> -----Original Message-----
> From: Dan Henderson [mailto:luvtof...@gmail.com]
> Sent: May-07-20 2:40 PM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Fluctuating RPM using CUI ATM 10 encoder
>
> Why certainly Gene (see attached). I actually have it working a little
> better now. My spindle-at-speed LED will start going bonkers around 1200
> rpm. I'm guessing this is when the counter "throws up it's hands and says -
> I quit!" lol. The spindle will operate all the way to around 4700 rpm but
> anything above this and the MC-2100 shuts it down -- must be some kind of
> voltage limiter kicking in then.
>
If you look at the source code for "encoders.c" John Kasunich's excellent
documentation says this:
"The driver exports variables for each counters inputs and output.
It also exports two functions. "encoder.update-counters" must be
called in a high speed thread, at least twice the maximum desired
count rate. "encoder.capture-position" can be called at a much
slower rate, and updates the output variables."
So if your encoder provides a quadrature count of 200 lines (800 quadrature)
and you turn that spindle at 4700 RPM (78.3333RPS) then 800 pulses/turn *
78.33333 turns/sec = 62.666KHz so your BASE_PERIOD must be at least 125kHz
(8,000 nS)
In your working example 1200 RPM is 20 RPS * 800 = 16,000 and twice that is
32,000Hz (31,250 nS BASE_PERIOD).
What is your BASE_PERIOD set at in your INI file?
Work it backwards. For example my PP HAL file says 24,000nS for the BASE
THREAD (41,667kHz). Assuming I have a 200 line encoder on the spindle then
41,667kHz/2=20,8333 and divided by 800 = 26 RPS or 1562 RPM. Since I want to
turn my spindle up to 3000 RPM that means either I have to decrease the
BASE_PERIOD (increase frequency) or reduce the spindle encoder count to about
100.
That means I need no more than 100 slots per rev on a disk. That's doable and
from what I've read lots of people can thread with that.
And, Sam Sokolik has been able to do rudimentary hex holes (although slowly)
with less than that.
Now since I have a MESA 7i92H all the numbers will change. I've not yet looked
at the MESA software.
Haven't even really followed the entire path from a
G33.1 Z-0.55 K0.025
to the Z axis motion in steps/second tracking spindle RPM.
John Dammeyer
>
>
>
>
> On Thu, May 7, 2020 at 2:29 PM Gene Heskett <ghesk...@shentel.net> wrote:
>
> > On Thursday 07 May 2020 13:19:23 Dan Henderson wrote:
> >
> > > I believe this is open loop. Isn�t PID only used in closed loop
> > > control?
> > >
> > Its (the PID is) a waste of processor time if open loop. I don't use one
> > of those in any spindle run by a vfd, the vfd is generally stiff enough
> > control by itself. If I thread on that machine, it will have a spindle
> > encoder, but its only job is to glue the axis motion being driven to cut
> > the thread, to the spindle rotation, in the case of a g33.1, going both
> > in and out of the hole. If you aren't useing a PID for the spindle, that
> > leaves motion I think.
> >
> > I think its time we saw your .hal file. Can you insert it into a mail?
> >
> > > On Thu, May 7, 2020 at 11:03 AM Gene Heskett <ghesk...@shentel.net>
> > wrote:
> > > > On Thursday 07 May 2020 11:27:57 Jon Elson wrote:
> > > > > On 05/06/2020 09:20 PM, Dan Henderson wrote:
> > > > > > I�ve confirmed the fluctuation occurs when spindle-at-speed is
> > > > > > configured. When I remove this feature, the spindle rpm appears
> > > > > > to stabilize. It�s almost like it gets caught in a loop trying
> > > > > > to chase its tail.
> > > > >
> > > > > This is VERY common in servo systems, and is due to delay in
> > > > > response of the object being controlled.
> > > > > You need to slow down the response of the PID to ignore the
> > > > > delay. This may be possible by adding
> > > > > D to it.
> > > > >
> > > > > Jon
> > > >
> > > > But my msg was that a near module generated spindle.N.at-speed was
> > > > never to be injected into any signal path leading back to a PID.
> > > > That near's output s/b only to that input to motion, and possibly to
> > > > an indicator led in the gui so the operator can be advised if its
> > > > acting funkity. Flickering could be worn brushes in a brushed PMDC
> > > > motor for instance.
> > > >
> > > > What you are describing as delays can often be fixed by the proper
> > > > re-ordering of the addf's involved for the oscillating axis. That
> > > > aspect of configuring LinuxCNC hasn't been mentioned recently or I
> > > > wouldn't even have included that paragraph in my reply.
> > > >
> > > > And from Dan's description above, I think this is an entirely
> > > > different critter from a timeing delay.
> > > >
> > > > Cheers Jon & stay well, Gene Heskett
> > > > --
> > > > "There are four boxes to be used in defense of liberty:
> > > > soap, ballot, jury, and ammo. Please use in that order."
> > > > -Ed Howdershelt (Author)
> > > > If we desire respect for the law, we must first make the law
> > > > respectable. - Louis D. Brandeis
> > > > Genes Web page <http://geneslinuxbox.net:6309/gene>
> > > >
> > > >
> > > > _______________________________________________
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> > > > Emc-users@lists.sourceforge.net
> > > > https://lists.sourceforge.net/lists/listinfo/emc-users
> > >
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> >
> >
> > Cheers, Gene Heskett
> > --
> > "There are four boxes to be used in defense of liberty:
> > soap, ballot, jury, and ammo. Please use in that order."
> > -Ed Howdershelt (Author)
> > If we desire respect for the law, we must first make the law respectable.
> > - Louis D. Brandeis
> > Genes Web page <http://geneslinuxbox.net:6309/gene>
> >
> >
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> > Emc-users@lists.sourceforge.net
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> >
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