The control "hanged", I pushed the E-button and were going to turn power off and restart machine when the x-axis slowly "screwed" itself and the turret crashed into the tailstock..And there was nothing I could do but just stand by and se the **** happen. According to machine seller this had happend before on other machines.. What if som stupid operator tries to stop the turret from "falling" down, this could cause a serios accident...

What control and machine is this, it obviously has not been wired to either N.Amer or European standards as far as emergency stop requirements.
You need to check the electrical prints to re-connect for proper operation.
Al.

There was another thread about e-stop where someone discussed the estop button only telling the software, so if the computer had crashed, the machine was going to crash. After thinking about that, I re-designed my control.
Al,
I wired my control so that, in addition to disabling the drives, the power is removed from the drives. I suppose I could also dump the dc bus on the drives, is this commonly done? What standards should a commercial control follow?
Thanks,
Eric

What control and machine is this, it obviously has not been wired to either N.Amer or European standards as far as emergency stop requirements.
You need to check the electrical prints to re-connect for proper operation.
Al.


Its a Deawoo with fanuc 18i control. The E buttom works as it should, but not this time when the control "crashed".. Strange..

The control "hanged", I pushed the E-button and were going to turn power off and restart machine when the x-axis slowly "screwed" itself and the turret crashed into the tailstock....

This sounds more like a mechanical failure rather than an electrical one, If it is a slant bed lathe and the e-stop is operated the counter balance is often switched off, at this point it is common for a pin of some kind to operate to prevent the X axis from backfeeding and moving into the work or tail stockl.

Eric, The N.American definitions are a bit ambiguous (see PDF). Essentially the wording is that all power must be disconnected, but there is a clause to allow controlled shut down, where removing immediate power will cause damage to either personnel or equipment.
There are special relays called Safety Relays that have special features, especially for controlled e-stop shut down and protection, they are more common on European machinery but are getting popular here.
Al.

That reminds me of the time I forced the Z-Axis servo bit off on a vertical machine center. oops! The floor shock before I could force it back on. Boy, did I feel stupid, and in a customers shop. The machine had a motorized spindle and we were checking to see if the brake was draging, and I forced the wrong bit. Dang.....

On our slant beds and verticals we use a mechanical brake if the slide is belt driven. When the servo is powered down the brake engages. If it is direct drive, there should be a brake on the servo motor. Maybe that one failed? That's a bad situation tho. I hate it when stuff like that happens.

On most VMCs, the head is heavier than the counterweight. If there is not sufficient drag in the ways and ballscrew, the head can walk down when power is removed from the Z axis motor. I could see if this was a slant bed lathe, then the X axis could just not have enough friction to keep it in place. You could trying moving the X axis with the power off and see if it will move. If it it on dovetail or box ways, the gibs might need adjusting.