Re: [CAD_CAM_EDM_DRO] braking resistors and current interupt estop

skykotech wrote:

>Hi guys,
>
>I need to add a hardware estop to my shizuoka cnc mill running EMC.
>I am running fanuc 0 DC brush servo motors on x and y (60volt ~10
>amp) and a fanuc 5 motor on z (80volt ~10 amp). I am running these
>off of the itty bitty gecko G340 drives, and they work quite well. I
>know that I want to have the estop button turn off the spindle motor,
>and I am guessing it would be a good idea to cut the power to the
>servo motors. :-) I found a box of 300 watt 5.1 ohm resistors and I
>have a bunch of 10 to 20 amp relays...
>
>Is the usual method to switch a resistor across the DC servo motor
>leads and simultaneously cut the motor power to each gecko drive? It
>seems it would be hard (large voltage spikes) on the gecko if the
>servo motors are disconnected...throwing a low value resistor in
>parallel with the motor leads would provide braking and drain the
>filter caps quickly...
>
>

No, there's a better way. I have a diagram of one such scheme.
See the 2nd schematic on http://jelinux.pico-systems.com/EMC.html
it uses one relay to charge up the capacitors in the servo drives through
the braking resistor, then after a delay connects the drives directly to
the power supply through a power contactor. When going into E-stop,
it connects the braking resistor first, then opens the direct connection
to the power supply. The diodes in the power transistors of the drives
connect the motors to the power supply terminals.

The contacts in my circuit applies 12 V to the enable terminal of my servo
amps. The Gecko 340 drives need a different connection, and you also
want to sense when any drive faults out. So, there would be some changes
needed.

Jon