Re: First time EMC user (introduction)

["Richard Everett" <rick-at-skyko.com>]

Hi Ray,

I responded to Jon with a rather long post, so I will not repeat all of that
here.  Thanks for the tips.  You were right, although I bet you didn't
realize my encoders are 10,000 counts/rev in quadrature!!!!  I need 50,000
steps to go one inch :-(

Time to rethink my electronics, huh?

Richard


----- Original Message -----
From: "Ray Henry" <rehenry-at-up.net>
To: "Multiple recipients of list" <emc-at-nist.gov>
Sent: Monday, September 30, 2002 11:26 AM
Subject: Re: First time EMC user (introduction)


>
>
> Hi Richard.  Welcome to the "Chips" (our mascot) fan club.  You may have
> seen him a few times during the install.  The micrometer is so that he
> can prove just how accurate the EMC can be.  The dead-blow hammer is to
> make the part fit!
>
> Steppermod is a binning procedure and may well produce periods of
> inactivity or reduced activity that will be obvious with a scope.  We
> generally speak of jitter when we consider how well it puts out pulses.
> You might try freqmod.  There you will find an attempt to generate
> frequencies rather than pulse batches.  Both of these are limited in
> different ways by the ability to generate pulse trains.
>
> The 350MHz PC should run freqmod with a period around 0.000035.  You will
> not get a real high speed pulse rate from it.  Better with steppermod
> than freqmod.  Better yet with a servo card. <hint>
>
> The machine sounds great.  There are a few commercial machines that have
> been retrofitted and a couple others who are working on integration of
> the EMC to this level of tool.  Most of these use or plan to use a full
> servo feedback system.
>
> Two things worry me just a bit about the Gecko 320 in this big machine
> application.  The first is that you will sacrefice a lot of speed for two
> reasons.  The first is that you will not get full current for the motors
> and that will reduce acceleration a bunch. The second speed loss will
> depend upon the number of pulses per unit of the existing encoders.  The
> Gecko pulse multiplier board might help this quite a bit.  You can think
> in terms of 5k to 10k pps for your computer so you need to see how many
> pulses it will take per unit of travel and then you will know the top end
> for rapids.
>
> The second concern is with open loop operation.  You should not loose
> pulses with the step and direction Gecko, at least not like you would
> with steppers but there is still something that bothers me about a
> computer making assumptions about where an axis might be on this big of a
> machine.  The Gecko will fault after 128 pulses sent to it are unanswered
> by the encoder but that can be quite a distance compared to normal
> following error settings for a servo system.
>
> It sounds like the encoders feed the drive amps and they compute velocity
> from the pulse train.  If this is the way the machine ran, those signals
> must also have been fed into the control for positioning.  You might well
> be able to make a single encoder do double duty with a PPMC (Jon Elson)
> STG,  Studio Ferraris, Vigilant, or whatever servo card(s) as well.  Or
> perhaps you could add a second encoder for positioning.
>
> You might look at tkio and iosh for a possible path to produce logic and
> work io pins for your tool changer.  There has been some talk about
> writing an interface that would allow us to use classicladder and MAT but
> it isn't there yet.
>
> M2CW  Hope this helps
>
> Ray
>
>
> On Monday 30 September 2002 11:14 am, you 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?
> >
> >
> > 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?
> >
> > 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.
> >
> > Back to the scope,
> >
> > Richard
>
>
>