Dynamic simulation of spherical mechanisms

[shashank.sharmaXY9H6]

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.

[WHolzwarth]

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

[shashank.sharmaXY9H6]

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

[shashank.sharmaXY9H6]

zip files

[shashank.sharmaXY9H6]

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

[JDMather · Accepted solution]

See Attached.

[JDMather]

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

[shashank.sharmaXY9H6]

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.

[JDMather]

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@shashank.sharmaXY9H6 wrote:

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

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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?

[shashank.sharmaXY9H6]

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/

[JDMather]

Thanks for the link.