Re: First time EMC user (introduction)


Title: Message
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]
 
-----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
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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