Re: [CAD_CAM_EDM_DRO] "lost steps", what is it and how do you know you lost 'em?

Monte Westlund wrote:

>I think I know what the term "lost steps" is describing, but how do
>you know that you lost them? Is it a stepper motor thing only? I'm
>putting together a Taig mill with servo's, Gecko 320's (Camtronics
>kit, if it matters, but I don't think it does) and demoing Mach1 (I
>don't think that matters either, could be any step and dir
>controller program). I've read about servos and the encoders sending
>feedback "back to the computer", but in this sort of setup the
>encoder feedback isn't going "back to the computer", is it?
>
>

No, the computer does not have position feedback.

>The control program is feeding step and dir to the drivers. Are the
>drivers making sure that no steps are lost? Is this a true "closed
>loop" system, or just a way to use a step and dir controller program
>with servo motors, but still with the possible problem of lost steps?
>
>

It is closed loop between the drivers and the motors, but mot between
the computer and the
motors. Yes, the drivers compare actual position to the step pulses
received, and will fault
if the error gets to be too much. If you want closed loop to the
computer, so that following error
can scale with velocity, so you can move the machine manually and see
the position change on
the screen, so position won't be lost after an emergency stop, you won't
get it with the Gecko
(or other step/dir to servo) systems. If your encoders send signals
reliably to the Gecko drives,
and the computer-Gecko link is also working right, then you won't lose
steps.

Jon