Has anyone experienced unstable servo operation due to high load/motor inertia ratios?

I've found several articles on the subject, the best one being:
http://www.motionvillage.com/welcome_center/articles/Inertia.PDF

Just wondering if anyone has had some practical issues with this in their past designs?



Chris

Chris, What symtoms are you getting, usually wrong inertia match shows up when you want to move an axis in rapid and a servo goes into overload, or a stepper will stall, there are quite a few programs where you can plug in your numbers and find out, the magic number is usually to keep the motor to load inertia ratio lower than 10:1 . the answer of course is to apply a reduction of some sort, fortunately the ratio is reduced by a squared of the reduction.
Al

The machine is not complete. I was just deciding if I should use a belt drive reduction or not to avoid a potential problem.

The servo's I have are of sufficent torque without reduction.

I was using Danaher's Motioneering software and if the input's are correct I'm running at about 7.5:1 with the servo's I have.

The table is very very heavy ~1500lbs but quite rigid.

Before using the software I was not even aware of matching inertias.
I was just wondering if this was really significant or more of a theoretical rambling :)

Thanks
Chris

Chris, If you want to achieve a certain rapid feed acceleration rate, it is well worth designing for it, I made the mistake a long time ago of winging it and regretted it, I usually shoot for 5:1 now to be on the safe side, and that gives a better margin in case of oversight or the desire to push the acceleration a bit more.
Al

Thanks!

I've put alot of time, money, & sweat into this machine so I should not skimp on the belt/pulley now.

I just don't have alot of room for a pulley.

BTW, do you use Danaher's Motioneering software?
If so do you know what the difference between "slide weight" & "carried axis weight"?
Also what do you think the GIB force of a 30mm THK is? Or does it even have one?

Chris

Chris, I have used Motioneering, its not bad. as far as I know the slide weight is the weight of a particular axis and the carried axis weight is the the weight of an axis when carried by another axis, this would be like a gantry table where the y axis is also carrying the x and z axis.
Its a bit like a CNC mill where they ask for the table weight and the max weight carried by the table.
it seems a bit convoluted.
Al