[ZeroBacklash]

Again if you need positioning then a servo would be best option. Most servos will output near 100% torque at 0 RPM with a pretty flat torque curve through the RPM range.

How about a Automation Direct VFD GS3 series with encoder connected to a 3phase motor. Will this give sufficient accuracy to do position control?
My torque requirements are minimum 100Nm.
Unfortunately DMM servo's are not meeting that They have max torque of around 12Nm.

[Jim Dawson]

How about a Automation Direct VFD GS3 series with encoder connected to a 3phase motor. Will this give sufficient accuracy to do position control?
My torque requirements are minimum 100Nm.
Unfortunately DMM servo's are not meeting that They have max torque of around 12Nm.

Unfortunately no, I have a GS3 and encoder on the 7KW spindle motor on my lathe. I thought I might be able to get it to position, but the GS3 is just too ''loose'' to make that work, I played with it for days trying to make it work. When I can find one at my price, I'm going to replace the spindle motor with a 10KW servo.

Since you only need 10 rpm, a 10:1 gearbox would give you 120Nm, to be really safe go with a 15:1 gearbox and you would have 180Nm available.

[ZeroBacklash]

Unfortunately no, I have a GS3 and encoder on the 7KW spindle motor on my lathe. I thought I might be able to get it to position, but the GS3 is just too ''loose'' to make that work, I played with it for days trying to make it work. When I can find one at my price, I'm going to replace the spindle motor with a 10KW servo.

Since you only need 10 rpm, a 10:1 gearbox would give you 120Nm, to be really safe go with a 15:1 gearbox and you would have 180Nm available.

Now thats a dampener. I mean regarding the VFD. I was planning to use an 8 pole 3ph motor (already low on rpm) with a VFD and encoder and with the GS3 drive I thought I would get sufficient accuracy to do position control.

Is threre no way to use a 3 ph AC motor with VFD and get sufficient accuracy for spindle operations with position control even with a high resolution encoder?. How much accuracy were you getting from your system.?

[Jim Dawson]

Now thats a dampener. I mean regarding the VFD. I was planning to use an 8 pole 3ph motor (already low on rpm) with a VFD and encoder and with the GS3 drive I thought I would get sufficient accuracy to do position control.

Is threre no way to use a 3 ph AC motor with VFD and get sufficient accuracy for spindle operations with position control even with a high resolution encoder?. How much accuracy were you getting from your system.?

I am not able to position at all. I am using a Galil motion controller so I have a lot of control over the way the system reacts. Thus far, no matter what settings I use in the drive or in the motion controller I can not control any positioning move. I can make it run at a constant speed or even programmatically vary the speed from about 5 to 5500 RPM and it's rock solid at any set speed. But any time I adjust any PID parameter above zero I lose control, I tried every trick I know and I've been doing this for about 25 years. The drive just does not react to speed change commands fast enough to act as a servo positioning system.

One thing I have thought about doing is adding a DMM servo to the spindle drive to use for low speed positioning for mill/turn functions and add a electro-mechanical system to clutch it in when needed, that is one way I've see it done. I have 1.8KW DMM servos on the axes, live tooling drive, and turret drive. Been very happy with them. But what I will probably do is just install a 10KW servo motor and be done with the problem.

In your case, a servo with low backlash gearbox would be the ideal setup. Low RPM and positioning resolution in fractions of an arc second.

[ZeroBacklash]

I am not able to position at all. I am using a Galil motion controller so I have a lot of control over the way the system reacts. Thus far, no matter what settings I use in the drive or in the motion controller I can not control any positioning move. I can make it run at a constant speed or even programmatically vary the speed from about 5 to 5500 RPM and it's rock solid at any set speed. But any time I adjust any PID parameter above zero I lose control, I tried every trick I know and I've been doing this for about 25 years. The drive just does not react to speed change commands fast enough to act as a servo positioning system.

One thing I have thought about doing is adding a DMM servo to the spindle drive to use for low speed positioning for mill/turn functions and add a electro-mechanical system to clutch it in when needed, that is one way I've see it done. I have 1.8KW DMM servos on the axes, live tooling drive, and turret drive. Been very happy with them. But what I will probably do is just install a 10KW servo motor and be done with the problem.

In your case, a servo with low backlash gearbox would be the ideal setup. Low RPM and positioning resolution in fractions of an arc second.

I'm trying to do something like this

https://www.youtube.com/watch?v=XAy-nWMypvk

And the vfd would be connected to the spindle drive. If you skip to 3 minutes into the video it will show you winding on a cylinder with dome shaped ends and you can notice how the spindle slows down slightly to allow for winding on the ends. So will this be achievable on a VFD and 3ph ac motor?

[Jim Dawson]

I'm trying to do something like this And the vfd would be connected to the spindle drive. If you skip to 3 minutes into the video it will show you winding on a cylinder with dome shaped ends and you can notice how the spindle slows down slightly to allow for winding on the ends. So will this be achievable on a VFD and 3ph ac motor?

Yes, that is doable. You would need to electronically gear the axes to the spindle with an encoder on the spindle. The ability to use electronic gearing would depend on what motion controller you are using, I don't know if all of them have it available. Looks like that winder would need some kind of custom software written to coordinate the motions, but it might be possible with standard CNC G code, maybe something like a rigid tapping routine.

[ZeroBacklash]

Yes, that is doable. You would need to electronically gear the axes to the spindle with an encoder on the spindle. The ability to use electronic gearing would depend on what motion controller you are using, I don't know if all of them have it available. Looks like that winder would need some kind of custom software written to coordinate the motions, but it might be possible with standard CNC G code, maybe something like a rigid tapping routine.

Ok thanks. I don't understand the electronic gearing part but will look it up. So do you still think that a servo would be best for this application for the spindle or a VFD is equally well suited to do the job? I mean if I use a VFD I would I get the position control for co-ordinated motion of the axis?