Re: Connection of hardware

[johnm-at-slmd.com]

Jon Elson <jmelson-at-artsci.wustl.edu>-at-nist.gov on 01/14/2000 01:30:31 PM
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Subject:  Re: Connection of hardware


> 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 forsee a bunch of coding I'll have to do to obtain the spindle speed.

If I ask for 1300 rpm, it doesn't really have to be that exactly as long

as I know what it is (e.g., 1304.67 rpm) to coordinate threading tasks.

I'm a long way from getting there yet. I'm not going to use xemc as is

anyway since I want to personalize it (and I'm a X-Windows/Motif gui
expert).


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

There are opto-22 "quadrature" input modules that advertize to be used for
encoders,
but I know nothing about what I'm talking about, so I'm probably wrong :-(

See http://www.opto22.com/datasheets/1053_SNAP_Quadrature.pdf

They advertize that the max RPM allowed is 1,500,000 / encoder's pulses per
revolution

> 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 definitly want to build your emergency-stop-logic board. Please e-mail me
a postscript copy
so I can read all the part numbers. I have access to a electrical engineer
that
can show me how to make this board if I bring all the parts.

>
> 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


Thanks for your response,

John Moore