EMC, Was Re: CAD experiment entry

Yes - exactly - that is the safest - and that is how Jon has his system setup. the thing that doesn't get powered down is the encoder counters. So you can come right back to the machine and turn it back on knowing exactly where it is. hell - you can move the table around manually and then take emc back out of estop and it knows exaclty where it is. (or use emc as a dro - but that is just crazy talk) ;)

sam

-- In CAD_CAM_EDM_DRO@yahoogroups.com, "Jeffrey T. Birt" <birt_j@...> wrote:

>
> >Another problem with the step/dir approach is you can't ever E-stop the
> >machine without having to rehome. I usually estop my machine whenever I
> >walk away from it, just click a button to bring it back online.
>
>
>
> That sounds more like a 'disable' state than EStop. An Estop system
> generally MUST remove power from the bits that move, that is what it is
> there for. There are some newer specifications for industrial system that
> can have a more relaxed EStop requirements, so on a large machine you don't
> have to remove power from everything to access a small area.These have all
> sort of extra safety gizmos and doubly redundant systems to make sure people
> don't get hurt or killed though and are not likely to be seen in the home
> shop.
>
>
>
> If your servos/steppers/spindle motor/etc still have power applied you are
> NOT in an EStop state. Be safe the life you save may be your own.
>
>
>
> Jeff Birt
>
> Soigeneris.com
>
>
>
> From: CAD_CAM_EDM_DRO@yahoogroups.com
> [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Jon Elson
> Sent: Friday, December 17, 2010 12:06 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: Re: [CAD_CAM_EDM_DRO] EMC, Was Re: CAD experiment entry
>
>
>
>
>
> timgoldstein wrote:
> > For the sake of those just getting involved, I want to point out that
> there are different approaches to servos. One is driven like a stepper with
> pulses being sent to the drive with each step telling the drive to move the
> motor 1 increment (usually an encoder pulse) and then the drive electronics
> tracking the movement and adjusting accordingly. In this setup it is open
> loop as far as the computer is concerned. So the controller program does not
> actually know where the axis being moved really is. A very viable and low
> cost servo approach that gives you the acceleration and speed benefits of a
> servo. I have my Bridgeport series II (known by all the old timers on the
> group as Bridgett) running Gecko G320 drives which are this style.
> >
> Right. The problem with Gecko-style drives is you have no way to know
> what the following error is. The computer sends the steps, and ASSUMES
> the drive has put the motor there. The old G320 had a fixed error limit
> of +/- 128 encoder counts, which could be quite a large error. I had a
> friend locally who had a G320 machine with high-resistance motors and
> only 36 V supply, and it would not return to the servo null. You could
> turn the motors 10-15 degrees and they would just sit there. Sometimes,
> after seconds, they would go "grrnk-grrkn-grrnk" and move back closer to
> the null point. This was not what I'd call tight servo control. Some
> other drives like the Rutex at least had a way to hook up a computer and
> get tuning and performance info out of the drive. (Not that I'm
> recommending Rutex here, they have other problems.)
> Another problem with the step/dir approach is you can't ever E-stop the
> machine without having to rehome. I usually estop my machine whenever I
> walk away from it, just click a button to bring it back online.
> >
> >
> > Speaking of hexapods, does anyone know of any hobby priced version or
> achievable DIY approaches? They are fasinating machines. If you don't know
> what one is you need to Google it. Maybe someone can post some links and we
> can talk about the pluses and minuses.
> >
> >
> I think the more-easily built ones are called hexaglides. They have a
> plate with several linear slides mounted to it in a plane. There are
> links between these slides and the platform. This avoids having to make
> extremely good telescoping rods.
> >
> > But, I talked to Art about it once. Not sure if he would admit to it in
> public, but what he told me was every time he added a button or widget to
> the screen he sold more licenses.
> >
> >
> Well, adding a FUNCTION that wasn't available before certainly can
> expand usage in new areas. We do it in a different area, many of the
> smaller enhancements are accomplished by finding new and ingenious ways
> to reconnect stuff in HAL to bring out things to display on the
> customizable part of the GUI. I added an MPG with a filter to prevent
> the coarse MPG counts from "buzzing" the servos, and a spindle speed
> display with filtering to stabilize the displayed value, and a
> rate-of-change limiter to the spindle speed, mostly for use when rigid
> tapping, all in HAL scripts, without touching a single line of the EMC
> code base. HAL is the big new thing when EMC became EMC2, the
> brainchild of John Kasunich. It is a scripted language and framework
> that connects all the major components of EMC2 together, and allows you
> to make new connections for all sorts of functions.
> >
> >
> > I have to disagree on this. I have full closed loop servo machines, open
> loop servo machine, and stepper machines. They all work and make fine parts.
> Different capacity and performance, but all capable of making a to tolerance
> piece.
> >
> >
> Steppers are fine for things where the speed ratio is modest and the
> forces are quite predictable. Metal machining is just not that
> predictable, so the only way to avoid position loss --EVER-- is massive
> overkill. I'd mich rather have a wimpy machine that TELLS me when it is
> overloaded than one that will just try to bull its way through concrete.
> > Jon, can you also post a link to where someone can get more details and
> pricing on your products for servos?
> >
> >
> Sure, http://pico-systems.com/oscrc4/catalog/ is my web store, and most
> of the stuff there has links to the "back pages" with more
> detailed descriptions. The PPMC (analog servo interface) has been
> relatively unchanged since 2002, the Universal Stepper Controller
> has been out since 2002, and my PWM controller and matching servo amps
> have been out since 2004.
>
> Jon
>
>
>
>
>
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