Re: First time EMC user (introduction)

[Jon Elson <elson-at-pico-systems.com>]

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