Runaway Easy servo

[dbsharp]

I have the Automation Tech version of the Easy Servo. I assume this is a rebranded leadshine drive. Overall the performance is great compared to the steppers they replaced. They do however have issues from time to time. However last night I had one runaway at full speed. Fortunately I just ran an endmill into a block of wood and it was soft enough impact not to damage anything. This motor will occasionally have an issue when its not been moving for a while and jog it; positional following error and the drive will instantly cut power triggering estop on my controller. This is what happened last night, but instead of killing power the drive ran away.

THIS COULD HAVE BEEN MY HAND. Is what I keep thinking. The way I have this motor geared, it can only generate about 300 lbs of force, but at that speed it would have gone clean through.

I would think that the drive would have addressed the failure modes to keep this kind of thing from happening! I guess this is not something they have to worry about in china?

So, I have been designing a conversion for my 13x40 lathe and I was going to use the same easy servo's but now I have decided to look for something with more robust safety features. As a crash like this on a running lathe could be very dangerous or damaging.

Can anyone recommend a drive that is safe under failure modes? I have been thinking of using DMM 400 watt servos, and I can see that they also use a more advanced methods of transferring encoder data back to the drive: "4-wire high speed serial encoder bus, with 8-bit security code for most reliable position feedback".

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[Jim Dawson]

The DMM servos do have encoder fail and other safety features built in. But like any servo they can run away under some strange conditions, but this normally does not happen. Most important is to wire them up like the diagram in the manual so they power up in an orderly fashion.

The condition that you describe above I have never seen with a DMM servo.