Re: First time EMC user (introduction)

[Ray Henry <rehenry-at-up.net>]

Richard

Just a quick note to add to Tim's excellent post.  Marris indicated to me 
that the pulse multiplier works on the timing of the last pulse and the 
current one.  If you tune the 320/340 to your motor you will not see much 
loss of performance with the multiplier and it can be set for 2, 5, 10 
pulses out per pulse in.

Since you have two 320's you just need two multiplier cards and a 340.  
If you added the dro card I mentioned, you'd be looking at something in 
the range of $300 and a bit of work to integrate opto isolators. 

Many commercial machines today use much higher resolution encoders than 
the positioning accuracy requires.  They do this to compensate for the 
fact of no tach velocity feedback for the servo drive rather than for the 
positioning.

I take it that the existing drive amps were removed before you got the 
machine?

Ray
 

On Tuesday 01 October 2002 11:34 am, you wrote:
> MessageYou 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 -----
>   From: Richard Everett
>   To: Multiple recipients of list
>   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 -----
>     From: Tim Goldstein
>     To: Multiple recipients of list
>     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
>         To: Multiple recipients of list
>         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