|
Geckodrives 340 is intended to solve this problem and can be set to move
up to 10 encoder counts for every step issued to it. Andy
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
|