Estop Gecko Drives

[olf20]

Hi all, hope everyone is doing well!!
On another forum there is some discussion concerning Estops

It has been said that a Estop should stop all movement as quickly
and safely as possible.

If we do not use the inputs on the computer to preform a Estop
then removing power from drives etc seems to be the next order
of events to ensure the machine comes to a safe and immediate
stop.

My question is; Is it ok to turn off the DC power to the steppers on
Gecko 201 drives??

Any suggestion, comments are welcome.

olf20

[ger21]

No, never switch the DC power, it can kill the drive. I think switching it back on is worse than switching it off, but not entirely sure.

[olf20]

Thanks for the reply Gerry.
I was pretty sure that you could not disconnect the power
to the gecko drives / motors.
What does the industry do to ensure a quick and immediate
stop without removing power?
olf20

[ger21]

Servos with brakes.

[Crevice Reamer]

I'm not sure WHY you would not want to use the Estop, but it IS acceptable to switch off the AC power to the PSU.

CR.

[kawazuki]

Originally Posted by Crevice Reamer I'm not sure WHY you would not want to use the Estop, but it IS acceptable to switch off the AC power to the PSU. CR.

One caveat to that is the capacitance store on the DC input side! Some go overboard on this and can still move around for 10 - 15 seconds after switching off the AC power!
I did query this with Mr Gecko when using fuses in the motor feeds - he said its ok ! ! ! Can't see the difference - both cut DC but one good, one bad?

[The Blight]

As far as I could understand, cutting power is ok, but connecting power on the DC side is bad. So if you have the E-stop breaker on the DC side, you will have to switch off the AC side before resetting the E-stop. Sounds messy to me.

As far as I know, most gecko drivers have a disable function. Why not use this one? I believe it will cut all power to the motors, and it's safe to use. Check the manual for confirmation.

[MrWild]

You're forgetting the diode in the fused set up. When a fuse blows and there is innertia in the machine, it will produce power. Without a diode allowing the power to bleed back into the system, drive damage can happen.

Something that I had to get my head around with stepper systems is that stopping the step pulses, stops the motor. Period. No step pulses, no motion. Servos on the other hand can keep traveling with power stored in caps. Confusing aspects of the two can have you adding unneeded complexity.

Cutting power to the AC side won't stop a stepper that is getting pulses until the cap drains. Chopping DC will blow the drives without the diode to drain off the generated voltage as the motor stops spinning. Stop the pulses, and the drive stops turning the motor. BOBs with charge pumps on them will stop sending step pulses to the drives when the 15mhz signal s lost. They also have E stop circuits that stop step signals when the e-stop is hit.

[The Blight]

I also believe Mariss has made some tests to see what happens when you cut power on the DC side. As far as I can remember, he recorded som pretty high voltage spikes, but nothing that killed the driver (Stepper motor). The fuse is also placed after the capacitors, so once the fuse blows, there is no power to the motors. The table/head might keep on moving if there is not enough resistance to stop it from moving, but on most machines this wont even be a problem.

I know the PMDX-122 has a e-stop feature built in. It disables all signals to the data bus once the e-stop button has been pressed. This is a feature you can disable if you want to.

If you really want to cut power to the motors, you should take a look at the disable function.

[MrWild]

Originally Posted by The Blight I also believe Mariss has made some tests to see what happens when you cut power on the DC side. As far as I can remember, he recorded som pretty high voltage spikes, but nothing that killed the driver (Stepper motor). The fuse is also placed after the capacitors, so once the fuse blows, there is no power to the motors. The table/head might keep on moving if there is not enough resistance to stop it from moving, but on most machines this wont even be a problem. I know the PMDX-122 has a e-stop feature built in. It disables all signals to the data bus once the e-stop button has been pressed. This is a feature you can disable if you want to.

1. Don't confuse the G540 with 200 style drives. He addressed several issues with the G540 design that other drives may not be capable of. You can fuse the G540 with no ill effects without the diode across the fuse. I got the diode across the fuse info from a Mariss post of a few years ago (pre G203) which talked about fusing the 200 series of drives. (Things may have changed since then, but a 201 is a 201)

2. Several BOBs have the e-stop built in, its why all the talk of cutting mains power, or DC supply (for a stepper system) is way over kill

[The Blight]

1. Never heard about putting a diode over the fuse, but it does make sense. I'm using G201's and I have a fuse on the DC side. And as far as I understand, when the fuse blows, the driver is already dead. A fuse is simply just to slow. And I believe your right about the G540 being able to handle cutting the power on the DC side. I just thought the G201 could take it too.

2. Never said that it wasn't. Just pointed out that the disable function is a good way to cut power to the motors if he wants to. After all, if there is a fault in the electrical wiring in the machine (cutting wires or something), disabling power to the motors might be a good idea. Overkill maybe, but it's good to be on the safe side. I don't have this on my machines. I disable the signals only. Just to make sure I get it right. The charge pump circuit/signal is something comming from the computer right? The PMDX-122 can handle e-stop signals on board. It doesn't have to wait for the computer to register the e-stop before disabling the outputs. Is this the way everyone is doing it?

[bharbour]

Originally Posted by MrWild 2. Several BOBs have the e-stop built in, its why all the talk of cutting mains power, or DC supply (for a stepper system) is way over kill

This is valid in a stepper system. If a servo system loses the encoder, the motor will take off with no commanded motion, so the E stop needs to either pull the reset signal on the driver down (best) or switch off the drive power.

Bob