Re: [CAD_CAM_EDM_DRO] Re: Geckodrive

Mariss:

Yes, it is an exciting possibility. Itll be good to have a "Fast as
Possible" selection under Feedrate.
Definitely the next generation... :)


Thanks,
Art
www.artofcnc.ca

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----- Original Message -----
From: "Mariss Freimanis" <mariss92705@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Saturday, April 29, 2006 2:21 PM
Subject: [CAD_CAM_EDM_DRO] Re: Geckodrive


> There's other exciting stuff that falls out using this method (step
> motor, encoder and G100):
>
> Let's say you are doing point-to-point X,Y positioning; maybe you are
> drilling holes in a printed circuit board. There are a lot of holes
> to drill and time is money so you want to go as fast as you can.
>
> If the axis are servoed to the lead/lag stall angles then the axis
> determine their own rate of acceleration and maximum speed. Both will
> be the maximum possible given the loads on the motors. Also, the axis
> dynamically adapt themselves to changing loads. Change load inertia
> and acceleration automatically adjusts, change fritional load and
> maximum speed automatically adjusts.
>
> The through-put will be far higher compared to set
> acceleration/velocity systems. My unloaded test motor accelerates
> from zero to 3,000 RPM in 180 degrees of shaft rotation.
>
> Mariss
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, art <fenerty@...> wrote:
>>
>> Hi Chris:
>>
>> >>> Perhaps I don't understand it based on what you are calling
> it. But
>> > as far as I know, every motor of every kind can be stalled with
>> > enough load on it.
>>
>> A matter of definition. It is stallable, if the pliers are held
> very
>> tightly the motor "stalls.", however, it can be called unstallable,
> because
>> it really isnt stalled at all, the hardware at that point is
> calling for no
>> movement. (You cant stall a motor that isnt moving..). In actual
> fact the
>> motor is holding itself at the maximum magnetic moment it can
> achieve
>> without "clicking" into the next position at which it will lose
> position.
>>
>> The Lead/Lag register in the G100 can measure up to 7 counts off
> target.
>> So imagine your moving at speed, the lead/lag is zero indicating
> the motor
>> is not going too fast, nor too slow, the necode agrees 100% with
> position.
>> SO a person puts their hand out and pushes against the axis's
> movement. The
>> Lag register at that point counts up to one, indicating that the
> encoder is
>> now one pulse behind. So the axis output stage , slows slightly to
> see if
>> the motor then catches up. This catchup is likely because the
> torque of the
>> motor has just increased a bit due to going slower. This is
> additive in
>> nature, the more you push, the more the output slows down and the
> higher the
>> motors torque. The trick here is speed. If the G100 can quickly
> enough
>> monitor (on a step by step basis) the lead/lag, then it can reduce
> the
>> ourtput speed quickly anough to produce an output speed correction
> that is
>> smooth enough to allow the motors torque curve to compensate in a
> curve that
>> assures fast enough correction time. This produces, for all intents
> and
>> purposes, an unstallable motor.
>>
>> It is planned, very shortly, for MachIV to start experimentally
> using
>> the lead-lag to have "Stall prevention" , since it cannot deal fast
> enough
>> as a program to produce the unstallable motor, a hardware feature,
> I was
>> thinking even under normal software control, you can have Lag
> determined
>> speed vectors. SO as the program sees up to 4 times a secnd the lag
>> registers, it should be possible during cutting to adjust the
> feedrate to
>> ensure the lag stays as close to zero as possible, in the odd event
> a person
>> has programmed a feedrate too high, or is hitting denser material
> in wood
>> and such. This "slow adjustment" has a possibility fo allowing for
> a small
>> correction in feed values in what I would call "Stall prevention"
> on the
>> application side. Not near as good a solution as Mariss's , but it
> may allow
>> one addition level of tool bit load smoothing. It'll be an
> interesting
>> experiment anyway. Im adding in the Lag registers use soon, cuz I
> did want
>> to play a little bit in that regard.. The functions of the MachIV
> trajectory
>> planner allow me some flexability n that area to apply corrections
> in
>> feedraet at intervals of 64ms or so feedrate variations.. A lower
> term
>> solution than an unstallable stepper, but one that also bears
> examination, a
>> corralary to a spindle load sensor of sorts..In fact , my plan was
> to simply
>> use it on the spindle output frequency, and see how it may work on
> axis
>> movement after that. In other words I intend to use "Lead/Lag" to
> regulate
