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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 -----
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]
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 -----
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
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