SERIOUS violation of safety...

[Ryan P]

Ed,
All alpha Shopbots PRS and PRT old and new have the same type of Estop.

[ed_lang]

Thanks for getting me all straight Ryan.

I would have bet my new machine on the switch settings being different between my old machine and this new one.

Guess I am getting older than I thought.

One thing for sure, this goes to show you that asking a question on the Forum might give you the wrong answer. Ask ShopBot for the right answer.

[richards]

Depending on which machine you have, it would be very easy to install a Normally Closed momentary E-Stop switch that is in series with the coil of the main contactor relay. If a mushroom head E-stop switch were activated that required a twist to release, the coil would be bypassed and all power to the electronics inside the machine would be cut off.

I haven't taken the time to trace the signals on my PRT-Alpha to see how Shopbot uses the E-stop signal. They may do exactly what I'm suggesting or even have a much better method.

[richards]

I've received a few emails asking for a schematic showing what my last post was all about. The bottom part of the schematic shows how a common Contactor (GMC-22) can be wired to be self-latching. That means that when you turn on the main disconnect (not part of the schematic), you also have to push a momentary switch to activate the Contactor (SW1). When SW1 is pressed, it allows power to flow through the coil of the Contactor, which causes all of the contacts to close, including the auxiliary switch contacts shown at the bottom of the schematic. When the auxiliary switch is closed, the Contactor is latched on and will stay on until power is turned of OR until the E-Stop switch is opened (SW2). As soon as power to the coil is interrupted, all contacts open and the Contactor is disactivated until SW1 is pressed again.

This is a very basic circuit that does not require any on-board circuitry. Many of us who have built process control computers have used this type of circuit for more than thirty-years as a very basic safety circuit. As long as SW2 (the E-Stop switch) is a mushroom head twist-to-unlock type switch, it is about as fool-proof as anything available. Total cost for two idec brand 22mm switches and an 18A MEC GMC-22 contactor is about $75.00. Prices from other supplies varies greatly.


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[harryball]

I have checked inside the control panel and gone through the cable. The cable, though a little worn, is fine inside.

When I opened the switch I found this...


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The relay holder was lopsided but the switch worked over and over. It would not come off if pulled, it moved around a lot but worked otherwise.

I don't know that I've ever opened the switch since it was all wired up when I got it. I just dbl back taped it to the wall. I did remove the relay holder and properly reseat it then reassemble the switch.

Though there is a very good chance that was the problem I can only suspect since I was never able to get it to fail with the continuity meter attached.

For the moment, I'm going to call it solved.

/RB

[tmerrill]

A couple of years ago I installed a magnetic starter in the ShopBot's dedicated circuit. The real reason I did this was because my area tends to have numerous power glitches and outages and I wanted everything to stop immediately and require my action to start back up. Everything but the dust collection (Fein vacuum) goes through this switch.

I decided to position the switch directly over the computer station so it's red STOP button acts as a second emergency stop. If something was going real bad, before I would hit the spacebar I'd hit the red stop.

I haven't had to use it as an emergency stop yet, but during initial testing I did hit it when the ShopBot was in the middle of a cut and everything stopped immediately. For me, using a router with a manual on/off switch, this has the added bonus of shutting it off also.

Tim


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[harryball]

Very good idea... I wonder if I can put one on the shop. :-)

I can see the value in such a design just in piece of mind. I seriously need to take some time and move my shop around and add a few safety features like that. I have some great ideas... but never seem to find the time to actually do them vs. working.

I forgot to mention, I did snap the relay holder in properly before reassembling.

If such an event happens again I WILL replace the big red button with one of my own. I'll call it the Big Red STOP the #%$^& NOW button.

:-)

/RB