Ho do I add extra motor & VFD to increase torque at low speeds.

[greeder88]

I have a cnc milling machine spindle with not enough HP at low speeds. I have a 5hp ac motor and a Mitsubishi FR-V220E Vector inverter with encoder and index card installed. Due to cost I can't buy a bigger motor and inverter.

I will mechanically add (In the timing belt loop) my spare motor and inverter to get 10hp. I don't have a spare index card for the second inverter (Used to align the spindle at stop for tool changer). I do have a motor, inverter, and encoder kept as spare parts.

Searching on the internet I see that this can be done by feeding analog out to analog in. My problem is how exactly to wire this. I am sure it is not just run wires across to the second motor and I'm done.

Any help on how to wire would be appreciated.

Here is a link to the inverter manual:
http://suport.siriustrading.ro/02.D...Instruction Manual IB(NA)-66658-D (07.98).PDF

Thanks,
George

 

[greeder88]

Here is a link that vaguely describes how to do it but not enough details to get it done.

http://www.controldesign.com/articles/2002/235.html

 

[Jraef]

I've done it several times and my experience is that it's hit and miss. I did it first with two drives from a company called PDL from New Zealand. Their engineers insisted that it could only be done with encoders on each motor and by tieing the DC buses together. It worked, but it was a royal pain in the rear end and I would NOT recommend that method to anyone. Since then I learned from someone else that Siemens Sinamics G120 and G150 drives could do it with analog communications. It works OK, load sharing is within 1% at any given moment and that was good enough for my applications. But I wasn't doing machine tools with that, I was doing twin 400HP rock crusher motors and a 1% share scenario was plenty good enough for me.

The principle is the same however. Pick one drive as a master, run it in speed follower mode and program the analog output of that drive to be motor shaft torque. make sure your drive has that option, it won't work otherwise. Then on the slave, set the VFD up to be a torque follower using the analog output from the master and the torque command signal to the analog input in the slave. You will need for the slave to at least have Open Loop Vector control for that to work though, and that manual was taking way too long to download for me to bother with it.