Re: Re: Which Software?

>    From: "gadget_c <billsand@...>" <billsand@...>

<s> 

> > The size of this error register depend on the manufacturer of the
> > driver, on geckos is 128 steps I belive. If the error register gets
> > more steps than it can hold it will reset to zero this means all 128
> > steps in case of the gecko are lost.
> > 
> > So called real feedback software monitor the error registers
> > constantly and desides what action to take if the error exeeds
> > a certain value. (syncronisation of all axes)
> > 
> OK
> I'm with you with what you describe - a driver of much
> sophistication and superb development(I'm told). My concern is that
> the position is still lost as far as the software goes. Working with
> 3D and losing position along with breaking a tool will most
> certainly justify a restart from zero. My wish is that with servos,
> the correction or position is totally controlled by software with
> feedback from a directly coupled motor to the worktable. Why leave
> any part uncoupled? I'm still in the learning process. Should I have
> purchased a commercial NC milling machine? Am I asking too much of
> this 'hobby' machine?

This is a great explanation of error by torsten. The only thing missing
is that when the Gecko 3xx series exceeds 128 steps it faults and shuts
down the drive and motor. Now the operator should know that there is a
problem and that when cured, the machine will have to be homed again.

Even a commercial CNC milling machine has error size and buffers that
hold the difference between commanded and actual position. The
difference between the Gecko setup and a full servo feedback is that
Gecko's fault point is a fixed size buffer and it reports only to the
drive amp itself. A fault can be reported to the PC if the program has
provision for it.

With full servo feedback in the EMC, you can set that value as small as
you like. You can make it fixed size for all speeds or you can ramp it
up as speed increases. The ramp means that you allow more position error
during a rapid but pinch the error down as you approach final position.
During milling moves, the error can be very small.

This is the same math and logic as would be applied by many commercial
controls. Some commercial controls use two ramps with a settable speed
point between. Some use a non-linear error computation. For a small
part of the price difference between commercial and EMC, I'm sure that
you could pay someone to write the error routine any way that you liked
-- 'cause it's all open source.

Ray