[heavyweather]

Will I still have to gear down my motor when I use a closed loop stepper instead of a normal one?
My machine will have a GT2 belt with a 20teeth pulley so 40mm per rotation.
I will microstep the motor 10-20 maybe.
Some motor/deiver set like that.

https://www.ebay.de/itm/DE-STOCK-NEMA23-23SSM2440-Closed-Loop-Stepper-motor-2-9N-M-4A-Driver-HBS57-LONGS/263916291272?_trkparms=aid%3D222007%26algo%3DSIM.M BE%26ao%3D1%26asc%3D20180213162448%26meid%3D021b32 cd93cf4e6eb23ae6bc38d664d8%26pid%3D100930%26rk%3D1 %26rkt%3D8%26sd%3D263326838489%26itm%3D26391629127 2&_trksid=p2056116.c100930.m5375

My other option is a nema 23 with a planetary gear 5:1 or 15:1 reduction.
Freies schiff 3 stücke 4-Blei NEMA 23 reduktion getriebe Stepper Motor, Getriebe verhältnis 15:1, 20n. m
https://s.click.aliexpress.com/e/b834MfFE

[joeavaerage]

Hi,
if you have to gear a normal stepper down to do the job you'll have to gear down a closed loop stepper as well.

Being closed loop does not make it faster or more powerful or more anything really.....its just advertising hype.

Craig

[heavyweather]

Hi,
if you have to gear a normal stepper down to do the job you'll have to gear down a closed loop stepper as well.

Being closed loop does not make it faster or more powerful or more anything really.....its just advertising hype.

Craig

But being closed loop it will just try to reach it's position by applying more steps if necessary?
In that video it looks like the closed loop does indeed have more power?

https://youtu.be/vNjPo0wq8xI

[ger21]

But being closed loop it will just try to reach it's position by applying more steps if necessary

If it doesn't have enough power to maintain its position, then how will it have enough to regain it's position??

[PCW_MESA]

The difference is that a closed loop step motor/drive will recover position after a momentary
stall while open loop stepper will stall and have to be rehomed to continue

Other advantages of closed loop step motor systems are:

1. Lower power consumption/higher efficiency
( a open loop drive/motor spends most if its time pulling outwards or pushing inwards on the rotor to no great effect
other than generating heat, a closed loop drive/motor always pulls sideways to generate the required torque )
2. Higher accuracy via position feedback
3. Reliable stall detection

A closed loop step drive system will not change the basic stepmotor torque/speed characteristics,
as this is determined by the number of poles, inductance and drive voltage.
The high number of poles in a stepmotor (typically 50 poles) is what limits the maximum speed
compared to normal 4/8 pole AC servos

[joeavaerage]

Hi,

2. Higher accuracy via position feedback

I agree, a normal open loop stepper will hold position accurately and with high torque in full step and half step positions
only whereas a closed loop stepper can hold an intermediate position given the resolution of the feedback.

3. Reliable stall detection

I agree, a closed loop stepper can detect loss of position and may even attempt to regain it. A good, well specified
and tuned open loop stepper does not lose steps so detecting a stall is of limited value.My open loop steppers have not lost
a step in four years except if I was doing something stupid so I certainly wont be paying extra for something I don't need.

1. Lower power consumption/higher efficiency

I disagree, a stepper be it closed loop or otherwise is a variable reluctance motor and thus consumes power maintaining a magnetic
flux and subsequent holding torque. Feedback changes that not one jot.

Craig

[PCW_MESA]

Hi,

I disagree, a stepper be it closed loop or otherwise is a variable reluctance motor and thus consumes power maintaining a magnetic
flux and subsequent holding torque. Feedback changes that not one jot.

Craig

Feedback changes everything here because a closed loop servo (and closed loop step motors are true servos) only applies as
much torque=current as required to hold position, not full current all the time its in motion like a open loop stepper.
In fact closed loop step motors are often dead cool when idle or with low torque loads

[joeavaerage]

Hi,
compare the two torque/speed curves attached.

