Re: [Emc-users] Speed problem with EMC

[Jon E. <el...@pi...>]

Tim & Heather Smith wrote:

>I had an interesting (read scary) moment with EMC today.
>I had used the mill (emc) early in the morning for a few minutes, and then
>left it all turned on for about 4 hrs before attemping to run the machine
>again.
>I ran a program which I had run succesfully in the morning (no changes), and
>emc had not been shut down. The machine took off at a speed way beyond what
>it was supposed to, and end up stopping with a following error(just before I
>could get to the E stop)
>. I have been playing around with a hot wire cutter mounted on the front of
>the mill, this really tested the breaking strain on the wire.....:)
>The way the machine is set up, at max speed I am getting no following error
>problems at all.
>
>The hardware I am using is Jon's USC and Gecko drives (Fantastic
>combination)also using BDI 2.20b.
>  
>
I have heard of this before.  But, how did it get a following error with 
no encoder
feedback to the computer?  Did the Gecko drive go to fault status?  
(That is a
different condition than a following error.) 

After recovering from the uncommanded move, did the machine run correctly?
Or, do you get a rapid motion as soon as the drives are enabled?  It 
sounds like
an encoder problem.  When not in motion, the Gecko drives will settle 
down close
enough to the servo null position that an encoder failure will have no 
effect until
movement is commanded from the computer.  Suddenly, the drives will go to
maximum output, but because there is no encoder feedback, the drives will
continue running away.

I would check all cables to the encoder for loose connections or shorts.

If it did get a following error, it may indicate that communication 
between the
computer and USC board has been interrupted, or possibly the USC board
has been powered off while EMC continued running.  Possibly a very short
power interruption could have caused this.  If this happened, EMC would have
gone to the ESTOP condition.  Did you notice that when you returned to use
it?  EMC sends some setup info to the USC when EMC starts, and that info 
will
be lost if the board is powered off.  Only restarting EMC will reset 
it.  I believe
position updates may not be made under this circumstance.  You might try
powering off the USC and then turn it back on, and see if it reproduces 
the problem.
While the USC board is off, the computer may be frozen.

Jon