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T
TedG1-Visitor
1-Visitor
July 6, 2010
Question

How to calculate mass of assembly with mixed units

  • July 6, 2010
  • 3 replies
  • 5205 views

When I calculate the mass properties for my assembly I get an incorrect mass. I've traced the problem back to the fact that everything is in the default Pro/E units (in lbm sec) except one purchased component where the system of units is (mm kg sec). Pro/E is rolling up this assembly's total mass using the component's mass value in kg as if it's lbm.

How do I correct this behavior? Thanks.


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3 replies

D
DavidButz1-Visitor
1-Visitor
July 6, 2010

Change the units in the problem part.

T
TedG1-VisitorAuthor
1-Visitor
July 6, 2010

Yes, that's one way to solve the problem. But here's why that's not a preferred solution:

  1. Some of our purchased parts are specified by the manufacturer in English units & some in Metric. It's preferable to leave the parts in the units the model is created in so that they can be more readily checked for accuracy at a later date.
  2. Some assemblies the part is used in may be in English units & some may be in Metric. So changing the units of the part to match those of the assembly doesn't work in these cases.

Am I missing something? Pro/E knows the system of units the part & assembly are in. It knows the conversion factors between units. Surely it can be made to do the conversion itself when calculating the mass properties of assemblies with mixed units?

Thanks.

K
Kevin1-Visitor
1-Visitor
July 6, 2010

Another thing to check is to see if alternate mass properties have been assigned to the part. One thing that will happen is the mass of the assembly will be calculated in the assembly units but the mass displayed and used for the part in the assembly list will be incorrect. If you are using PRO_MP_MASS it will display the value using the alternate mass properties.

T
TedG1-VisitorAuthor
1-Visitor
November 18, 2010

It turned out the error was only visible when looking at the mass properties in Intralink. The values were all correct in Pro/E. I regenerated the Pro/E model, checked it in to Intralink Commonspace, & now the values are correct both places.

Thanks for the suggestions.

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