Safety circuit auto/manual reset

[BryanG]

You guys crack me up . Automatic restarting of a machine by just pressing the Emergency Stop Reset is of course not within the rules, but that isn't what I suggested. I said to split the safety in to two parts, one would be the Emergency Stop relay which would need a Reset and a Process Start. The second was the device that confirms the Safety Door is closed before the press can run. If you can tell me how having the operator perform two movements is safer than one, I shall be pleased to hear it.
I should state that I am not a Machine Press expert, but I watch "How It's Made", they close the gate, press one button, or press one foot pedal, or use two hands to operate a two hand system, and the press machine starts. They don't close the gate, press one button, then press another button, and then the machine starts.

 

[kallileo]

I should state that I am not a Machine Press expert, but I watch "How It's Made", they close the gate, press one button, or press one foot pedal, or use two hands to operate a two hand system, and the press machine starts. They don't close the gate, press one button, then press another button, and then the machine starts.

We have a Haas CNC lathe with interlock safety switch installed on the door that can't be opened when the lathe is machining a workpiece.
The machinist places the workpiece into the lathe, closes the door and presses Cycle Start button. After machining has completed it's allowed to open door to place the next workpiece, so he presses Cycle Start button and the machine is running again. No need to press Reset to start new machining cycle.

Only when the E-Stop is pressed, then the Reset button has to be pressed to restart the lathe. The same reset button also have some other functions like for example resetting the CNC code.

So it seems that it's possible for the machine to reset itself automatically after each operation cycle.

 

[Rson]

Please note that the section of the NFPA code refers to an Emergency Stop.

As mentioned, a light curtain or door switch may not be considered an Emergency Stop device, and the safety relay associated with either device can automatically reset. However, if an Emergency Stop is triggered (E-stop pushbutton pressed in, for example or pull-cord activated), you must have a separate action to reset the E-stop and start the machine.

If you had a light curtain and an emergency stop - you would have a separate safety relay for each in order to achieve the above. You could then just make the light curtain relay auto-reset, or allow the press of a cycle-start button to reset the light curtain relay. However, the E-stop relay can only be reset by the safety reset pushbutton.

 

[kvogel]

Looks like Rson beat me while I was typing my reply...



I would say no to both resetting the safety relay using the start switch or auto-starting when the safety system is reset.


I believe the best way to take care of this is to have the safety door switch auto-reset when the door is closed (on the transition of going to safe) and then the system can be cycled using the start button.



The safety system still functions properly and the number of operator motions is reduced. The auto-start can only apply to the closing of the door switch. E-stops and other safety devices would still need to be reset using the reset button if actuated. On startup, or a safety stop other than the door switch opening, the safety system would need to be reset using the reset push button with all safety devices in the safe position, including the door switch, before the auto start can become active.


This would require the use of a safety logic controller to accomplish and would of course be contingent to a safety review.


Cheers


Ken

 

[kwade]

You guys crack me up . Automatic restarting of a machine by just pressing the Emergency Stop Reset is of course not within the rules, but that isn't what I suggested. I said to split the safety in to two parts, one would be the Emergency Stop relay which would need a Reset and a Process Start. The second was the device that confirms the Safety Door is closed before the press can run. If you can tell me how having the operator perform two movements is safer than one, I shall be pleased to hear it.
I should state that I am not a Machine Press expert, but I watch "How It's Made", they close the gate, press one button, or press one foot pedal, or use two hands to operate a two hand system, and the press machine starts. They don't close the gate, press one button, then press another button, and then the machine starts.

My desire for clarification of statements made wrt safety circuits was not intended to be humorous or demeaning.
I was NOT saying that either statement was incorrect, just that taken together, both statements seemed to be at odds with each other.

I wanted to better understand the two following statements.

>I would use the Reset Button to also Start the process
>FPA 79 9.2.5.4 (2) The reset of the command shall not restart the machinery but only permit restarting.

 

[BryanG]

And I didn't intend to embarrass or upset, apologies if that happened, sometimes I type before I think. Good job I am not in International Politics . Or National Politics for that matter.