Servo motor speed control

ASF · Mar 24, 2021

Hi all,

Got an application where the customer is looking to use a servo motor, purely because of the very wide speed range required for different products, which makes conventional drives impractical. So we don't need any motion or positioning - just need to be able to drive a servo at a given speed.

My initial thought was a Kinetix 300 and a TL series servo motor. Everything else is on Powerflex 525's with Ethernet/IP control and safe torque off, so this would keep the overall design much the same, just with a different box.

But what I don't know is, do I need a motion-class PLC to drive it, even if I'm not doing motion per se? Again, I'm not interested in positioning as such, only speed control (I will also need speed feedback from the encoder), but I've never spec'd a servo motor before so I'm not sure whether or not I need a PLC with an "M" in the part number. We're currently using a 5069-L320ERS2.

Also open to other, simpler suggestions - primary objective is speed control over Ethernet/IP, with encoder speed feedback (also over Ethernet/IP) and safe torque off.

g.mccormick · Mar 24, 2021

What speed range are you needing? If this is just speed control, could a "standard" closed loop drive not work? Many drives will go to 400hz and many can also be used with PM type motors not just squirrel cage.

GaryS · Mar 24, 2021

A Servo i a very poor choice for you needs
a Flux Vector drive is the way to go 1:1000 speed range
i have run them from .2 hz to over 200 hz
much easier setup all standard hardware
i would recommend that with any motor you intend to run at over 5000 rpm have the motor balanced for the higher speed

ASF · Mar 25, 2021

Thanks for the advice - if we can make it work with a standard VSD and motor then that's the way we'll go. The initial information I got was that this wouldn't be possible, but if anyone can prove that wrong, they'll be on this forum I'm sure

There are three motors requiring this treatment, turndown ratio ranges from 15:1 to 54:1. Forced cooling is not really an option, so we probably don't want to run the motor any slower than maybe 15Hz, meaning that the upper end would be around 800Hz. Ultimately, we need to achieve a gearbox output shaft speed of 0.75rpm...40rpm.

GaryS · Mar 25, 2021

I have running about 2 miles from me on a milling machine on polish cycle they run the VFD at .2HZ
You really have to look close to see the mill head move.
As I said I have others with the top output frequency of over 150hz
I have many machines that I have replaced the servo motor and drives with the A1000 Flux Vector Drive
For the motor I usually use a Marathon Vector duty motors.
The A1000 drive is being phase out and replaced with GA800 my understanding is that it has better performance and more features I would be looking at it for this project.
I generally select rating a little higher side just to give me a buffer.
According to the ratings of both the VFd and motor you can run then at 100% torque at Zero speed for as long as needed. I have used them on crane hoist for years and I always stop the motion for about 10 sec. (Suspending the load on the motor ) before I set the brake this results in zero ware on the brake
We actually measured one after 5 years of heavy use we had no measurable ware on the brake pads
As for your low and high output frequencies, they are way out of line
You can easily run the vector duty motor way below 6 hz all day long
I have a welding machine with 2 sub arc heads up to 600 amp on each head if I remember the lowest weld speed is at 0.5 hz we could run it slower but that what they want.
And for your top at 800hz. A 4 pole motor 1800 rpm base speed would be running at over 24,000 rpm’s
that would take a very special motor to handle that and of course the gear box would have to rated for that same speed and torque. It starts getting complicated and expensive.
Just make sure you size the motor, VFD and gearbox for the load and speed requirements, it’s always better to have a little more than needed than come up short.
If your output speeds are correct that only about 60 to 1 that no problem at all it’s a lot easier that some of the projects I have had running for years the Flux Vector VFD is rated to 1:1000 speed range
If you were closer I would say you could have come in as help you but I just don’t were you will have a problem setting it up

Lynx777 · Mar 25, 2021

To answer your first question. No, you do not need a motion class PLC for the Kinetix 300. The Kinetix 350 however does need a motion class PLC. They look identical at first glance.

jraef · Mar 25, 2021

There are VFDs out there that can go to 1,000 Hz output. But I doubt you can get a motor that can operated at that speed without going to a custom "spindle" motor. Also, anything over 599Hz typically requires special permission from your Government to allow the VFD (or servo for that matter) to be programmed to that speed. Drive mfrs that offer it are supposed to put a "lock" in the programming to enable it and you can only get an unlock code by certifying that you have been given permission to use it as a "high speed drive". This has something to do with VFDs being used on centrifuges to enrich uranium.

https://www.motioncontroltips.com/faq-how-does-eu-regulation-4282009-apply-to-ac-drives/