>> the load on the spindle
>> output.. Im just waiting for the Spindle partition to be ready..
>>
>>
>> Thanks,
>> Art
>> www.artofcnc.ca
>>
>> Videos And Support Forums http://www.machsupport.com
>> Users Map: http://www.frappr.com/machsupport
>> ----- Original Message -----
>> From: "lcdpublishing" <lcdpublishing@...>
>> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
>> Sent: Saturday, April 29, 2006 8:34 AM
>> Subject: [CAD_CAM_EDM_DRO] Re: Geckodrive
>>
>>
>> > Perhaps I don't understand it based on what you are calling it.
> But
>> > as far as I know, every motor of every kind can be stalled with
>> > enough load on it. So, is it "Unstallable" in the sense the motor
>> > cannot be stopped?
>> >
>> > Or is it just closing the loop?
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
>> > <mariss92705@> wrote:
>> >>
>> >> Sorry for the cross posting but it's been a stellar day here.
> This
>> >> has to do with the "Unstallable Step Motor Project" that may be
> of
>> >> interest to some:
>> >> -----------------------------
>> >> Hi,
>> >>
>> >> The very crux of the G100 project is to have PID servoed step
>> > motors
>> >> that cannot be stalled under load. The G100 hardware was designed
>> > with
>> >> this goal in mind; that is why it has 6 encoder input channels,
> one
>> >> for
>> >> each axis. I have recently made/found the time to work towards
> this
>> >> goal.
>> >>
>> >> Before anyone asks "When will it be done?", don't. It will be
> done
>> >> when
>> >> it's done. A lot of steps, work and time stands between what has
>> > been
>> >> recently accomplished and a finished product.
>> >>
>> >> The goal: Imagine you are doing 3-D contouring (X,Y,Z) when
> someone
>> >> decides to sit on your gantry. An ordinary open-loop stepper or
>> > servo
>> >> motor would stall/fault-out and that would be that.
>> >>
>> >> Now imagine the overloaded X-axis servo-stepper would just slow
>> > down
>> >> under this load. The other axis (Y,Z) would slow down as well,
>> > keeping
>> >> their speed ratios with the overburdened X-axis. The 3-D
> contouring
>> >> path would be strictly maintained albeit at a much reduced speed.
>> > Once
>> >> your friend got off of the gantry, speed would pick up to where
> it
>> > was
>> >> before. Your work would not be ruined.
>> >>
>> >> How would this be done? Your step motors would be mounted with
>> >> encoders. The G100 would sense 1 or more motors are about to
> stall
>> >> (develop a phase lag of 1.8 degrees). The G100 would slow them
> down
>> >> and
>> >> back up the speed-torque curve to where more "grunt" (torque) was
>> >> available.
>> >>
>> >> Steppers have the unique characteristic of having a speed-torque
>> > curve
>> >> where the slower you go, the more torque that is available. Can't
>> > do
>> >> that with a regular servomotor.
>> >>
>> >> OK. That's the goal; that's the picture in my mind. Here's what
> has
>> >> been done by today:
>> >>
>> >> I have a G100 driving a G201 running a step motor at 3,000 RPM
>> > (NEMA
>> >> 23, 3A/phase, 24VDC). Open-loop, you so much as look at it and it
>> > will
>> >> stall. A flea landing on the shaft would stall it open-loop. I
>> > take a
>> >> pair of pliers and clamp down on a wet paper towel folded over
> the
>> >> motor shaft and all I get is steam. The motor will not stall. It
>> > slows
>> >> down under load but it delivers 50W to the paper towel/pliers
>> > combo to
>> >> make said steam. It goes all the way down to zero RPM without
>> > losing
>> >> position.
>> >>
>> >> I ease up on the pliers and the motor is back up to 3,000 RPM
>> >> lickedly-
>> >> split, gives a chance for the boiling-hot paper towel to cool
> off.
>> > Not
>> >> a step has been lost; you just can't kill the motor (stall it).
>> >>
>> >> This is just the first step (though a very important one) to
>> > integrate
>> >> the unstallable feature into a working CNC firmware. There are
> many
>> >> problems this feature presents.
>> >>
>> >> Just right now, having it do what it does, has me totally stoked.
>> > It,s
>> >> so cool, jerk down on the pliers, motor slows down. Instruments
> say
>> >> it's delivering 95%+ of all it has to give at all speeds. Let up
>> > and
>> >> bing-boom-bam, 3,000 RPM again. Just can't kill it no matter
> what I
>> >> do;
>> >> very fine Friday nite indeed.
>> >>
>> >> Before you ask #2: Yes, it will traslate into all step motors of
>> > all
>> >> sizes at all supply voltages at all speeds.
>> >>
>> >> Mariss
>> >>
>> >
>> >
>> >
>> >
>> >
>> >
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> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
> sister site to the CCED group, as many of the same members are there, for
> OT subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
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