Let's say someone who should have known better...

[RetiQlum2]

...swore up and down that a couple of VFDs in use on one line were servos and I believed him.

How do I use Kinetix servos to drive a web-type product as if they were VFDs? It's way too late to change horses now.

More detail: I am driving asphalt roofing material. It's a backing of fiberglass or polymer weave that is impregnated and coated with asphalt, polymers, films, sand, and rock. The process is similar to a large, smelly, black, printing press. This is near the end, feeding into a winder. Previously there were two VFD/motors that dropped a big loop into a pit for the next section to pull. The motors shut down when a low photo eye is broken and turn on again when a high photoeye is cleared. I now have servos there.

 

[OkiePC]

Is there still a slack loop is downstream of the servo motors you are concerned about?
And if so, the winder is downstream of the slack loop?

Generally, as long as they're sized right, having the extra duty cycle and precision capabilities of servos when you don't really need them is better than the reverse.

 

[robertmee]

...swore up and down that a couple of VFDs in use on one line were servos and I believed him.

How do I use Kinetix servos to drive a web-type product as if they were VFDs? It's way too late to change horses now.

More detail: I am driving asphalt roofing material. It's a backing of fiberglass or polymer weave that is impregnated and coated with asphalt, polymers, films, sand, and rock. The process is similar to a large, smelly, black, printing press. This is near the end, feeding into a winder. Previously there were two VFD/motors that dropped a big loop into a pit for the next section to pull. The motors shut down when a low photo eye is broken and turn on again when a high photoeye is cleared. I now have servos there.

Which plant? I've been in just about all of them.

The winder pit, loop is a common application on commercial roll lines. As Okie said, servo should be as or more capable than a standard VFD. On kinetix, just enable the axis and use MAJ and MAS commands to mimic the start/stop of a VFD.

There will be a bit more housekeeping to monitor axis, reset after faults, etc, but once set up it'll work flawlessly

 

[robertmee]

Is there still a slack loop is downstream of the servo motors you are concerned about?
And if so, the winder is downstream of the slack loop?

Generally, as long as they're sized right, having the extra duty cycle and precision capabilities of servos when you don't really need them is better than the reverse.

Yeah, winder would be downstream of pit. There's an FPL (finished product looper) which is just a big chain accumulator that runs line speed with material festooned in it, a pull roll after that feeds this pit, then the winder. The pull roll will feed material into the pit for the winder. Some use pits, some use shock rolls, some free loops with the winder in the air, but it's all the same principle.

 

[joseph_e2]

If you want to get fancy.....

At my last place, we had 2 bonding mills with flatteners just prior to belt sanders. The flatteners were VFD driven with their speed reference coming from a tach generator on the main mill motor. They got a speed trim from a potentiometer that measured the angle of a dancer arm that rode on the strip at the exit of the flattener. Once tuned (and as long as the pot didn't slip on the shaft - war story for another day), the VFD would run at constant speed to maintain a constant loop height.

If you wanted, you could do something similar. Otherwise, I was thinking along the same lines as @robertmee with MAJ/MAS instructions.

Honestly, if your line speed stays within a relatively narrow window, you might even get away with an across-the-line starter in a pinch, but that's harder on the motor. You would need to consider the motor service factor and almost certainly have an externally powered cooling fan. Since you have the VFD/servo drive, it makes sense to use them.

 

[kekrahulik]

I somewhat agree with the "just use MAJ/MAS instructions" for run/stop. The other critical thing you might need is MCD.

The MAJ instruction tell the servo to run at a certain velocity and acceleration. It is is a "one time instruction" in the sense that it gives the servo the command to run, the speed, and accel all at the moment when the MAJ is triggered. The servo will run with those values until you tell it to do something else. So if you want to change speed, you must issue a new command. The MCD (Motion Change Dynamics) tell the servo to change the velocity or accel. So if the motor speed needs to vary (ie if the line speed changes or if it has loadcell or dancer feedback altering the speed), then you will need to constantly trigger new MCD commands.

If your current VFD's are running in torque control, the servo application becomes more challenging. It can be done, but servos are very velocity and position focused, so you need to play some games to run a servo in a torque mode and not have it fault for position or velocity errors.

 

[GaryS]

I just wanted to say that VFD’s are replacing servo all the time. I have done many myself
the same or better provenance at a much better price
in your application .I would replace the servo’s with Flux Vector VFD’s and end the problems

 

[RetiQlum2]

I just wanted to say that VFD’s are replacing servo all the time. I have done many myself
the same or better provenance at a much better price
in your application .I would replace the servo’s with Flux Vector VFD’s and end the problems

It is far too late for that.

If you want to get fancy.....

At my last place, we had 2 bonding mills with flatteners just prior to belt sanders. The flatteners were VFD driven with their speed reference coming from a tach generator on the main mill motor. They got a speed trim from a potentiometer that measured the angle of a dancer arm that rode on the strip at the exit of the flattener. Once tuned (and as long as the pot didn't slip on the shaft - war story for another day), the VFD would run at constant speed to maintain a constant loop height.

If you wanted, you could do something similar. Otherwise, I was thinking along the same lines as @robertmee with MAJ/MAS instructions.

Honestly, if your line speed stays within a relatively narrow window, you might even get away with an across-the-line starter in a pinch, but that's harder on the motor. You would need to consider the motor service factor and almost certainly have an externally powered cooling fan. Since you have the VFD/servo drive, it makes sense to use them.

"across-the-line starter"

I've never heard that term before. What does it mean?

I think the MAS, MAJ, and MCD is the way to go, at least at this point. I might see something else later, and I'll have the capability. You know, due to spending an extra 50k on servos.

 

[lmscar12]

"across-the-line starter"

I've never heard that term before. What does it mean?

A starter that provides no speed control or ramping. "Across-the-line" meaning it simply applies the full line voltage and frequency directly to the motor, i.e. FVNR.

 

[alan_505]

Another term is DOL, Direct On Line, by using a contactor to power the motor directly with the supply voltage.