Bruce, Thanks for taking the time to explain it to me.
So I can take this approach then: 1) Use the internal E-Stop as an output on the BOB (Use this as in input to my AND gate) 2) Use the external E-stop which is normally closed as the second input to my AND gate) 3) Use the output of the Charge pump signal from the BOB as the third input to the AND gate. 4) The output of the AND gate to drive the TTL inputs of my AC Relays to enable/disable power to the motors. This way, I still have both E-Stops (Or additional ones by cascading E-stops) and the charge pump signal to rely on? I could make a PC board for an AND gate with Vcc and ground in with a decoupling cap and just bring the inputs and out puts to screw terminals. This way, it would be nice and modular, cheap and fit in any corner of my electronics drawer that slides in the computer rack. My spindle is a Hitachi router, so not sure if it is even possible to brake. It will get wired to a SuperPID so that I can control on/off and motor speed via software. I need to look at the documentation and see what I have available in terms of E-Stop control. It may be that I have to treat it like the stepper driver power supplies. I am just not there yet. I still consider myself a newbie so am trying to take it in digestible BYTES. As far as the external charge pump. I am thinking that LinuxCNC will only generate the carrier frequency (charge pump signal) when it has control. This way if the computer hangs or crashed I would at least have an additional level of safety. Or am I just over thinking it? Thanks again for your help. Joe ----- On Nov 7, 2014, at 2:35 PM, Bruce Layne [email protected] wrote: > Hi Joe, > > The industry preferred method of implementing an E-stop would be the > opposite of what you propose. Rather than using the mechanical E-Stop > switch as an input and logically ANDing the external E-stop switch and > the internal E-stop machine state, you should use the internal E-stop > machine state as an output and use electronic hardware (relay logic) to > AND the E-stop switch and the E-stop machine state to enable the spindle > motion and the X/Y/Z motion. To be clear, you're actually ANDing the > non-E-stop conditions, or NANDing two E-stop signals. However you want > to say it, motion should only be possible when the PC based controller > says it's OK to run, and when the E-stop switch says it's OK to run. > > The issue is the reliability of computer hardware and software. These > have greatly improved, but are still not up to the reliability standards > of relays. > > I like solid state relays, although E-Stop relays are usually clackity > relays with mechanical contacts. > > Consider using multiple E-stop switches if someone could be pinned by > part of the machine. Try think of all of the things that could go wrong > and make sure someone could quickly reach an E-stop. > > When wiring your E-stop circuit, make sure the E-stop switch contacts > are closed when you want the machine to run, and open when the E-stop > switch is activated. That way, if there is any loose connection in your > E-stop circuit, the wiring fault causes the machine to fail in the > E-stopped condition. > > The simplest E-stop wiring would cut power to the spindle motor and all > of your stepper motor power supplies, even though the spindle could > probably be actively stopped faster if left under power and commanded to > stop rather than coasting to a stop. > > Bruce ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
