, and end position 900.
Distance between sliders is 100 mm.
I have set Collision Detection to Global Detection and to Push Objects upon collision.
My starting problem was establishing the proper 3D Contacts between the four sliders, and I made a mess of it in the end.
Out of sheer desperation I added masses to all sliders (picked steel in the end, as I had a lot of problems with brass, for unknown reasons) and I fumbled with Damping = 80, Young’s modulus = 2e6 to 5e6 and Poisson = 0.30 (without really understanding how these really work).
This is one of the error messages from that stage:
"The properties for material PTC_SYSTEM_MTRL_PROPS are wrong. Please select other material or use user defined values."
Hence brass, then steel.
It became evident that trying to select two plane surfaces will definitely not work, and then I found out that CREO does not allow that (??) and I had to use a SWARM of datum POINTS as a subterfuge (one of the ones mentioned by Gemini).
I added a swarm of points to all sliders, but I am not sure that they are used in any way, shape or form.
For the 3D Contact I was able to create some sort of sphere close to the intersection of two edges on the corresponding faces of the sliders, but even those proved difficult.
After adding the fourth slider the analysis would just stop, I was getting "all positions constraints cannot be simultaneously satisfied. the following position constraints can't be satisfied: 1) sphere to plane 3d constraint can't be satisfied in model contact 3".
I played with the dimension of that sphere, nothing worked.
At some point I found out that you can have more than one 3D Contact point between two faces, so I added one more to see if it makes it better for Slider 4 -- it did, I was able to run the Mechanism Analysis to the end and produce the video clip, but I still have some problems, and I would still like to learn how all this works.
First problem is the gap between the moving servo motor slider and the rest of the sliders (it is not supposed to be there) and the stuttering of the servo motor -- every time it collides with something it stops and needs some time to restart the whole movement.
If I could make the gap smaller (no need to get rid of it completely if that is not possible) and make the stuttering less evident (cut it in half) I could live with that, but the second problem is a show stopper -- I need to prevent the last slider taking off on its own, like a cannon ball, after the collision with Slider 3.
I had the same problem at the beginning with all the sliders, but after I tinkered with the mass and coefficients and the swarm of bees, the problem disappeared somehow.
Nevertheless, I was not able to replicate that tame behavior with Slider 4, because I did not know what I did well in the first place with the other sliders.
In the end I also got a warning that the mechanism cannot be assembled anymore...
If someone knows how to straighten all this out, please give me some pointers!
I have shared the parts and assembly in the ZIP file, no idea if that is allowed, please let me know if I have done something wrong.
Many thanks!
