Kinetix 5500 not turning on motor brakes with 3-phase loss

CapinWinky

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Aug 2011
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I have a hanging load on a Kinetix 5500 and we are experiencing crashes if we lose 3-phase power during operation. The 24VDC power is still live, so the PLC and safety circuit are still up when this happens. Our Bus voltage is normally 680VDC from our 480VAC input.

The drive is recognizing the drop in DC Bus voltage and produces a message that it is lowering the torque limit. That is insane to me; why would it take it upon itself to lower my torque instead of just faulting out. The "Action to take upon exception condition" for Bus Undervoltage Factory and User limits is "StopDrive". I don't see any UnderVoltage Limit parameter anywhere in the Axis parameters, so I don't know what those limits are.

I need this thing to turn on the brakes if it loses 3-phase, not go limp-wristed and crash my ****. What's the best way to go about this in a bulletproof way? Do I need to monitor the voltage myself with a GSV and throw a MAF or is there some setting I'm not seeing that will make the drive do this on its own?

EDIT: The reason this thing regularly loses 3-phase power is out of my control and customer required. It is just a thing I have to expect to occur regularly and deal with.
 
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My understanding is that the brakes on those are not intended to stop a load, only to hold the motor once it is stopped. So any time the encoder is changing values (motor spinning), the drive will not set the brake. The only bulletproof way to deal with a vertical load is to have an external brake that is designed to stop the load under conditions like this.

I am far from an expert but we have dealt with what you are going through, I looked at some parameters for a vertical load and stop action is set to "Current Decel & Disable" Shutdown Action is set to "Disable" and most all of the exceptions are set to "Shutdown"

I think the problem with "StopDrive" is that under 3 phase loss, it cannot stop the drive because there is no torque/power to do it. And it won't set the brake because the motor is spinning.
 
As I recall, the brake control is just an on/off control. I don't think it cares if the brake on the motor is designed for stopping under power. Motors can be specified to have no brake, a holding brake or one that can stop it under power.
Regardless (and I don't have access to check at the moment), I think you will have to change the setting from "Stop Drive" to "Disable Drive". The brake output should turn on (mechanically disengage the brake) whenever the servo is enabled and turn off (mechanically engage the brake) whenever it is disabled. If I get a chance to look into it deeper, I will update this thread.
 
On every drive system I've ever touched, motor brakes are released a set amount of time after drive control current it turned on and set a set amount of time before the removal of drive control current. You absolutely want your brake to deploy regardless of motion if the drive loses power and that is the default behavior on everything I've worked with, except Kinetix apparently.
 

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