Synchronizing speed between two or more Vector AC Freq drives.

[VinceS]

I have an upcoming project which will replace the existing open loop single motor mechanical belt driven system with two closed loop VFD's. The existing system is subject to belt slip which causes speed matching issues between driven arbors. The project calls for using vector mode VFD's driving each arbor using a shared TAC speed input to both drives. Over all this seems a simple closed loop system.

My concern is precise speed control between the two VFD's. I am also concerned about the use of a single TAC as a speed input to feed both VFD's as each exists in a separate portion of the system. I would appreciate any thoughts, suggestions, or lessons learned regarding speed-matching of multiple drives.

 

[Jraef]

Are the arbors mechanically linked or separate? Seems odd if they are separate. Why do they need to be the exact same speed?

That's not to say it can't be done, it can. Look for closed loop vector VFDs that provide a feature called "electronic line shaft" (a.k.a. "electronic gearing") capability. That means they can be used in machines, such as printing presses and other web based systems, to replace a solid drive shaft that use to be the only way to do this. This kind of feature is usually only found in the top of the line vector drives from major manufacturers, and is often associated with drives capable of "motion control" applications as well, because it involves very high speed signal processing. Examples (not endorsements) would be Yaskawa G7, ABB ACS800, Siemens Simotion S120 etc.

But one thing I would challenge is what you mean by "TAC". If by that you mean an analog tachometer, you may not like the performance. They are notoriously "sloppy" for an application like this. I would use an incremental encoder, sometimes called a digital tachometer, with as many pulses per revolution as possible. Pick out a good one, because cheap buys you trouble on a critical mission like this. Avtron is probably the best..

 

[weressl]

I have an upcoming project which will replace the existing open loop single motor mechanical belt driven system with two closed loop VFD's. The existing system is subject to belt slip which causes speed matching issues between driven arbors. The project calls for using vector mode VFD's driving each arbor using a shared TAC speed input to both drives. Over all this seems a simple closed loop system.

My concern is precise speed control between the two VFD's. I am also concerned about the use of a single TAC as a speed input to feed both VFD's as each exists in a separate portion of the system. I would appreciate any thoughts, suggestions, or lessons learned regarding speed-matching of multiple drives.

Do yourself a favor and simplify your life, use a single ASD with synchronous belt drive.

http://www.dodge-pt.com/products/pt_components/sprockets_drives/sprockets_drives.html
http://www.dodge-pt.com/products/pt_components/belts/belts.html

 

[petersonra]

Do yourself a favor and simplify your life, use a single ASD with synchronous belt drive.

http://www.dodge-pt.com/products/pt_components/sprockets_drives/sprockets_drives.html
http://www.dodge-pt.com/products/pt_components/belts/belts.html

I did some electronic gearing projects a few years back that had as many as 6 separate axis slaved to one master motor. They worked very well. Just regular old AC motors. Even did a couple that used DC motors.

So much simpler especially since the gear ratios had to vary depending on what product was being run.

 

[Besoeker]

I have an upcoming project which will replace the existing open loop single motor mechanical belt driven system with two closed loop VFD's. The existing system is subject to belt slip which causes speed matching issues between driven arbors. The project calls for using vector mode VFD's driving each arbor using a shared TAC speed input to both drives. Over all this seems a simple closed loop system.

My concern is precise speed control between the two VFD's. I am also concerned about the use of a single TAC as a speed input to feed both VFD's as each exists in a separate portion of the system. I would appreciate any thoughts, suggestions, or lessons learned regarding speed-matching of multiple drives.

Single TAC? Is that speed demand or speed feedback?

If the two drives are mechanically coupled as your post suggests, then trying to operate both in independent speed control probably isn't the best way to go. A master-slave arrangement to ensure load sharing might be better.

 

[VinceS]

Follow-up info...

Follow-up info...

Each arbor is driving a separate belt. The belts convey cartons being folded, on an old, European MFR, folding carton machine. The current main motor provides motion to various arbors via a 6 inch flat belt.

I have considered using a chain or synchronous belt, which also eliminates the original issue of the flat belt slipping. This is most likely the most cost effective solution.

Speed demand will be via a digital input which can reutilize existing control. The speed feedback would be obtained from a TAC, or as suggested a incremental encoder.

Thanks for the input on the electronic gearing, this may be what's require.