Re: [CAD_CAM_EDM_DRO] Active damping

> You're right, of course. A cast ribbed table can be made quite flat.
> Unfortunately it isn't very stiff, and will deform under its own weight.
> When I speculated that a servo to kill vibration might be a good thing, I
> was referring to not only table vibration, but ways bouncing around,

columns

> flexing, spindles and bearings flopping around, screws winding up and
> unwinding, and so on.
>
> Elliot Burke

Yes a cast table is great. Big bucks though.

As this latest machine is all high q welded tubing I expect to get some
significant resonances. I did not have the computational horsepower to do
more than a static finite element model but I tried to use some common sense
at least.

However I have worked a good bit with active damping. I will try to tame any
bad resonances I find with tuned passive absorbers but if needed I will use
active damping. The spindle
is at the end of a variable length cantelever and will have a changing
resonant mode depending on z position. Perhaps I won't have to do anything
but if it needs an active seismic mass near the spindle I can do that. I can
tune a digital filter
to make a mass behave as a virtual larger mass, spring,
or dashpot just like a motor. A z axis position variable spring
is also workable to make a semi passive absorber track
shifting resonance. This has phase margin advantages because it is a form of
feedforward.

I may try a tube in tube construction on the next one with
urethane or polymer concrete poured in the interstitial spaces.
Some good work has been done on this and it makes a welded steel structure
that is very well damped but still light-
the steel tubing is still mostly air inside.

Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.rabun.net/~leswatts/wattsfurniturewp.html