Dynamic Simulation for Kinematic analysis of linkage

[Loremaster72]

Greetings.  I'm new to dynamic simulation and am having trouble running a simple kinematic analysis on a linkage.  I'm trying to determine the vertical force on the end of an excavator boom throughout its range of motion, as generated by the boom cylinders.  I have been studying the tutorials and have skimmed through Wasim Younis' book on dynamic simulation.  In my case, I have a simplified model prepared and moving correctly.  I have fixed the redundant constraints.  I know what angle the boom will move through, and what the maximum force on the cylinder piston is.  I have been driving the boom by controlling the angle of the boom, and it moves correctly when I run the simulation.  I have tried a couple of techniques for applying the force to the cylinders, once as an external force, once as a force on the constraint between the rod and barrel of the cylinders.  Unfortunately, I can't find a way to probe force at the end of the boom as it moves through its range.  I even applied a spatial constraint between the base frame and the tip to try to querry, but all I get is a 0 force at the boom tip.  I have to be missing something simple.  Can someone please point me in the right direction?

[JDMather]

Attach your assembly here.

[Loremaster72]

I was really hoping to not have to post the files here, as normally I am not allowed to share design data outside the company.  In this case, i think it is non-specific enough that I could.  The pack and go was too large to post, so I deleted the Design Data, Templates, and Old Versions.  The assembly, Excavator Upper Assy.iam, is in Inventor 2013.  I'm working with the rep "Boom Only" for now.

[JDMather]

I only had time for a quick look - so this is only to get you started, and might start you down the wrong road.

Create a Workpoint and Axis at location you want to know Unknown Force.   (in the part ipt file)

Remove the Imposed Motion from Revolution1 joint - we will drive that when calculating the Unknown Force.

Make sure you set to Revolution1 joint in the dialog box.

Verify that we are in the right ballpark.

I did not take time to carefully think this through and make any close examination - so I leave that up to you.

[Loremaster72]

Well, I think we are getting close.  I removed the imposed motion and added the unknown force for Revolution 1 as you indicated, but am getting completely different results than you.  My force comes out as 0 across the band, not the curve you are getting.  I wonder what I'm doing wrong?  Qualitatively, your curve looks about like what I expected.  I will probably be concentrating on the Y-component (vertical) of the resultant force.

A couple of other things I noticed.  The range should have been 14 deg through 108 deg, a net 94 degree range.  Also, the force on one of the hoist cylinders was not turned on.  Neither of these change my output. 

[JDMather]

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@Loremaster72 wrote:

1. My force comes out as 0 across the band, not the curve you are getting. ..

 2. The range should have been 14 deg through 108 deg, a net 94 degree range. 

3.  Also, the force on one of the hoist cylinders was not turned on.  Neither of these change my output. 

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1. I am using later release - you will have to reattach your assembly file here with your new settings. I did clear the all traces in the Output Grapher except for the Unkown Force.

2. Easy to change.

3. I checked again - with both disabled and both enabled.  Gave me an idea of what is actually being measured.

Attach your revised iam here.

[Loremaster72]

Well, I found a machine that had 2014 installed on it, and tried the model again.  I also re-created one of the prismatic joints to make sure that they were both configured to act in the same direction.  I'm still not getting any force outputs.  Attached is the adjusted model from version 2014.

[JDMather]

In the latest assembly - you didn't set the Direction as I would expect?

[Loremaster72]

Thank you!  That fixed it!  One last question for you:  The unknown force generates a combined total "Force" and three directional components.  I thought that these were based on the Global coordinate system, but this last change seems to indicate to me that they are based on the orientation of the selected point, and that the orientation is relative.  Which interpretation is correct?  If the latter, is there a way to determine the force relative to the global coordinate system orientation?  I might have to add a component to the pin hole that rotates to keep a plane horizontal/vertical, and put my querry on that.  Determining a globally vertical force is the goal I have for this analysis.

[JDMather · Accepted solution]

Well if you have a vertical axis to initially select - simply switch to Fixed Load Direction rather than Associative Load Direction.