Closed loop steppers for CNC routers question.

[umnik]

I was watching several youtube videos demonstrating stepper motors with built in encoders with closed loop drivers. On first glance it looks good, they have all advantages of standard steppers plus more. In such systems they advertised as can be cooler running and have more torque on higher RMPs, and the prices looks quite acceptable (I checked against stepperonline.com). Could those drivers be used for usual CNC routers, do they have real advantages?
My main concern is as following. If such motor loses a step, then it may be corrected by driver and as a result the motor succeeds. Fine. But let say the router was cutting a circle, so two motors doing their work synchronously, and one motor was doing fine and another lost the step which was autocorrected by motor driver. Are such corrections fulfilled in timely manner so the effect will be unnoticeable or it may cause significant deviations in tool paths?
What your thoughts and experiences on that matter?

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[ger21]

If a stepper loses position, it's because it doesn't have enough power to maintain the position.
If it doesn't have enough power to maintain position, then how will it get back into the proper position?

The main benefit of a closed loop stepper is that it can stop the machine when it loses position.

But it's not going to be more accurate than an open loop stepper.

Open loop steppers should never be run at their limit. If you size them so that they have 25-30% headroom, they should never lose steps.

[Andreiir]

They lose steps , and dont recover if u go faster , but if u go slow then they dont lose steps , only main think is that are working more silent , and a litte faster than open loop .
The closed loop doesnt have more torque on high rpm , only help of encoder to move the motor , and not stall .