Re: Spindle Speed with the GS2 Drive

[Gene Warren <gwarren-at-execpc.com>]

  Hi Jon,

Jon Elson wrote:

>>
>> Some good news, and some not quite so good... EMC will control 
>> spindle speed via a spare DAC on an STG type card. It is open loop 
>> only and is currently set up for +/- 10V control. To add another 
>> parameter to the ini file to give a zero point offset would be fairly 
>> simple to do. The only danger here is the undefined state of the DAC 
>> prior to EMC being initialized might send your spindle of at full 
>> speed unless there is an enable input to the GS2.
>>  
>>
> You should ALWAYS use a solid state relay to control the VFD, by the 
> start-stop
> contacts.  That SSR should also be tied into the E-stop circuits.  
> When you have it
> set up right, it should always be in E-stop mode until the computer is 
> running EMC.


     You are absolutely correct, Jon, and I'm glad you brought that to 
the list's attention.  My E-STOP "string" will shut down all axis power 
and slam on the spindle brake.  It will not turn off the computer.  The 
E-STOP string will feed into EMC and tell it an E-STOP has occurred. 
 The E-STOP output of EMC will only be one function of the string.  The 
Westamp drives each have a drive fault output, as does the GS2 drive. 
 Any fault in any drive will halt the machine.  A big red mushroom 
pushbutton will be there. My E-STOP string will also be made up of dry 
contacts only.  The E-STOP from EMC will feed a solid state relay that 
will actuate a mechanical relay.  Every dry contact wired normally 
closed. Redundant?  I don't care.  I'm not going to be responsible for 
hurting someone if I can avoid it.

E-STOP out of EMC just means that EMC detected something wrong, not that 
the machine is safe.

     I have seen (and heard) a 3 foot round steel casting banging around 
in a 100 inch Bullard Vertical Lathe when the casting let loose from the 
fixture.  Talk about sending people to the bathroom with a spatula to 
clean their shorts.  The controller did not detect anything wrong, but 
E-STOP shut that sucker down when the operator slammed it with his fist 
on his way out of the area.  Now.

    I have seen (and heard) a 1 foot iron casting bend the hell out of a 
thick Mazak Lathe door as it bounced out of the chuck.   The machine 
controller did not detect that part missing and kept the spindle 
running.  Acted like a pinball machine.   E-STOP worked there.

     It is my firm conviction that the first design of any machine or 
retrofit should be a safe E-STOP string.  Then worry about getting it 
running.  I don't care if it's a table-top machine with stepper motors, 
or if it's the size of a 3 car garage with 30 horsepower servos.  When 
you hit the E-STOP you want stuff to stop.

As soon as I get some coffee I'll calm down.

Later,
Gene