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see my reply to Ray, but thanks Tim. I talked
to Mariss and he made me happy again.
I think I will be fine with .0002 (10X step
multiply) or .0001 (5X step multiply). I was not so much worried about
accuracy as I was precision. I don't care if the one inch diameter
interpolated hole is located +/- .0002 inches, or if the diameter of it is +/-
.0002 inches, but I would like it to be smooth.
Actually, for starters, I would be very happy to be
able to hold +/- .002.
Richard
----- Original Message -----
Sent: Tuesday, October 01, 2002 9:32
AM
Subject: Re: First time EMC user
(introduction)
You 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 -----
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 -----
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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