ASF · Mar 25, 2021

GaryS said:
I have running about 2 miles from me on a milling machine on polish cycle they run the VFD at .2HZ
You really have to look close to see the mill head move.
As I said I have others with the top output frequency of over 150hz
I have many machines that I have replaced the servo motor and drives with the A1000 Flux Vector Drive
For the motor I usually use a Marathon Vector duty motors.
The A1000 drive is being phase out and replaced with GA800 my understanding is that it has better performance and more features I would be looking at it for this project.
I generally select rating a little higher side just to give me a buffer.
According to the ratings of both the VFd and motor you can run then at 100% torque at Zero speed for as long as needed. I have used them on crane hoist for years and I always stop the motion for about 10 sec. (Suspending the load on the motor ) before I set the brake this results in zero ware on the brake
We actually measured one after 5 years of heavy use we had no measurable ware on the brake pads
As for your low and high output frequencies, they are way out of line
You can easily run the vector duty motor way below 6 hz all day long
I have a welding machine with 2 sub arc heads up to 600 amp on each head if I remember the lowest weld speed is at 0.5 hz we could run it slower but that what they want.
And for your top at 800hz. A 4 pole motor 1800 rpm base speed would be running at over 24,000 rpm’s
that would take a very special motor to handle that and of course the gear box would have to rated for that same speed and torque. It starts getting complicated and expensive.
Just make sure you size the motor, VFD and gearbox for the load and speed requirements, it’s always better to have a little more than needed than come up short.
If your output speeds are correct that only about 60 to 1 that no problem at all it’s a lot easier that some of the projects I have had running for years the Flux Vector VFD is rated to 1:1000 speed range
If you were closer I would say you could have come in as help you but I just don’t were you will have a problem setting it up

Thanks Gary, this is great info. So, if I understand correctly, there are specific "vector duty" motors available that can be run on a flux vector drive, and are rated to run at very low speeds continuously with no external cooling? If that's the case, I'd definitely be pushing back with that as the preferred option.

I've never had much involvement with spec'ing the motors themselves - I've always just been the code monkey who makes them go round and round after someone else specs them! If I were going to a motor manufacturer like SEW or Nord, looking for a motor than can be run on a flux vector drive at 2Hz or 100Hz all day with no requirements for external cooling etc, what would I ask for? Is "vector duty motor" enough of a description?

jdbrandt · Mar 25, 2021

ASF said:
Thanks Gary, this is great info. So, if I understand correctly, there are specific "vector duty" motors available that can be run on a flux vector drive, and are rated to run at very low speeds continuously with no external cooling? If that's the case, I'd definitely be pushing back with that as the preferred option.

I've never had much involvement with spec'ing the motors themselves - I've always just been the code monkey who makes them go round and round after someone else specs them! If I were going to a motor manufacturer like SEW or Nord, looking for a motor than can be run on a flux vector drive at 2Hz or 100Hz all day with no requirements for external cooling etc, what would I ask for? Is "vector duty motor" enough of a description?

I've used BlackMax motors, attached to servo drives, and had really good results. (Offset printing infeed, following a real master from the motion control) You might need an external fan, if you run at low frequencies for too long.

Gene Bond · Mar 26, 2021

There are 2 different types of 'Vector Duty' motors which are rated for 1000:1 or so speed range. There are TENV (Totally Enclosed Non-Ventilated) and TEBC (Totally Enclosed Blown Cooled).

TENV motors are typically finned Aluminum frame motors, which have enough surface area to dissipate the heat loss, without external air flow. Thus, they can cool themselves without turning.

TEBC motors have a separately powered fan/blower built onto them so the cooling air is the same regardless of the main motor speed.

TENV are typically lower HP, like up to 20 or so, and TEBC go all the way up to 100's of HP.

James Mcquade · Mar 26, 2021

Since everything else is a powerflex drive, may i suggest that you use the same type of drive and keep the customer happy. nothing new to buy or learn.
james

ASF · Mar 28, 2021

Gene Bond said:
There are 2 different types of 'Vector Duty' motors which are rated for 1000:1 or so speed range. There are TENV (Totally Enclosed Non-Ventilated) and TEBC (Totally Enclosed Blown Cooled).

TENV motors are typically finned Aluminum frame motors, which have enough surface area to dissipate the heat loss, without external air flow. Thus, they can cool themselves without turning.

TEBC motors have a separately powered fan/blower built onto them so the cooling air is the same regardless of the main motor speed.

TENV are typically lower HP, like up to 20 or so, and TEBC go all the way up to 100's of HP.

Fantastic, thanks Gene. It's all about knowing the right key words. All of these motors are around 0.37-0.75kW so we should have no trouble finding a TENV that does what we need.

James Mcquade said:
Since everything else is a powerflex drive, may i suggest that you use the same type of drive and keep the customer happy. nothing new to buy or learn.
james

Thanks James - yes, that's the plan. I'm not sure if the Powerflex 525's do Flux Vector control - the manual says they do SVC (Sensorless Vector Control) and Vector Control (which I would assume is Flux Vector Control?) but I'll check with my rep, and if not, those three motors can get upgraded to a Powerflex 753.

Thanks again for the advice, this forum is a fantastic resource!

GaryS · Mar 28, 2021

Sensorless vector control uses counter EMF to regulate the speed but they will only get down to around 5 to 6 HZ to go below that requires Flux and Vector encoder feedback
i don't know if Powerflex is capable of that or not I would recommend Yaskawa i have used then many times for this type of application

Side note: I just picked up a small project yesterday to replace a stepper motor and drive on the feeder of a large mill
it will be a flux vector drive and motor with encoder i expect the operating range to about 0.5 HZ when milling the need the speed to rock solid end to end.

Servo motor speed control

ASF

Lifetime Supporting Member

g.mccormick

Lifetime Supporting Member

GaryS

Member

ASF

Lifetime Supporting Member

GaryS

Member

Lynx777

Lifetime Supporting Member

jraef

Member

ASF

Lifetime Supporting Member

jdbrandt

Lifetime Supporting Member

Gene Bond

Member

James Mcquade

Member

ASF

Lifetime Supporting Member

GaryS

Member

Similar Topics