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Need help understanding spindle drives etc

macgyver

Stainless
Joined
Aug 2, 2012
Location
Pittsburg, KS
Hey guys I have an old Komo cnc router with a Fanuc OM control. It has multiple spindles and last Friday one quit. I am trying to diagnose which part(s) failed in between jobs so it is going slow.

The spindle that quit is a 7.5 hp Colombo with ER25 collet. It is an 18,000 rpm spindle/motor. The drive that runs it is an AC Tech that puts out 300Hz to get it to 18K.

So, my lack of understanding falls on the drive. I am assuming that it is a vfd, if so, are they more or less all the same? I have never messed with one directly at all, so don't know much. I have seen in other applications, say a manual lathe or drill press you can manually push the up/down buttons to change rpm. I don't know how the drive works in auto mode so that the Fanuc dictates the rpm. As in, any idea as to how the Fanuc and AC Tech talk to each other? If my drive is bad, could I put in an off the shelf vfd of proper hp rating or do I need a special spindle drive?

I haven't found the manual for this one, I have the manual for the 12hp drives which are a different brand.

I am guessing some of my issues are improper use of terminology on my part and others I have talked to over the years...

Thanks for any help,
Jason
 
It could be vfd or dedicated spindle drive, would be easy just google it with the model number to tell what it is.
Control uses 0-10v to control the drive most likely.
Is there an encoder on the spindle?

More info is needed to tell you what it is.

Marko
 
In that era, there were two primary ways for a Fanuc control to control speed on a spindle drive.

One way, and probably how yours is setup, is using an analog voltage. The analog signal is 0-10Vdc where 10V is the maximum RPM and 0V is minimum RPM or stopped. It is also possible to have -10V-0-10V analog command where negative voltages command reverse rotation. There are parameters in the CNC and data used in the ladder that control the relationship of the S address in the program to the analog voltage output level sent to the drive. There are parameters or jumpers on the drive that set the scaling of the analog signal to the output frequency.

The other method uses a digital signal from the CNC to the drive. I've only ever seen that method used with Fanuc drives which is why I doubt your machine uses the digital interface. The digital interface uses 12 bits to command the drive speed. For maximum speed all 12 bits are set to 1 and for minimum speed or stopped all bits are set to 0. Intermediate speeds are set by altering the bits that are on versus off.

The AC Tech drive on my manual mill is made by Lenze.

Lenze in the Americas. As easy as that. - Lenze in the Americas. As easy as that.

I suspect your drive will also be Lenze. I was able to download some documentation for mine when I was installing it.

It is a VFD. in simple terms, a VFD takes the AC power and rectifies it to DC and then with switching transistors, converts the DC voltage back to 3 phase AC at controllable frequency.

In addition to speed control there be some other signals between the CNC and the drive. At a minimum there will be a run command. There could be forward and reverse. There could be enable and e-stop signals. All that is determined by the machine builder so without schematics there is no way for me to tell how your machine is interfaced.

You will have to be sure to buy a replacement drive that can interface the same as the old one. In addition not all inverters will go to 300Hz.
 
Just a follow up even though the original question wasn't about fixing the machine, but about vfd's....

It took me awhile, but I found out it was the cable to the spindle that had went bad. I was getting weird results when I put the meter on either end, so it wasn't clear cut what was going on. Finally failed completely and wasn't getting any power to the spindle.

Wanted to try and hook up a vfd that I had for another machine, but found out it jumps from 60 to 400 Hz with nothing in between, so I expect that wouldn't work.

Ended up confirming both drive and spindle work by running a jumper, so glad it wasn't either of the more expensive parts but pulling 47ft of cable through the machine wasn't fun either.

Thanks for the help,
Jason
 








 
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