Re: Connection of hardware

[Jon Elson <jmelson-at-artsci.wustl.edu>]

johnm-at-slmd.com wrote:

> Hello world of emc patronizers,
>
> I'm rather lost a little with how to connect everything together and maybe
> somebody could help me out.
>
> INTRODUCTION:
>
>    I have my pc running rt-linux with emc based code and a 4-axis ServoToGo
>    card.
>
>    I'm still selecting my n- axis servo-motors w/ drives, encoders and
>    limit switches, so I don't know what connectivity they will offer (e.g.,
>    an opto-isolated bread board with a 50-pin connector that plugs directly
>    to ServoToGo board ??)
>    [ I'm eyeing an IDC x-y positioning tables (RB6) with associated drives
>    (B8001) ]
>
>    Rather than a mill, I'll be adapting the emc code to run a lathe with
>    control of the spindle motor rotation as my third axis.

EMC is set up for 3 positioning axes.  I think there may be some
code in there to use another axis channel as a spindle speed command,
but I don't know if it was ever fully set up that way.  The problem is
that a spindle axis is kind of split.  You send a speed signal out the
A/D to cause the spindle drive to approximate that speed, but you
don't have any closed loop positioning.  The spindle position
comes back through an encoder, and is used to coordinate threading
tasks.  I think some or most of the code is in there for the
threading task, but the split up of the axis is not something I
know how to do.

>    I currently selecting my opto-22 racks and some I/O modules, so I'm
>    trying to decide which racks are appropriate.
>
> PROBLEM: Selecting I/O racks and modules
>
>    Question 1: What suggestions do you have in so far as getting I/O
>    opto-isolation racks?  (D-Series with field wiring terminal strip)
>      For instance, getting a SNAP 12-module rack (48 I/O connections) to
>      connect P1 and P2 and then a SNAP 6-module rack for the P3
>
>    Question 2: Does P3 usually connect directly to encoder I/O or is
>    another opto-22 SNAP rack needed?

I don't know of anyone using opto coupling of the encoders.  Generally,
the pulse rates are a bit high for general optocouplers.

I used Grayhill opto boards from Digi Key, as they were less expensive.
You can see what I'm using on my web pages at :
 http://www.artsci.wustl.edu/~jmelson/EMC.html 2nd picture
from the bottom,
and :  http://www.artsci.wustl.edu/~jmelson/CNCconv.html

I made an interface and E-stop board that watches the STG's
watchdog timer and other external e-stop conditions, and also
cuts off power to the opto boards if and E-stop condition
occurrs.  I've already made a circuit board design for this,
and am thinking about making it available to the EMC community
if there is enough interest.

Also, I'm working on a complete set of schematics on how to
hook up a 3-axis machine to a STG card and the parallel port.
I'll put that on my web site when I get it done.

Jon