RE: [CAD_CAM_EDM_DRO] has anyone tried dynamic damping?

The D term in a PID controller acts as damping. This is a crude form of the
idea you present. More sophisticated solutions that would involve
micromanipulator (as the piezo you suggest) and a well understood system
have been done, but this is not exactly in the category of hobbyist
activites. There are quite a number of PhD dissertations on this very
subject. It is probably a bit beyond a Master's degree thesis, but you
might be able to take a stab at it given a couple years of study.

Then again, getting it to work once for a specific cut on a specific work
piece is one thing. Getting it to work on a regular basis for a variety of
cuts, thin wall work piece, thick castings, finish cuts, rough cuts, and all
the rest, is quite another matter all together.

G. Jackson

-----Original Message-----
From: Elliot Burke [mailto:elliot@...]
Sent: Friday, January 31, 2003 1:23 PM
To: CAD_CAM_EDM_DRO
Subject: [CAD_CAM_EDM_DRO] has anyone tried dynamic damping?

This is some thoughts about dynamic damping:
consider a machine as a damped mass and spring system, with a cutting tool
driving it with a periodic force. If mass, stiffness and damping are just
so the displacement at the point of the cutting tool will be low.
Unfortunately this requires a massive system for large forces and low
frequencies.
So, either make the tool go really fast (impractical in many cases), or
extract the vibrational energy from the system with a motor.
What I am proposing is to put a strain gage(s) between the work and the vise
or embedded in the work holder or the tool holder, then a few piezo electric
motors under the work or close to it. The dynamics of the machine should be
well characterized, a servo can be made to make the system at the frequency
and phase of the driving force much stiffer. The piezo motor could push on
a free mass, which would wiggle around a bit, the piezo would pull the
vibrational energy out. This piezo extracts the energy because the phase
between force and displacement is 180° reversed from the normal case.

Since the machine structure is well characterized, knowing the forces on it
would enable the low frequency deflections to be calculated as well. These
could be used to correct the deflections in software.

Would this be trivial? No. But it might be able to make rigid, lightweight
machines. Think of a sherline sized mill with the rigidity of a 2 ton mill.
Not only would the quality of cut be better but they should be more quiet.

In such a system perhaps the way bearings could be simpler as well.

Machine builders, what do you think?

regard-
Elliot B.


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