RE: [CAD_CAM_EDM_DRO] Gecko ERR/RES Handling

There is another way to look at the 8 bit position error
question. True there is +/- 128 counts either side. On a system using
a 250 CPR encoder with a 2/1 ratio timing belt and a 5 TPI lead/ball
screw you would have 250X4X2X5 or 10000 steps per inch. Each step would
be .0001" and if the max error was 128 you could have a .0128" max error
before faulting which for machining would likely be way out of spec.
Thus a +/- 128 count error would be unacceptable and you would want the
axis to fault out. Even worse are some servos that would accept 32 bit
error which would only increase the amount of error with the same
encoder. The trade off would be that you could run a much finer encoder
say 1000 CPR which would be 40000 steps per inch and a 256 count error
would only be .000025 X 256 which would be .0064" which would still be
unacceptable for machining. But then you would also need a faster pc to
run the program.
If your Gecko G320/G340 faults out to easily then there could be one of
several problems. The first is that the G320 need a signal that is
positive going. I recently tested Maxnc S&D and found that the Geckos
would fault very easily. So I loaded Desknc for Dos and set it up with
the signals also going negative(I may have this backwards but you'll get
the idea) and the Gecko G320 replicated what I saw with MAXnc. Then the
only thing I changed was the signal type from negative to positive in
Desknc. WHAT A DIFFERENCE!!! Whereas with Maxnc step and direction, I
really had a big acceleration ramp and could not get anywhere near the
speed that I wanted. With the change of signal I could shorten the
acceleration curve and get awesome speeds. So check your software. Let
me know what you are using and I might be able to tell if that is the
problem.
The other problem is not setting the acceleration curve properly. I was
messing with desknc for windows and cncpro on another day and ran into a
time consuming problem of setting the configuration files so that the
acceleration was quick yet would not fault out the geckos and still
maintain top speed.
Last you may have an inertia problem depending on the machine and you
may have to increase the ramping of the acceleration curve to over come
this.
But I suspect the problem lies with the software and not with the
Gecko's.
With regard to the err/res question I have a little PCB that I use on
some of my Gecko systems that give me a front panel display of the axis
that fault out. But you don't need them once you set up your machine
properly. You can follow Mariss's previous email that uses a momentary
switch and daisy chains the err/res terminals together and uses the
encoder + and - or operation. I have mine set up for lift to engage (the
motors), release to run position and lower the switch to disengage the
motors. If any axis fault out all axis fault out.
Hope this helps
Dan

-----Original Message-----
From: David Eldredge [mailto:techdave@...]
Sent: Monday, December 17, 2001 10:19 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Gecko ERR/RES Handling

My 2 cents here:

My Dad and I are not very pleased with the Gecko error/reset handling
either.

I think there should be a separate output for the fault signal, and one
for
the reset line. The fact that you have to build another whole circuit
board
to handle these conditions is not very good design, in my opinion.

I also do not like the 128 step limitation on the fault condition. In
my
little world of messing with this motion control machinery stuff, ( a
little world admittedly) the +_ 128 steps is marginal. I know Marris
says
it is plenty, but I remain unconvinced. It is a pain in the neck
getting
faults all the time while I am developing stuff, like my CNC plasma
cutter.

I think there is an alternative, and I have ordered some in to try, but
I
realize that this list has a lot of loyalty to Marris, (GECKO) and
recognize
that he has helped many folks and has taught us all a lot too, so I
offer
these 1cents worth of comments in hope that Marris would reconsider for
others who may feel the same.

Dave