User defined units

[Soori]

Hi all,
I am working on modal analysis of gyroscope. The dimensions of the gyro are of micron level. Can anyone help me how to set the units to microns.


Thank you
Soori

 

[pat59]

I am afraid you will have problems to define micron as length unit in I-DEAS. The important question is : what do you want to do ? Geometry modeling ? Simulation ?

The default global tolerance in I-DEAS is 0.01 mm or 10 microns ! If you wish to create dimensions of micron level you need to set it to 0.0001 mm which is the smallest value allowed (/MO SPE T DF...). And then, you will only be able to define 1 digit on your dimensions !

My feeling (and my experience) is that it is not a good practice since you may hit numerous problems working with a non standard tolerance value. Maybe the latest versions are more robust on that side. Other people may have experience in doing that ???

If possible, I would suggest to use a virtual and scaled model. Replace micron by mm on your dimensions, use mN for force unit. Then, you just have to scale your material properties to make everything consistent...

Hope this helps.

 

[Soori]

Hi Pat,
Thank you very much for your reply. I am a beginner in using FEA package(I-DEAS). I havent understood some of the points in your reply. I will state them one by one. I have to do find out the natural frequency of MEMS(MicroElectro Mechanical Systems) gyroscope. The gyroscope is a plate with a diameter of 2000 micron and thickness of 45 micron. The material is silicon.
I have some more questions. How to set the global tolerance in I-DEAS to 0.0001mm? And even after I set it to that tolerance level is it possible to define 2000 microns, as you said that we can define only 1 digit of dimension. And I have tried using the user defined units from the preferences menu, and I am facing many problems during the Master Modeling part. Is it possible to define units that way(from the preferences->user defined units). I am using I-DEAS 9 version.
The method you have suggested looks helpful. So if I change the material properties which are compatible with the microns it will give the correct natural frequency, right?

Thank you
Soori

 

[Soori]

Hi Pat,
I am awaiting you reply.

Soori

 

[Soori]

Hi Pat,
I am awaiting your reply.

Soori

 

[varmaNV]

hi soori
u r supposed to use 45 and 2000 microns. then why r u worrying to set units and all. this 45 microns is nothing but 0.045 mm. u directly use this values until otherwise ur value falls below 10 microns.hope it is helpful for u.
and still if u need to modify the accuracy
u turn menus on (ctrl+m)
modify -> special techs -> tolerance -> default tolerance
then change what ever u need. but it is not preferable.
let me know if u have any queries

 

[Soori]

Hi varmaNV,
Thank you very much. I was confused intially. I will try working on it and will ask u if I face any more problems.

Soori