Re: Gecko ERR/RES Handling

Hi,

There are several issues here:

(1) SINK OR SOURCE?

It is much better to use common +5VDC because of the asymetrical
drive capability of logic circuits. They do a much better job of
sinking current (load connected from +5VDC to the output) than they
do sourcing current (load connected from the output to ground). The
difference can be more than 4:1. If you are going to source current,
use a 'scope to check if the output line swings from <0.5V to >4.5V.
You can use a voltmeter and toggle the "direction" output if you
don't have a "scope.

If you see less than 3.5V for a "high" output, then noise margins are
being comprimised and you may get ragged operation.

(2) PULSE POLARITY?

Pulse polarity (pulse is mostly high vs. pulse is mostly low) is not
an issue unless you come up against published timing limitations. The
opto-isolators use photo transistors, so the are highly asymetrical
in their minimum on and off times. This is due to saturated storage
delay time effects. The minimum "on" time is 0.5 uS while the
minimum "off" time is 3.5 uS. For example, if you are using a 2 uS
step pulse width, then the drive will not work if the polarity
is "mostly on", yet work perfectly if you switch the polarity
to "mostly off".

NOTE: "Mostly on" or "mostly off" refers to the opto LED current.
That would be a narrow "1" pulse with a "common = +5V" and a
narrow "0" pulse for "common = GND".

(3) MAXIMUM SPEED:

A DC servomotor has zero torque at its no-load speed. That is why it
is called "no-load speed". It cannot do any work because its output
power is zero (speed X torque = 0).

At around 85% of no-load speed the motor can provide its maximum
continuous torque. Use this value for maximum continuous output.

At 50% of its no-load speed the motor can provide its maximum power
(speed X torque = peak). This will be a torque equal to 1/2 of its
stall torque. This torque will also be 3 to 5 times greater than max
continuous, so use it sparingly.

At 0% of its no-load speed the motor is providing maximum torque but
doing no work (speed X torque = 0). This will be 5 to 10 times what
the motor can deliver continuously. Use it very sparingly (<1% duty
cycle).

P.S. for Dave:

I'm sorry you feel you had a "bad experience". I genuinely care that
people are satisfied with my designs. Beyond anything else, my pride
is wrapped up in doing the very best that I can.

I am an EE with no experience in the applications my drives are used
in, so it has been a learning experience for me. When I design
something I get guidance from users how they are applied and how they
can be made more useful. I then incorporate what I have learned in
the next version of the design. This is a synergistic process by
which the product evolves.

If I were smarter, I would forsee all possible eventualities and
design a perfect product straight off. Rather my situation is where
learn by iteration. It is a humbling process.

Where I have made an outright design mistake I have freely owned up
to it publicised to everyone who might be affected by it. Where I
have felt I have wasted someone's time while improving the product, I
have felt responsible to make up for it. I'm sorry your perception is
otherwise.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "Dan Mauch" <dmauch@s...> wrote:
> 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@r...]
> Sent: Monday, December 17, 2001 10:19 AM
> To: CAD_CAM_EDM_DRO@y...
> 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