topic Dynamic simulation of spherical mechanisms in Inventor Forum

Dynamic simulation of spherical mechanisms

shashank.sharmaXY9H6 — Thu, 18 Apr 2019 07:53:29 GMT

Hey all. I'm trying to simulate a four bar spherical linkage. It is working alright in the assembly mode i.e. dragging the links moves the mechanism in predictable ways. However, when I go to the Dynamic simulation environment, the mechanism is always overconstrained. I'm at a loss on how to apply all the constraints so that it animates. I've tried revolute joint, spherical joint, point-line joint, etc but unsuccessful. Can some please guide me? Thanks.

Betreff: Dynamic simulation of spherical mechanisms

WHolzwarth — Thu, 18 Apr 2019 10:05:55 GMT

IAM is not enough, attach your IPTs, too. Best way is zipping them all into one file.

Betreff: Dynamic simulation of spherical mechanisms

shashank.sharmaXY9H6 — Thu, 18 Apr 2019 13:06:41 GMT

Hey! I've included the .ipt and .iam together in a zip file. Please have a look.

Betreff: Dynamic simulation of spherical mechanisms

shashank.sharmaXY9H6 — Thu, 18 Apr 2019 13:09:25 GMT

zip files

Re: Dynamic simulation of spherical mechanisms

shashank.sharmaXY9H6 — Wed, 24 Apr 2019 07:40:20 GMT

Still haven't found a solution. Anyone has any ideas?

Re: Dynamic simulation of spherical mechanisms

JDMather — Wed, 24 Apr 2019 11:58:28 GMT

See Attached.

Re: Dynamic simulation of spherical mechanisms

JDMather — Mon, 29 Apr 2019 10:43:57 GMT

Where did you go? I was going to recommend you for a job opportunity.

Re: Dynamic simulation of spherical mechanisms

shashank.sharmaXY9H6 — Thu, 08 Aug 2019 00:21:55 GMT

Hey JDMather,

Your solution works perfectly. Its really interesting how you constrained each degree-of-freedom to fully constrain a spherical mechanism even though its actually an over-constrained spatial mechanism according to Chebychev–Grübler–Kutzbach criterion. Thank You! Do let me know about the opportunity you had in mind.

For others who might be interested in simulating a spherical four-bar, use the following mating/constraining strategy:

(Assuming fixed base link)

Constraint 1: Spherical constraint between base and input link. (-3 mobility for input link)

Constraint 2: (Fixed Pivot 1) point-axis constraint between base and input link. (-2 mobility for input link)

Constraint 3: Spherical constraint between base and output link. (-3 for output link)

Constraint 4: (Fixed Pivot 2) point-axis constraint between base and output link. (-2 mobility for output link)

Constraint 5: (Moving Pivot 1) axis-axis constraint between input and coupler link. (-4 mobility for coupler)

Constraint 6: (Moving Pivot 2) point-point constraint between output and coupler link. (-2 mobility for coupler, -1 for output link)

If it doesn't work out the first time focus on the last constraint. Don't imposing spherical constraint between base-coupler link because it will make the mechanism over-constrained.

Re: Dynamic simulation of spherical mechanisms

JDMather — Thu, 08 Aug 2019 11:43:21 GMT

@shashank.sharmaXY9H6 wrote:

Do let me know about the opportunity you had in mind.

The position has been filled a couple of weeks ago.

This looks like an interesting mechanism - you have a picture of the full real-world mechanism that you can share? What is the purpose of the mechanism?

Re: Dynamic simulation of spherical mechanisms

shashank.sharmaXY9H6 — Thu, 08 Aug 2019 18:22:32 GMT

I'm exploring the use of spherical mechanisms in my research. They can have considerable application in origami-based folding mechanisms. Here's an article on using spherical mechanism to model a scissor door. Check it out.

https://mechanicaldesign101.com/2013/01/26/spherical-watt-i-six-bar-linkage/

Re: Dynamic simulation of spherical mechanisms

JDMather — Thu, 08 Aug 2019 18:38:19 GMT

Thanks for the link.