Re: First time EMC user (introduction)

["Richard Everett" <rick-at-skyko.com>]

Hi again Ray,

I just talked to Marris also.  What a nice guy!  We went over all the
possibilities, and he described how the mulitiplier board works at very low
frequencies (down to 0 hz).  I ordered a G340 and two of the G902 boards to
convert my G320 drives.

We talked about encoder feedback to EMC, but since the gecko drive has a 128
count error signal (which would only be a fraction of a revolution of the
motor for my 10000 count encoder), I can use that as an indication of a
fault to EMC.

I still might move from the 350mhz K6 to my 1.4 ghz tbird, since the UI was
a bit sluggish even at velocity 5, and input 5000.

Thanks again for your and Tim's help,

Richard


>
>
> Richard
>
> Just a quick note to add to Tim's excellent post.  Marris indicated to me
> that the pulse multiplier works on the timing of the last pulse and the
> current one.  If you tune the 320/340 to your motor you will not see much
> loss of performance with the multiplier and it can be set for 2, 5, 10
> pulses out per pulse in.
>
> Since you have two 320's you just need two multiplier cards and a 340.
> If you added the dro card I mentioned, you'd be looking at something in
> the range of $300 and a bit of work to integrate opto isolators.
>
> Many commercial machines today use much higher resolution encoders than
> the positioning accuracy requires.  They do this to compensate for the
> fact of no tach velocity feedback for the servo drive rather than for the
> positioning.
>
> I take it that the existing drive amps were removed before you got the
> machine?
>
> Ray
>
>
> On Tuesday 01 October 2002 11:34 am, you wrote:
> > MessageYou should contact Gecko and ask about the details of how the
> > G901 works. From what Mariss had told me he is very happy with how the
> > G901 is working on the G340 drives and he tells me the low speed motion
> > is very smooth.
> >
> > You are correct that you will lose theoretical resolution with the
> > G901, but do you really need and is your machine capable of moving in
> > steps of 00002"? I doubt it. Increasing the step amount by 10 X  to
> > .0002" would not be noticeable in the real world unless you are running
> > some very high precision and temperature compensated equipment.
> >
> > Regarding the price, $150 per axis with not servo board is a LOT less
> > money than $200 - $300 per axis for amps and an $880 servo board. Yes
> > you will get slightly better performance with the STG setup, but is it
> > worth the extra $1K or so? Very doubtful.
> >
> > You might want to contact Gecko if you do want to go the traditional
> > servo amp route with a STG card and inquire about the ETA on the G310
> > units. It is a +/-10v servo unit with the same electrical specs as the
> > G320/340.
> >
> > It is all a matter of choices and trade offs like most everything in
> > life.
> >
> > Tim
> > [Denver, CO]
> >   ----- Original Message -----
> >   From: Richard Everett
> >   To: Multiple recipients of list
> >   Sent: Tuesday, October 01, 2002 9:51 AM
> >   Subject: Re: First time EMC user (introduction)
> >
> >
> >   Thanks Tim.
> >
> >   Two things bother me about the G901 boards (or the G340 drive which
> > includes that board).  It is a PLL (phase locked loop), which means it
> > needs several pulses before it "locks on" to that frequency.  I am not
> > sure, but this might be a problem on really slow moves.
> >
> >   The second thing is, by using this pulse multiplier board, I am sorta
> > losing the fine resolution that these encoders provide.  Are my
> > interpolated circles going to be somewhat more stepped?
> >
> >   At $39 per axis for the upgrade, I am looking at about $150 per axis
> > for drives (ignoring the fact that I have two G320 drives for the
> > moment).  Is there a true +/-10V input digital servo drive that takes
> > quadrature feedback in the $150 to $300 per axis price range?  I looked
> > around on the copley website, but all I saw that seemed to fit this was
> > the model 405, which is only 5 amps continuous, 10 amps peak.  I would
> > not mind getting the servo to go board (to have a closed loop system)
> > if I could find amps to fit my motors.
> >
> >   Richard
> >
> >
> >     ----- Original Message -----
> >     From: Tim Goldstein
> >     To: Multiple recipients of list
> >     Sent: Monday, September 30, 2002 9:20 PM
> >     Subject: RE: First time EMC user (introduction)
> >
> >
> >     freqmod.o will be worse than steppermod.o for your purpose. What
> > you need to do is get the G901 boards that convert the G320 into G340
> > drives. Then set them at 10x pulse multiplication. That will get you
> > down to 5000 step/in which is much more reasonable. Cost is only about
> > $35 per drive to upgrade.
> >
> >     Tim
> >     [Denver CO]
> >
> >       -----Original Message-----
> >       From: emc-at-nist.gov [emc-at-nist.gov] On Behalf Of Richard
> > Everett Sent: Monday, September 30, 2002 10:00 PM
> >       To: Multiple recipients of list
> >       Subject: Re: First time EMC user (introduction)
> >
> >
> >       Hi Jon,
> >
> >       I think I am in big trouble.  I looked at the fanuc motor encoder
