Showing motion has been a challenge....Those that are familiar with solidworks probably know configurations and using constraints to demenstrate positions of cylinders and such. From what I can understand there are what seems to be the equivalant of advanced constraints that allow motion. My issue is for whatever reason it seems like certain constaints or patterns of components fully constrain my model. Things that I guess I am use to using in solidworks and inventor that would not. The other issue I am having is for whatever reason my subassembies seem to allow me to click and drag cylinders. Then the next day or next time I reopen them they do not. This is extremely frusturating.
We are using creo 4
Solved! Go to Solution.
Two things that typically cause the model to "lock up":
Not sure why cylinders stop moving the next time you open them.
I have the allowing assumptions unchecked.
I have noticed mating to multiple parts are causing issues whether it locks up or behaves not completely constrained. I've been constraining to the datum planes now. Other features I'm noticing that's causing this is using patterns of components.
Is this fixed in the newer versions of Creo? I can't believe how inefficient this program is.
Well, one will be usually inefficient when using an unknown tool. You'll get good support from this forum because Creo is not easy to "get to know" all by yourself.
I recall that in Solidworks, one easily specifies the constraints (mates?) between components and it "finds" the kinematic configuration of the assembly. Well, this is not how things work in Creo, and you have to be very explicit when creating kinematic connections. What's more frustrating is that they system does not give you good tools to fix the problem.
Actually, I still don't quite understand how it all works - I took the cylinder example provided elsewhere in this thread and tried to make it lock up by having the rod's constraints be "shared" between different models, but it still works. I include it to touch on the "regeneration value" aspect of a kinematic connection - maybe those are responsible for your cylinders "resetting" themselves.
BTW, note that you can hold CTRL+ALT and then left click on a component to drag it around subject to its constraints. Also, I assume you know how to use the "Drag Components and Mechanism snapshots" tool to capture different motion states so that you can then show them on your drawing (as different explode states - yeah, kind of a hack).
Motion can be a little tough to get the hang of in Creo but there are some tips that can help make the learning curve less steep. Here are a few:
I've attached a very simple reference assembly for you to look at (Creo 4.0). Notice that I have moving and non-moving separated, self-contained, and referencing a common skeleton. The cylinder spans both (body can't move but rod needs to). In this case, I use two constraint sets. One to position the cylinder in the assembly and another to link the rod to the moving body. The cylinder itself needs to be mechanized to do this so take a look at how that is set up as well.
There are a bunch of different ways to do this but we teach two basic schools of thought:
The second option is preferred in my opinion because the mechanism constraints are stored at the upper assembly level and will allow you to reuse the cylinder anywhere you want. Especially if you have different working strokes for each application of a cylinder. If you use the same datum setup or skeleton, I think this method is the easier of the two.
We have both Creo and SolidWorks running in Windchill. The rules that we follow for motion vary slightly due to software differences but are pretty much CAD-agnostic.
I hope this helps!
Ok so here is a good example of what I'm talking about. I have this gripper, using the slider (I believe) constraint system. The Coincident and angular offset are both planes of the gripper finger to the planes of the first component. I do this with both fingers. I use the gear mechanisms to synchronize movement. Works perfectly as just an assembly. I throw it into my main assembly and they loose synchronization.
Without seeing your model up close, i can't tell what went wrong. There can be so many things with this software.
One thing I can comment is I don't use general constraints if a simpler one can work. For your case, if your gripper fingers are sliding, why not use sliding joints?
I include the CREO4 example with a gripper.
How are you constraining the gripper in the upper level? You can't constrain the gripper assembly via the gripper fingers if they are mechanized. Your motion would get locked down.
This is the gripper. I ended up supressing the attached fingers, deleting all the constraints but a fixed constraint and am still having this issue. It will work fine as an assembly, it only has issues when its a sub assembly in my top level.
I assembled your gripper assembly into a new assembly and the mechanism still functions. This leads me to believe that the issue is being caused by the way the gripper is assembled or the way other things are assembled to the gripper. The gripper fingers seem like a good place to start looking. If they are assembled to the gripper assembly but cut to part data (the thing getting gripped) this would lead to issues with the mechanism. Try isolating the gripper in the upper level. Another thing to look at is whether or not the upper level is mechanized in another level up. If that's the case, you might want to switch the gripper placement constraint set to rigid in its upper level.
Thanks for sharing - I was not familiar with the way you made the gear connection there. You see how in my example I had a dummy link.
Anyway, my notes:
when I placed your gripper into the motion_example in this thread, then the gripper did move, but in a very strange way. Basically, the 1:1 ratio was lost and one gripper would move very slowly compared to the other.
then I noticed that the gripper is in mm, while the motion_example assembly is in inches. I switched motion example to be in mm and the proper motion was restored.
Interesting that my dummy-linked version can be set to inches and still works...
So I'm thinking that there is some funny business with units going on. Definitely not an unheard-of-issue in Creo modeling.
How is the unit consistency in your actual models?
You could definitely be on to something. Looking at the file history of the gripper, it looks like native CAD was downloaded from the supplier's site. We discourage this and tell our users to download neutral files. The native models likely came in as millimeters.