Closed loop Step Servo Drive Driver 2HSS86H + 4.5N.M Motor + Encoder

[Jonathan]

Twinning an X, Accurate Z position over large time running jobs

If those are causing a problem, then it should be solved by setting up the system properly.

4th and 5th Axis positional holding. any CNCing that your likley to loose steps.

If you're likely to loose steps then you should choose a motor with a higher torque rating, since by the time the driver has corrected for any significant loss of position it could be too late.

Bear in mind that to make a stepper motor system closed loop, above a certain speed you don't need the encoder as the driver can monitor the motor back-emf and accurately infer the rotor position from that. For this reason, if you were to take the stepper motor from this driver and connect it to a driver which uses field oriented control (vector control), (e.g. 2M880N) the performance should be virtually identical above that speed. You can only gain anything below this speed, since whether the position is inferred from an encoder, or the back-emf, doesn't change the rest of the algorithm. That's the reason why the stall detect feature, e.g. on the AM882 driver, only works above 300rpm - it can't sense the position below that speed.
There will be slight differences, beyond the scope of this post, however these will be negligible compared to the gain you get from having a much wider selection of motor ratings with standard stepper systems - e.g. you'll notice the difference buying a 3Nm stepper instead of the 2Nm closed loop one as the closed loop one in general can't gain anything like 50% more torque from the motor.

There is potential for a gain in accuracy due to having the '1000 line' encoder on the stepper motor, however I'd argue that there are few DIY CNC systems which would benefit from correcting the position error that occurs when an torque is applied to an open-loop stepper motor, since it is so small compared to other inaccuracies in the system. Similarly, with an encoder the motor rotation can be 'smoother' at low speeds. Unless you're having big problems with resonance, this is unlikely to be an issue if the system is correctly designed.

Yes I agree.!!. . . . .It will take it to Another level of head ache.!
Normal steppers don't even come close to these even with good drives and servo's offer nothing more other than speed and torque unless used with control that can close the loop correctly, infact they offer less if the loop isn't closed because they can only fault if a following error occurs not correct for positional loss.

Servo motors are closed loop by definition. Whether you've got a closed loop driver on a stepper motor, or a more conventional motor, doesn't change the fact that the driver is continuously monitoring the following error. Following error and position loss are effectively the same thing - the closed loop control corrects for this error with both systems. With either system you should be able to select what happens when this error exceeds a certain threshold - i.e. loss of position.

Fundamentally, the only difference between this closed loop servo system and a standard servo motor is the number of poles and phases. Stepper motors generally have 50 poles and 2-phases, compared to around 2-6 poles and generally 3 phases for servo motors. That implies lower torque ripple, so smoother speed control, however any modern servo drive will use the field oriented control algorithm, which (if the bandwidth is sufficient) largely eliminates the torque ripple.

I certainly wont be buying any closed-loop stepper systems.