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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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