April 24, 2019, 10:15:34 PM
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 Can someone please walk me through how to calculate the payload inertia?

Author Topic:  Can someone please walk me through how to calculate the payload inertia?  (Read 1076 times)

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August 21, 2018, 02:03:25 PM
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dohlfhauldhagen


Greetings all. I have been doing robotics and simulations for a few years now, and something that no one in my field ever seems to know how to do is calculate the payload inertia. I have the Fanuc Excel sheet where you can enter in the mass, inertia, and the center of gravity of your robot tool. Whenever our design agency gives us their 3D models from Solid Works, they only give us the mass and the location of the center of gravity. If I inquire about the moments of inertia, no one ever seems to know what I'm talking about or how to calculate it. So I always just kind of let it slide and just hope that the tool will work out based on just what I've seen work in the past. I've tried googling and looking through the manuals, but I can never really find anything that explicitly tells me how to do this, and I really would love to know how so that I can do my job better and more accurately! So does anyone have anything that I could reference that would help out in this regard? Is this something that Solid Works is supposed to calculate for me? I appreciate any info that anyone can shed on this topic!

Today at 10:15:34 PM
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August 21, 2018, 02:13:14 PM
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ROBOENG_1


SolidWorks measure tool should show your moment of inertia

August 21, 2018, 02:35:09 PM
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Nation


In solid works, you have to setup a coordinate system to match the faceplate coordinate system, then output the COG and the moments of inertia about the COG in that coordinate system. You only need the principal axis, boxed in red in the attached image. You also need to convert solid work's output from grams*mm2 to kg*m2.

If you want to do it by hand, the HandlingTool manual goes over how to calculate moments of inertia in the payload section.
« Last Edit: August 22, 2018, 12:43:19 PM by Nation »
Check out the position converter I wrote here!

August 21, 2018, 06:42:12 PM
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dohlfhauldhagen


2[/sup] to kg*m2.

If you want to do it by hand, the HandlingTool manual goes over how to calculate moments of inertia in the payload section.

Thank you so much! I will definitely forward this to my design guys. Cheers.

August 22, 2018, 11:55:29 AM
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TygerDawg


Isn't there something more?

If the SW model has all of the mass density data input correctly for each component, then a mass of each component can be calculated by SW.

But is isn't it necessary to develop TWO mass moment of inertia calculations?  The first corresponds to the Joint6 tool flange rotation axis.  The second must be about the Joint5 wrist rotation axis (not at the tool flange).

Get those two numbers, compare against published data.  If the EOAT MMI data is less than the published limits, then the robot can move the EOAT in all configurations at all speeds and maintain the repeatability specs.  If greater, then speeds must be reduced (generally).  This takes care of dynamic torque about Jt5 & Jt6.

Finally, for a rigorous analysis, one must also look at worst-case static torque about Jt5 & Jt6.  This would be gravity loads + other estimated force loads about those axes.  Calculate, and compare against specifications.
TygerDawg
Blue Technik
Virtuoso Robotics Engineering
www.bluetechnik.com

August 22, 2018, 12:49:40 PM
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HawkME


If you follow Nations method then that is all you need. Entering those values into Payload Checker, RoboGuide, or the Robot itself will tell you if the robot can handle it. Payload checker takes into consideration all of the wrist joints so you shouldn't have to do any more analysis.

August 22, 2018, 12:50:52 PM
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Nation




Please note that I updated my attached solidworks output image. I had accidentally boxed the wrong inertias.

Today at 10:15:34 PM
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February 08, 2019, 09:35:08 PM
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Ravi Bhatta


what is wrong with what you have boxed? I think it is the same inertia Lxx, Lyy, Lzz that robot payload calculators ask

February 08, 2019, 10:00:53 PM
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Nation


Nothing. It is correct now.

As of August 21st, I had the wrong items boxed. I noticed this on August 22nd, and updated my post with the correct image.


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