Emergency STOP on mesa card 7i76e

Good evening everyone,

I was thinking to add an Emergency button to my machine.
I would like that when I press the button my card does not power off and the intention is to stop only the motion and the spindle and this is exactly what happen when I touch one of my limit switch.
Saying so my first thought is to wire the Emergency button in parallel with one of the limit switch.

I would like to hear some advice from the experts.

Thank you very much in advance for any comments.

Regards,
V.
 

It is best that an Emergency Stop not run through logic. You can add it into the logic, but it is best to kill the power to the drives directly by disabling a relay.

Hi, thanks for your answer
If I correctly understand what you are saying, what you are suggesting is to cut of power from the step motor driver.
If I interrupt the current to the drive there is not the chance to loose step in doing this?
I am thinking to restore job after emergency occurs so keeping steps is a key point.
Why you are saying that is best not to add emergency button to logic?
Thanks again.

E-Stop is just that. It is to stop the machine and stop damage to you or the machine.
Single block and feed rate override are used to stop a program during operation. You won't care about loosing a step to avoid a wreck or your hand. You can always rehome or set zero, your safety is far more important. If you have enough digits to count to ten when you start a job, the main goal is being able to do that at the end of the day also.

That's pretty good reason ! Inside me I knew the answer but I need some reminding to opt for your suggestion. Now I have to look around for some wiring diagram and hal implement code.

Thanks again.

Depending on your machine i would not just cut the power of the driver.
The axes might move free afterwards, z axis might fall down.
I cut enable and steps with safety relais so motors stop. Also spindle is diabled and Power cut after 10 seconds with safety time relais.

most estop buttons (well the ones I bought anyway) have two contacts. One is normally closed and the other is normally open.
Wire the mains power to your motors through the NC side and wire field power through the NO side. So when you push the button it cuts the mains power and lights up a Mesa input to tell Linuxcnc estop has been pressed.

This becomes a compliant system. You should not use relays in a safety circuit unless it is a standards approved  safety relay. The one I purchased cost me AUD $250 plus another $50 or so for the contactor which is required by the relay. Same story though. Drop power to the motors and signal to Linuxcnc that estop has been pressed...
 

thanks for your help

Thanks Mr Rod.
My emergency stop button is like that one you indicated, I have to do a bit of thinking about wiring and updating my hal file.
much appreciated your help

Well, my opinion is safety relays are overrated. They are just inputs and relays and microprocessors that is certified to work? Really?
I don't buy it, you can do the exact same thing with relay and inputs with mesa board. ITs electronics and whether it is in a certified safety relay or hard wired relay circuit, it will drop out relays when power is removed. I don't know about you but I have worked on many machines built from scratch and retrofits and I have never had a relay fail or an estop circuit fail. I have replaced a Siemens safety relay though on a Morbideli P2P router.
I see alot of the safety relays in large routers when retrofitting and I use them. I wouldn't pay for them if I had to buy them cause you can create the same  circuit with relays, timers etc...... Especially with the hobby machines 2'X4' and want to remove power from the drives on estop circuit and put safety relays in. A bit overkill don't you think? 

I can see maybe the need if you have a 10 foot 10,000 lbs router with a gantry that weighs 1500lbs moving at 700ipm, Mine I used the existing safety relay because it was there but it doesn't do anything magical, at least nothing you cant do with some relays etc...

Just my 2 cents and sorry for the rant,