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PING: Ned Simmons

Greetings Ned, I don't know yet if using encoders and a servo motor is the best way to go for matching spindle speeds. I have had success doing a bench test using one servo motor as the master and a second servo motor driven by a Gecko 320 as the slave. But the slave is only spinning itself and not the mass of a spindle and chuck. You mentioned using a VFD to match spindle speeds. In the lathe the existing spindle is driven by a DC motor connected to a Randtronics drive. Would both spindles need to be driven by AC motors connected to VFDs in order for speed matching with a VFD to work? And can you suggest any models or brands of VFDs to look at? Thanks, Eric

Reply to
etpm
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From your other posts it sounds like you're making good progress, Eric. Have you run into something about the servo that worries you?

For VFDs, I'd look first at Yaskawa. To get the sort of speed regulation you're looking for you'll need a vector drive with feedback. The F7 and G7 drives, marked "CLV" (closed loop vector) under "Control Type" on this page, accept accessory cards that take encoder feedback. They'll follow step and direction inputs, so should be adaptable to your current control scheme. Unfortunately you have to buy the high-end drives to get the vector option.

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The older Yaskawa GPD drives were also nice units and available with a vector plug-in, though I don't think they had step and direction inputs. You'll also see them rebadged by Magnetek. You may be able to locate one on ebay, though the speed command may be a problem if they don't have the step and direction inputs.

You wouldn't need to have vector drives on both spindles, but that could be a slick setup. Though I've never done it, the Yaskawas can be networked, and I believe can be set up as slave and master.

I expect Mitsubishi has something as well, but I'm not as familiar with their current models. It also appears you can get a vector drive from Automation Direct that accepts step and direction, undoubtedly cheaper than Mitsu or Yaskawa.

Reply to
Ned Simmons

Thanks Ned. Even though things are working well now it will eventually involve two motors on the second spindle. Since the servo will be belt driving the spindle, and there will be the load of the spindle and chuck, I am a little concerned. The next test will be to load the slave and see if it keeps up. I still need to make a strobe to watch setup. Eric

Reply to
etpm

Oh yeah, I'd forgotten about the 2-motor setup.

If you can get your hands on a large brushless servo motor cheaply, it's possible to use it as a synchronous motor and drive it open open loop with a conventional volts/Hz VFD. It'll lock to the drive's output frequency without the slip inherent in a typical induction motor, so commutation and shaft speed feedback are unnecessary. Probably more unconventional than what you've got in mind, but I'll explain more if you're interested.

Reply to
Ned Simmons

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