RE: [CAD_CAM_EDM_DRO] Re: Safety -- servo vs. stepper

Torsten,

Normally the limit switch actuates a power relay. In my case
this is a double throw that also applies a braking resistor.
There is a description on my engineering page.

A caution is in order about suddenly breaking the DC line
to the servos. They have some inductance, so such a break
will create a very high voltage spike (L di/dt). Sometimes
this happens in normal commutation (in DC brush motors) but
completely unhooking could damage the servo amplifier.

So as a further protection I have 100v Transorb devices across the
servo amp output. The system has worked well.

Another way is to remove power to the amp... but it may or may not result in
a regenerative breaking action.

A third way is to remove mains voltage from the supply. This prevents any
voltage spike, but a means must be made to rapidly discharge the filter
capacitor. I think Jon Elson has a diagram of this somewhere.

Leslie M.Watts
L M Watts Furniture
Tiger Georgia USA
(706) 212-0242
http://www.lmwatts.com
Engineering page:
http://www.lmwatts.com/shop.html
CNC surplus for sale:
http://www.lmwatts.com/forsale.html
CNC carved signs:
http://www.lmwatts.com/signwp.html




-----Original Message-----
From: Torsten [mailto:torsten@...]
Sent: Thursday, May 20, 2004 4:00 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: Safety -- servo vs. stepper


I have been contemplating about this for some time.
No solution I am fully satisfied with yet.
I am thinking about possibly running the Servos
dc powerline through the limit switches.
Anybody with any input about this?

When my encoder gets unpluged or malfunctions the
servos take off at full speed and there is nothing
the software would be able to do about it.

I plan on using seperate Home switches so during
normal operation no limit switch should ever be
triggered.

Is this a reasonable aproach on a feedbackless system?