Re: EMC plc intergration

[Jon Elson <elson-at-pico-systems.com>]

Ray Henry wrote:

>Hi Lee
>
>I wrote this before you called but will send it to the list because there may 
>be others interested.  I can't answer your first question about using a 
>commercial PLC but have a few suggestions based on experiments I've done here.
>
>During the phone conversation you indicated that this is an older K&T machine 
>with switchable pole motor.  Indexing of the spindle for tool change is done 
>by ramming a pin into a hole in the spindle drive train.  
>
>As it sits now, the EMC does not have any provision for program control of 
>multi-speed spindles.  If you didn't need four speeds (2 motor and 2 gear) it 
>would be easier to handle by doing a gear change and running the VFD that you 
>are thinking about getting.
>  
>
Well, if you want to just command a speed, with the Sxxxx word, and have EMC
automatically figure out which gear and motor speed to use, no, it can't 
do that now.
It COULD be programmed in pretty easily,  though.  Hi-Lo speed range 
could be
selected using one of the spare M0x modal words and a digital output to 
switch
motor speeds.

>Tool change commands are available from the interpreter and will be passed to 
>IO programs like bridgeportio and tkio.  Fred Proctor once remarked that if 
>someone was holding a gun to his head, he'd write the PLC in Tickle using the 
>existing iosh.  In fact the sample program tkio is just about equivalent to 
>bridgeportio.  Both are software logic controllers that use an extra parport. 
>The principle of each could be expanded to include most any tool changer or 
>pallet changer or whatever logic you wish to build into your machine.
>  
>
If you were doing this using my PPMC or USC boards, I have made a hack 
to EMC
that puts all digital I/O through the RT section.  This allows you to 
have a constant
update rate of these I/O points.  You could use that to implement a high 
resolution
timer for events.  If the servo rate is 1 KHz, then counting off 1000 
cycles before
doing something would be a precise 1 second delay.  I'm not sure you can 
count on
delays being very predictable in Tcl, but maybe they are synchronized by 
EMC.


The other way to do this is to dedicate as many digital out lines to 
select what you need,
for instance if you have a 32 tool carousel, you'd need 5 lines to 
select the tool number,
1 line to command the tool change sequence to begin, and one input line 
to signal tool
change completed.  Then, use a PLC to handle the actual operation. 
 Programming the
EMC end of this should be very easy.

Jon