Re: First time EMC user (introduction)

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

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