--- In Electronics_101@..., "lcdpublishing"
<lcdpublishing@...> wrote:
Hi guys,
I am working on version 4.0 of my CNC controller board. One of the
things I wanted to clean up was the E-Stop circuit for this.
This is how I would like it to work...
E-Stop is pressed...
Power to Motors is cut-off
Power to Spindle motor is cut-off
A logic level signal goes to all motor control chips
As I am mixing high and low voltages here, I know there are special
precautions I must take so as to not let the genie out of the bottle.
This is what I think I should have to make it all work...
The E-Stop actuator will have to contactors in it, 1 for logic and
the other for the power circuits.
1) Logic E-Stop contactor. When depressed, it takes that signal to
ground. Each of the inputs on the AVRs are pulled high with 10ks.
2) Power E-Stop contactor. Using a normally closed contactor, this
is to ground. When the butten is depressed, it is open. This
ground signal will go to the coil side of a relay(s) that switch the
power circuits on/off.
This should give me double protection (logic is off & power is off)
and it should keep the logic level voltages sepperate from the power
voltages etc.
I am sure I have something wrong as I usually do, but that's why I'm
asking :-)
Chris
There are standards. The normal Start-Stop circuit begins with a
normally closed Stop switch from one power rail to the junction of a
normally open Start switch and one side of the holding contacts. The
other side of the holding contacts connects to the other side of the
Start switch (they are in parallel, the holding contacts hold the
Start state) and this junction connects to one side of the coil. The
other side of the coil goes to common or ground. You really don't
want to switch an emergency circuit with a ground connection. Any
short circuit can simulate a ground connection.
The point is, it takes a specific action (pressing the Start button)
to get power but even the loss of power will cause the Stop function
to work. And the system won't restart.
A not particularly useful schematic is in Figure 7-16 here
Richard
