Re: Re: EMC's Conversation w/ Motion Controllers

Terry's right that the EMC is the motion control system. The PC running
the EMC's motion modules does all of the trajectory planning and computes
the cubic splines that are sent to each axis driver module to be
interpreted into steps or voltages.

The motion control cards used with the EMC like, STG, Vigilant, Studio
Ferraris, or Pico are basically dumb, real dumb devices. They read
encoder signals and report position to the EMC and they take digital
signals from the isa or pci bus and turn them into steps or voltages.

Most higher level motion control cards did all of the trajectory planning
in the card's hardware and all that was passed to them was some sort of
g-code or intermediate level language. The EMC uses an intermediate
level language, NML (Neutral Message Language) to communicate between
many of it's processes but that is not the language of any motion control
board that I know of.

It is this NML which allows us to separate parts of the EMC onto
different computers. We have demonstrated the ability to run a machine
using a graphical interface on a MS-Windows machine that talks to the
Real-Time Linux machine over an ethernet. There are several other
natural break points within the software that make it amenable to similar
distributed tasks.

It would be possible to use the EMC interpreter and take it's NML output
and pass that to some kind of program that translates that message into
the language used by a Gallil card for example. Such a system would not
use much of the EMC but just the g-code parser/checker would be of some
value to such a system.

Ray

>    From: "James Owens" <wotisname@...>
> Subject: Re: EMC's Conversation w/ Motion Controllers
>
> Hi Jack,
>
> I think you have your wires crossed, EMC is the control. It puts out
> pulses for step and direction of each axis via the parallel port to the
> driver cards. The exception here is with 0 to 10 volt servo drivers
> which may be internal or external to the computer. EMC can drive either
> stepper or servos with the right driver cards.
>
> Regards,
>
> Terry
>
>   What's the nature of the conversation between EMC and a servo motion
>   control card? Can EMC be reasonably viewed as a black box with g-code
>   and encoder signals going in and strings on some alphabet going out
>   to a motion control card? But what alphabet and what strings? What
>   kind of interface exists between EMC and the controller? I suppose
>   different controllers accept different sets of commands, so EMC must
>   have a place where interface code can be grafted on--right?
>
>   Thanks in advance.
>
>   Jack