Re: Re: CNC Closed Loop Control??

Hi Myron and Jason

I missed the first post so if this is NOT an EMC question, ignore this
post.

>    From: "Myron Cherry" <mcherry@...>
> Subject: Re: CNC Closed Loop Control??
>
> Jason, please reread my post of Feb 8 - I would like the same thing.

The EMC can read scales or encoders and still use step and direction.
The module to specify in the ini file is smdromod.o and the board to use
to read the scales is the Kulaga/Mauch dro card in an isa slot. You need
to specify input_scale as the number of steps your motor needs for a unit
of movement. Output_scale needs to be set to the number of pulses
returned to the dro card by a unit of movement. You may need to reverse
direction on one or the other of these with a minus sign in front of the
number.

If your machine has a lot of backlash you may have problems with this.
The motor will be winding up while taking up the backlash. When it hits
the end of the lash and begins to move the scale it may overshoot. We
have had this problem with servo systems.

Servo backlash compensation does not work here because it counts pulses
returned to create the compensation. With scales there are no pulses
returned while an axis is taking up the backlash. I don't have a clue
how stepper backlash comp might work. It seems that a bit of coding
might allow the stepper to move to take up backlash without counting
pulses on the scale.

> A
> utility or series of utilities could be written to answer all the
> questions (I think) the ini files need.

A year or two ago, I started a modular approach to doing this using
tickle but didn't generate much enthusiasm for it. It might still be in
the dropbox at www.linuxcnc.org. It's callled config.tgz and config.txt
explains how to use it. I have not tried it with a recent ini file but
it should work a bit.

Ray Henry

> I too would like someone else
> to do it because I'm not a programmer.
>
> Myron Cherry