> > on my mill, and it said 2500 counts/rev.  I thought to myself, wow!
> > 2500 counts in quadrature, thats going to be a lot of steps/inch.  I
> > loaded up emc with steppermod.o selected, and input and output set to
> > 2500, velocity set to 5.  I hooked up the gecko 320 drive to the motor
> > and parallel port, and directed emc to move 1 inch.  The motor rotated
> > exactly 1/4 turn!  My dang encoder is TEN THOUSAND steps/rev in
> > quadrature!!!  My ballscrews are 5 turns/inch, so I am going to need
> > 50,000 steps/inch!!!!!  It can't be done Jim!
> >
> >       I tried setting the input and output to 50000, and the program
> > never even fully loaded.  It got past the 5 second intro graphic, and
> > then just sorta sat there.  This is strange behavior....what is it
> > doing, getting pre-scared of the ini file?  I changed the input and
> > ouput in the ini file to 10000 and the program did actually load, after
> > 20 seconds (normally takes about a second after the intro graphic).
> >
> >       I am thinking even if I move from this 350mhz K6 to a 1.4ghz
> > athlon, I am still going to have big trouble getting rapids.
> >
> >       Would freqmod actually help this very much, or am I going to need
> > to dump the gecko drive idea and try and get a servo amp that takes
> > quadrature encoder inputs instead of a tach (I checked, there is
> > definately not a tach in there).  I don't mind buying something, as
> > long as it will work, and work at a decent speed.
> >
> >       Thanks,
> >
> >       Richard
> >
> >         ----- Original Message -----
> >         From: Jon Elson
> >         To: Multiple recipients of list
> >         Sent: Monday, September 30, 2002 8:29 PM
> >         Subject: Re: First time EMC user (introduction)
> >
> >
> >         Richard Everett wrote:
> >           Hi everyone, I have just installed EMC and linux using the
> > BDI cdrom image.  After figuring out that I had to log in as root, and
> > after setting the emc.ini file to steppermod and minimilltask (it would
> > not come out of estop with bridgeporttask) I managed to get step
> > signals on pin 3 (X axis) of the parallel port.  I monitored these with
> > my digital oscope, and saw an interesting thing.  I selected manual
> > control, and then set the x axis to move 1 inch.  My ini file had the
> > max acceleration at 2, and I captured the pulse train on my scope.  It
> > looked about right I guess, with the pulse frequency accelerating to 2
> > khz.  The strange thing was that after the pulse train had fully
> > accelerated, there would be a 1 khz pulse about every 8 or so of the
> > 2khz pulses.  I don't know if this is some latency issue, or perhaps
> > that is when some other task is running?
> >
> >         No, I think that indicates the granularity is set to 1 ms.  You
> > probably need to reduce the value of CYCLE_TIME in each axis.  Try
> > going to .0005 (.5 ms) then 00025, etc.  At some point, you'll either
> > hang the computer or make it VERY sluggish.  Back off a bit at that
> > point.  This will set the granularity of the step rate.  But, if you
> > really will me moving at rates of several thousand steps per second,
> > you may want to try freqmod.  It has finer granularity of the step
> > timing.
> >
> >
> >           I am running on an AMD K6-2 350mhz.  I am going to be using
> > this to control a rather large Shizuoka B-3V bed mill, with Fanuc model
> > 0 brush DC servo motors (60V 12A) on the x and y axis, and a Fanuc
> > model 5 bruch DC servo motor (90V 12A) on the z axis.  I am not 100%
> > positive, but I believe there is not a tach on these motors, just a
> > quadrature encoder (called a pulse coder by fanuc).  I already have two
> > Gecko G320 servo drives (take step,dir signals) which should work for
> > the x and y, so I am going to start with those.  I would get the servo
> > to go card, except that I am not sure if I would be able to use analog
> > input servo amps without a tach on my motors, so why not just get one
> > or two more parallel ports?
> >
> >         Yes, there are servo amps that can use encoder signals for the
> > velocity feedback from the motor. I'm a servo snob, anyway, so i would
> > recommend looking into these, instead of steppers, or pseudo-steppers.
> > I really think that DC tachs provide the smoothest operation at
> > extremely low speeds, but a fine resolution encoder can make it work
> > pretty well, too.
> >         You might also look at my parallel port motion control board
> > set at  http://pico-systems.com/PPMC.html It is slightly cheaper than
> > the STG, is not tied to the ISA bus, and has opto-isolated digital
> > inputs and outputs on board.
> >
> >
> >           Anyway, I want to really dig into this.  I like the idea of
> > an open source machine controller.  I discovered the (rather large)
> > message archives, and I will try to answer most of my questions there
> > so as not to clog the message board with redundant newbie stuff.  When
> > I get a bit more experience, I would like to add to the EMC knowledge
> > base, as I am going to need to do a few special things like controlling
> > my 20 position ATC on the cnc mill. Good luck,
> >         Jon
>
>