[pixpop]

I'm beginning to think that this device doesn't exist, yet it seems to me that it should. Been web searching and asking questions, but no luck so far.

What I have is an ordinary e-stop mushroom switch. You press the button, and it latches in the down position. You have to twist and lift to make it release.

What I want is exactly like that, but with the addition of a solenoid inside so that the switch can also be operated from an electrical signal. In either case, it would require the manual twist and lift to reset it.

Anyone ever seen such a thing, or care to speculate why it might be a really bad idea?

Neil

[MattTheNoob]

I have never seen such a beast, but there are certainly other ways to do what you are describing without mechanically actuating the switch.

[pixpop]

I have never seen such a beast, but there are certainly other ways to do what you are describing without mechanically actuating the switch.

But what I'm describing is mechanically actuating the switch. How can you mechanically actuate the switch without mechanically actuating the switch?

[MattTheNoob]

My point is that you can break your estop circuit without mechanically actuating the switch.

[underthetire]

No it does not. NFPA, OSHA, and CE all require the button to ONLY open the safety chain. All safety circuits are required to have a latching circuit, and and buttons in the chain must be able to open the circuit. Further more, just FYI, all Emergency stop buttons MUST be twist to release OR pull to release. They also require a separate "operator" to start the equipment back up, and MUST have a yellow ring around the push button.

Basically, to do what you want only requires the addition of a relay.

[pixpop]

I guess I didn't explain myself properly.

I'm not just looking for another way to break the safety circuit. Obviously, I could put any number of NO contacts in series to achieve this. They could be relay contacts, limit switches, or whatever. I understand that.

The machine will stop if the computer detects a fault condition, or if the operator presses the e-stop button. If the computer detected a fault condition, the operator has to take some action to resume operation.. clear an obstruction, or whatever. If the operator presses the e-stop button, he also must take some action, and then twist or pull up the e-stop button.

What I want is that when the computer stops the machine, the operator must twist/pull up the e-stop button in order to resume. I.e., I want that to be necessary regardless of whether it was the computer or the operator that caused the machine to stop. So, I thought a way to achieve this would be if the computer could press the e-stop button when it detected a fault. This would require an e-stop button with a solenoid.

Note that the computer would not need to operate the e-stop button in order to stop the machine. That would happen however it already happens, by removing power, applying brakes, or whatever. As an extra step, what the computer would do when stopping the machine due to a fault would be to also operate the e-stop button.

I'm a total newbie at this, so please excuse me if I'm being ignorant. This just seems to me how it should work in general. Anyway, it does seem that such a device does not exist. I have a spare mushroom switch, and I'll see if I can modify it to do what I want.

[Al_The_Man]

Traditionally E-stop circuits have either been the Mushroom push button that latches down and twist to release, or a two button setup that is a N.O. push to arm/engage in series with a N.C. E-stop push button, a control relay is picked up and the a latching contact is wired across the N.O. arming P.B.
A variation that is seen on imported R.O.C. equipment is a unit that combines both of these methods, it is a relay that has two buttons mounted to it, the start button actually pushes the armature of the relay and engages the latch contact so the relay stays in, the E-stop just cuts the power to the coil, dropping it out again.
If you want to conform to electrical code, one of the first two methods would be accepted, but the prevalent method now is to use what has been mandatory in Europe for some time and this is a Safety Relay, these can come in all kinds of configurations that allow controlled shut down with internal timers and switching combinations etc.
The bottom line is that E-stop circuits should be hardwired and not be Primarily dependant on software actions.
Al.

[underthetire]

OK, just have the computer break the estop chain, the operator would have to press control on to re-engage. Thats what the secondary operator is for. Per any code now, e-stop can not be self re-starting by simply releasing the e-stop switch. You must have a start or power on button to re-start the e-stop chain.

[pixpop]

...
The bottom line is that E-stop circuits should be hardwired and not be Primarily dependant on software actions.
Al.

Yes, I agree. I'm not proposing to change that. I'm proposing that, in addition to whatever else the operator must do to clear a fault detected by the computer, he must also twist the red knob and pull it up. For this to happen, the knob must be down, in the latched position, even if the operator didn't press it.

[pixpop]

Per any code now, e-stop can not be self re-starting by simply releasing the e-stop switch. You must have a start or power on button to re-start the e-stop chain.

Yes, I agree that's important. I'm not proposing that the e-stop would be self-restarting simply by releasing the e-stop switch. What I'm proposing is that in addition to whatever else the operator must do to clear the fault condition, they must also pull up on the red switch. In order for that to happen, the switch must be latched in the down position, even if the operator didn't press it.

I'm not proposing this as a new code, or a rule that anyone else must follow. It's just how I want my machine to work. But if this causes a safety issue I'm unaware of, I won't do it.

[underthetire]

Don't know why it would create any safety issues. My only concern would be if you have employees running the machine and you changed a factory E-stop circuit. If anyone should happen to get hurt and blame it on the switch, you'd be up for lots of explaining.

[Al_The_Man]

Frankly reading your explanation again, I don't see what the difference would be between what you describe and the typical control relay E-stop circuit, where a N.O. contact is used as a retaining contact across the Control ON P.B. any thing ANDED in the relay coil string will cause the E-stop to drop out and it requires the single P.B. by operator to reset it, which would be no different from releasing any other type you described.
A button with a solenoid or a contactor to have the same effect?
Al.

[Ashley Cobb]

Okay despite the fact that others have given you alternatives, I've been thinking about how to do this.

One way I can think of, without knowing what the internals of the switch look like, is this;

You would cut a ring from aluminium to glue to the underneath of the rim of the mushroom head. There would be 2 holes drilled at 180* to each other on the edge of the ring for pins or set screws. At the same point, drill 2 holes down through the ring, sized for the solenoid actuator.

Get 2 solenoids, drill hole for pin or flat for setscrew through the top of each actuator.

Determine how deep the solenoid is and if you need to either make mounts or cut holes in your panel to suit.

I'm very new to CNC so I hope this helps.

Ash

[Keith_W]

Hi pixpop,
You probably being in the states have an Allen Bradly Emergency Stop Pushbutton, this could be modified by attaching a shaft going through the center of the switch past the two tangs that press down to the NC Contact blocks into the head of the Actuating Head so a Solenoid can be fitted to the shaft pulling the head down mimicking the action of depressing the Emergency Stop Button.
If you did this and it works it would be a modification that would void the manufacturers warranty being Allen bradly, in the event of an accident and the Operator pressed the Emergency Stop Button and it failed you would be totally liable as you modified the switch.
Manufacturers like Allen Bradly etc have their units made to meet various standards so you would need to submit your modification to also meet these standards.
What I am saying is that allthough you idea is sound it isnt worth the trouble and expense to make it. The Emergency Stop is a complete separate part of the machine function and depending on its rating Stop Category 0, 1 or 2 is either hardwired as mentioned prevously or part of the machines computer system, if it is the computer system then that needs to be compliant with IEC61508 Functional safety of electrical/electronic/programmable electronic safety-related systems.
I would not modify the Emergency Stop circuit but modify the control circuit to acheive the outcome you desire.

Regards,
Keith.