They come from the Leadshine site. The first is a 34 size 95mm long 3.5Nm (nom) open loop stepper. The second is their closed loop stepper.
34 size, 95mm long and 3.5Nm (nom), ie its the same motor with an encoder fitted.

Can you tell any substantial difference between the two sets of curves....I can't. Given that they are nearly identical how would you describe this quote
from your previous post?

In that video it looks like the closed loop does indeed have more power?

Craig

[islaww]

When you say: " (and closed loop step motors are true servos)", my first inclination is to wholeheartedly disagree. That said, can you point to non-marketing documents or tech bulletins that back up your claim?

[PCW_MESA]

When you say: " (and closed loop step motors are true servos)", my first inclination is to wholeheartedly disagree. That said, can you point to non-marketing documents or tech bulletins that back up your claim?

Why would you think that a closed loop step motor controller that does Field Oriented Control (FOC) and uses deviation in commanded to actual position
to modulate the torque plus uses the encoder to determine rotor position for commutation just like any 3 phase AC servo is not a true servo?
If you look up FOC and step drives you will find a number of references.

[joeavaerage]

Hi PCW_MESA,

Why would you think that a closed loop step motor controller that does Field Oriented Control (FOC) and uses deviation in commanded to actual position
to modulate the torque plus uses the encoder to determine rotor position for commutation just like any 3 phase AC servo is not a true servo?
If you look up FOC and step drives you will find a number of references.

I follow you argument regarding FOC....there is however a difference between an AC servo and a closed loop stepper, namely that the AC servo current
is modulated whereas the vector sum of the currents in a closed loop stepper are constant. The flux angle that results from the current applied is variable
but the flux strength remains the same.

As you know AC servos have a flat torque characteristic up to their rated speed unlike a stepper....look at the torque/speed curves I've posted
previously.....they are very different to an AC servo.

Craig

[PCW_MESA]

Hi PCW_MESA,



I follow you argument regarding FOC....there is however a difference between an AC servo and a closed loop stepper, namely that the AC servo current
is modulated whereas the vector sum of the currents in a closed loop stepper are constant. The flux angle that results from the current applied is variable
but the flux strength remains the same.

As you know AC servos have a flat torque characteristic up to their rated speed unlike a stepper....look at the torque/speed curves I've posted
previously.....they are very different to an AC servo.

Craig

Not true, most modern closed loop step drives use FOC and modulate the current (this is why they have nearly 0 idle power)

If you take a standard constant current step drive and close the loop by only changing the flux angle what you say would be true
but most closed loop step drives do not do this.

The torque characteristic is not a function of servo/open loop but mostly function of the high pole count and the concomitant
requirement of high frequency drive, this limits the current at high speeds and reasonable voltages.
That is, a 50 pole 3 phase AC servo would have similar characteristics...

[joeavaerage]

Hi,
my only experience with closed loop steppers comes as a result helping a friend with setting his ones up. They were constant
current types.

I am intrigued about your description of a stepper being a high pole count AC machine. I concede that the analogy is good.

The Achilles heel of any stepper is the loss of torque at speed. This was the problem for which my friend purchased close loop steppers,
it didn't work.

We concluded that the marked increase in resolution and loss of position detection were the only real advantages that a closed loop
stepper system offered. Your explanation that FOC can be used to advantage with respect to DC efficiency is not evident with his
hardware. Even if it were it still does not address the loss of torque at speed issue.

I hasten to add that the same high pole count allows a stepper to significantly out perform a servo at low speed in terms
of torque. Thus a stepper has a much higher torque density compared to a servo of the same size, at least up to speeds of
about 500 rpm. Over about 1000 rpm servos hold a distinct torque advantage given comparable size.

Given the premium that closed loop steppers attract (cf open loop stepper/drivers) relative to the modest advantages gained I concluded
that they are not worth the money. With a slightly greater expenditure genuine AC servos can be had.

Craig