CLOSED LOOP QUESTION

Hello.

i have a disturbing question about closed loop, and true closed loop system.

looking at the centroidcnc website, they have the acorn, allin, and oak controller borads. i know closed loop mean the encoder feeds back to the drive, it's position, speed etc. but why some systems, the feed back are only between the encoder and drives, and others are from encoders, drives and controller card, i have seen this in AC servo systems, i am confusing about this because in the case of the acorn board, the specification say, it is NOT TRUE closed loop, and the oak controller board say it is TRUE closed loop, so what happen with the situation where the closed loop ends up in the drive, and the controller card does not receive any feedback signals? both are closed loop but what is the difference? if someone can explain me that please, i aprecciate it.


Noel.

With the loop closed in the drive only, the control just sends step and direction signals and the drive tries to keep the motor in the commanded position. The drive will have a preset following error which if exceeded, will cause the drive to fault.

With the loop closed at the control, the control can make adjustments to the commanded position on the fly if the motors are out of position. So if one axis starts to slow down, the control can slow the other axis to keep it in position. Not sure how useful this actually is.

Thank you Gerry,

yes i understand now, so in other words both are precise and accurate, as long do not exceed the speed or load, the controller closed loop will fix that right away, while the open loop controller will stop by the drive fault.
i suppose that under normal conditions the open loop will work fine even if it is a huge ac servosystem machine does't ? just trying to keep it well tuned