Emergency STOP on mesa card 7i76e

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16 Jul 2021 10:21 #215017 by bevins
Replied by bevins on topic Emergency STOP on mesa card 7i76e

Good evening everyone,


Saying so my first thought is to wire the Emergency button in parallel with one of the limit switch.


Regards,
V.

 

I don't think that is a good idea for one reason is you can override the limit switch with one click of a mouse. With an estop you should not be able to operate unless you have cleared the fault, not click a checkbox.

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16 Jul 2021 11:51 #215023 by arvidb
Replied by arvidb on topic Emergency STOP on mesa card 7i76e

Well, my opinion is safety relays are overrated. They are just inputs and relays and microprocessors that is certified to work? Really?

Certification standards have been paid for with blood: accidents happen and then people figure out the standards needed to avoid them in the future. Safety relays have been shown to work with rigorous testing, and have redundancy. Can you say the same for your homebuilt circuit?

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.

This is exactly the same thinking that recently killed 14 people in a cable car in Italy . "I've worked with cable cars for 30 years and I've never seen a pull cable break, therefore I can disable both of the redundant emergency brakes instead of fixing them."

That said, I agree with you that if you have a hobby machine that cannot hurt you seriously then safety relays might be overkill.

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16 Jul 2021 12:45 #215044 by bevins
Replied by bevins on topic Emergency STOP on mesa card 7i76e

Well, my opinion is safety relays are overrated. They are just inputs and relays and microprocessors that is certified to work? Really?
Certification standards have been paid for with blood: accidents happen and then people figure out the standards needed to avoid them in the future. Safety relays have been shown to work with rigorous testing, and have redundancy. Can you say the same for your homebuilt circuit?

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.
This is exactly the same thinking that recently killed 14 people in a cable car in Italy. "I've worked with cable cars for 30 years and I've never seen a pull cable break, therefore I can disable both of the redundant emergency brakes instead of fixing them."

That said, I agree with you that if you have a hobby machine that cannot hurt you seriously then safety relays might be overkill.

Inside safety relays are inputs firing a relay if the inputs are clean. Some have microprocessors that can have logic failure.  Explain how this is different than having an input energize a relay.  

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16 Jul 2021 12:50 #215045 by scotth
Replied by scotth on topic Emergency STOP on mesa card 7i76e
I drive an SSR off of the 7i76E. On the 110 volt side, I drive the main control relay. The E-Stop switch is in series with the 110 volt side of the SSR, dropping power to the control relay.

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16 Jul 2021 13:00 #215048 by tommylight
Replied by tommylight on topic Emergency STOP on mesa card 7i76e
Not sure but the safety relays should be the ones that do not spark when switching, used in industrial machines, especially wood working ones as sparks and wood dust = big boom !

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16 Jul 2021 13:07 #215050 by bevins
Replied by bevins on topic Emergency STOP on mesa card 7i76e

Certification standards have been paid for with blood: accidents happen and then people figure out the standards needed to avoid them in the future. Safety relays have been shown to work with rigorous testing, and have redundancy. Can you say the same for your homebuilt circuit?

 

Absolutely I can say my circuits is the exact same thing as the Siemens and many other safety relays. There is no redundancy built into them whatso ever. Inputs firing outputs. That's all they are. just look at the schematics of a few. I dont know about the ones you are using but the ones that are used mostly in CNC are named safety relays because it is used in the safety circuit. Not because it has any extra safety features. Just look at the schematics.

You are being a bit over exaggerating comparing a life safety equipment that deals with humans than a 10 lbs gantry hobby machine.

just my 2 cents...

 

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16 Jul 2021 21:44 #215096 by rodw
Replied by rodw on topic Emergency STOP on mesa card 7i76e
Ooops, I got everyone started!

The thing your relay circuit does not have is certification under EN ISO 13849-1, or EN 62061 
There were 4 deaths near me because the estop was not pressed.... and safety features were removed and/or disabled.
www.bbc.com/news/world-australia-54321389
There is a big difference in a home machine but if you were building a machine for sale I guess it depends upon your risk appetite for litigation and criminal proceedings....
 

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17 Jul 2021 00:02 #215109 by JohnnyCNC
Replied by JohnnyCNC on topic Emergency STOP on mesa card 7i76e

in parallel with one of the limit switch


In parallel would imply that you are using normally open switches.  It is much safer to use normally closed switches.  In the case of a broken wire or bad switch you will find the problem before the switch is needed.  With NC switches you would wire all of the limit switches in series.
 
The following user(s) said Thank You: sibelius

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17 Jul 2021 08:48 #215125 by arvidb
Replied by arvidb on topic Emergency STOP on mesa card 7i76e

Absolutely I can say my circuits is the exact same thing as the Siemens and many other safety relays. There is no redundancy built into them whatso ever. Inputs firing outputs. That's all they are. just look at the schematics of a few. I dont know about the ones you are using but the ones that are used mostly in CNC are named safety relays because it is used in the safety circuit. Not because it has any extra safety features. Just look at the schematics.


This is the kind I'm talking about: Safety relay ABB RT9 . You can find them from other manufacturers too. They have redundant, short-circuit monitored "input circuits" (i.e. two circuits through emergency stop buttons etc) and also redundant outputs so that you can have two contactors in series to cut the power. They can also monitor the contactors for welded/stuck contacts though the contactors' auxiliary contacts.

I'm assuming this is the type of relay rodw was talking about earlier in the thread as well, considering he said he paid 250 $AUD for one!


You are being a bit over exaggerating comparing a life safety equipment that deals with humans than a 10 lbs gantry hobby machine.


There's no need to resort to trolling...

That said, I agree with you that if you have a hobby machine that cannot hurt you seriously then safety relays might be overkill.

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18 Jul 2021 06:33 - 18 Jul 2021 06:42 #215203 by sibelius
Replied by sibelius on topic Emergency STOP on mesa card 7i76e
 Hi everyone, 
This is a simple drawing of the wiring that I have in mind.
I hope you can read it.

I connected the Enable + and Enable - to the NO side of the Emergency button because in normal conditions (when they are not connected like at the present moment), the driver that control the stepper is Enable, so what I expect when I press the button is to close the circuit and consequently Disable the driver.
The other NC side of the button would be wired on the DC side of the driver power supply or maybe on the AC side.
If this is ok next step is to generate the signal to implement my hal file.

Thanks in advance for any help.
 
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Last edit: 18 Jul 2021 06:42 by sibelius.

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