topic Re: Dynamic Simulation Manual Joints in Inventor Forum

Dynamic Simulation Manual Joints

swalton — Fri, 15 May 2020 14:44:55 GMT

I am exploring Dynamic Simulation for a project at work.

I can't seem to get a revolution joint to behave as expected. How do I control which component in the joint rotates vs which component is stationary?

In my case I have a rotor (built as a sub-assembly .iam file) and two bearing block ipts. The bearing blocks are fully constrained in the assembly. The rotor is constrained with an axial mate and a flush to one of the bearing blocks.

If I use the Automatic Joint Conversion, IV joins the rotor and the two blocks as a welded group. If I use manual conversion, I get a revolution joint, but the bearing block rotates around the rotor. If I create a revolution joint, the bearing block rotates about the rotor.

I've attached a pack-n-go for review.

Re: Dynamic Simulation Manual Joints

JDMather — Fri, 15 May 2020 16:44:09 GMT

Inventor is trying to help you by removing degrees of freedom - (think Lug Nuts on a Wheel) and in this case you want the rotation.

Ground the bearing blocks in the assembly.

Go back to DS and turn automatic Joints back on.

In the Grounded group, right click on the sub-assembly and select Retain DOF (retain Degrees of Freedom).

Re: Dynamic Simulation Manual Joints

swalton — Fri, 15 May 2020 18:21:11 GMT

Thanks.

That seems to work. I'd never notice that command in the menu before. I thought that Inventor was supposed to automatically convert the constraints to joints.

Does this mean that I can actually fully constrain components in the assembly, but then release/retain DOF in the simulation? I've always thought I had to leave components underconstrained so I didn't get unneeded joints.

Is there a way to enable/disable a joint as a function of simulation time? For example, the planer joint works fine for block sliding on an inclined plane. Once the block reaches the end of the plane, I would expect it to fall in the gravity direction. The only way I've made that work so far is to use a 3d contact joint between the block and the plane. This runs slow.

Re: Dynamic Simulation Manual Joints

JDMather — Sat, 16 May 2020 12:10:54 GMT

Play the attached DS simulation.

Re: Dynamic Simulation Manual Joints

JDMather — Sat, 16 May 2020 12:43:07 GMT

@swalton wrote:

Is there a way to enable/disable a joint as a function of simulation time?

You can set timing via Input Grapher.

Re: Dynamic Simulation Manual Joints

swalton — Sat, 16 May 2020 14:06:19 GMT

Thanks for taking a look at my dataset.

As I suspected, I had a number of miss-conceptions about how Dynamic Simulation works.

1. I thought that 2d contact needed a dedicated sketch on each part. Not only that, but the sketches had to be co-planer. Your example shows that I can use the outline of a component to set up this joint. This makes that joint easier to use.

1a. Are 2d contact reference surfaces/sketches required to be parallel throughout the entire simulation?

2. Is it possible to use the top-level assembly origin geometry in joints? I can pick component origin geometry in the browser, but I can't pick the assembly geometry. Seems like a weird limitation.

3. I don't understand how to suppress a joint at specific time in the simulation. For example, the Planar:1 joint keeps the moving plate centered on the Y-Z plane. Once the plate has passed the rotor, I will have other components that will force the plate in the positive X direction. Planar:1 keeps the plate orthogonal to the assembly origin, but the real-world motion will be different.

I'll keep experimenting with various combinations of joints to see if I can get the motion I want.

Re: Dynamic Simulation Manual Joints

j.palmeL29YX — Sat, 30 May 2020 17:37:25 GMT

@swalton wrote:

ATU00-30011 updated 9 am.zip

Refering to your updated data set I did some small modifications.

After adding 3D-contacts I get results (example) as shown in this videos.

>>Real time<<

>>Slow motion 1:2<<

>>Slow motion 1:2 other view<<

(The result of the Dynamic Simulation was visualized with Inventor Studio).

But I doubt that you get realistic results. Small modifications at the simulation parameters lead to very ifferent results. I think it's only for fun.

My data set (IV 2021) attached.