Re: [CAD_CAM_EDM_DRO] Re: Open (i think) design for a parallel robot (reprap ma

Jon,

The large-scale calibration is fairly well covered by the simulated
annealing method of estimating the systematic error parameters. This
discussion grew out of concerns about quantization, and (I speculate)
that quantization will cause a surface roughness on nearly any
surface machined with a hexapod.

The quantization-roughness may be far less than the roughness that
comes from servo control system errors, vibration, chatter, or other effects.

Have you been looking at EMC for hexapod controls? Do you know if it
can generate the transformed actuator commands, independent of the
real-time actuator controls? I don't have a G-code interpreter as
part of my system, which certainly limits how easily I can import
files from other people. Also, if EMC handled the dynamics of
acceleration and setting the cut rate, it would simplify the job ahead of me.

I'm wondering if I should try using spindle load (as measured by the
current consumption or some other means) as a moderator on cutting
speed, or is the key just keeping the tool and work cool and flushing
the chips well.

There is so much about actually machining that I need to learn.

-- Carl


At 12:38 PM 9/5/2006, you wrote:

>Carl Mikkelsen wrote:
>
> >A decent parabola would require a rather large billet to start with, and a
> >lot of material to be removed. I agree that it would be a good test.
> >
> >The proposed test came out of a discussion of quantization error, which
> >intrinsically prevents a hexapod from cutting a smooth plane, unlike a
> >Cartesian machine which could cut a perfect plane.
> >
> >What I was curious about is how to measure the small-scale deviations from
> >the desired shape. Isn't this property called surface roughness? What is
> >a simple way to measure surface roughness?
> >
> >
> >
>There are instruments that do this, surface roughness indicators.
>
>But, one other way is to do this backwards. Maybe the plane is the
>easiest, here.
>You mount a dial test indicator in the spindle, lock the spindle and
>sweep the indicator
>across the surface by CNC control. The deviation of the indicator tells
>the error.
>Sweeping an indicator across a granite surface plate would sure tell you
>whether the
>machine could move in a straight line.
>
>To bring it up to multiple axes, you could obtain a new bearing ball of
>the largest size
>possible, like maybe 2 or 3" diameter, and sweep the indicator around
>that surface. You'd
>need to make a heavy "nest" to hold the ball so it doesn't move.
>
>Jon
>

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