VFD Selection for Rigid Tapping

I have converted a Fadal 3016L and i'm happy with the outcome, minus one issue, the VFD. I have a Hitachi WJ200 VFD that is only capable of a minimum frequency of .5 hz (20 RPM). My goal is rigid tapping. Any help would be appreciated to either get this VFD to rigid tap or select another VFD or drive that will reliably rigid tap.

Chris

What's the issue with it?  Are you trying to tap at 20rpm?

I have a WJ200 that rigid taps just fine in a non-LCNC application.  I split the motor encoder differential signal between the controller and the VFD since the WJ200 can only take single-ended signals.

The VFD is set to feedback mode and the controller does not run a PID loop - so there's no fighting between the controller and VFD.  The controller just receives the encoder signals and makes the Z-axis follow the spindle.

The specification listed in my manual state "0.1 to 400Hz" output frequency range.  In Sensorless Vector mode it can output "200% torque at 0.5Hz"  and maybe that statement misled you?  

In feedback mode the WJ200 can operate at pretty close to 0rpm.

The WJ200 is nice in that there's no additional (expensive) feedback card required to accept incremental encoder signals.  The downside is that the encoder inputs can only handle something like 2khz in A-quad-B mode (bi-directional).  To compensate for this you can use a fairly low count encoder ( think I used a 100-line, 400-count) encoder if you plan to tap at high rpm.

The real trick is if you've got the Fadal 2-speed pozi-drive system.  I'm pretty sure those don't have encoders directly on the spindle, and neither ratio is a convenient 1:1.  But that problem has nothing to do with the VFD.

Thank you for the help. I have a 1:1 wye/delta spindle and the encoder and index are setup and working as they should. I have 4000 counts per rev quad encoder.

There's a heck of a lot of settings pertaining to Pulse Train setup. Any further direction you can give would be appreciated. I'm controlling it currently with a 7i77 analog 0-10 volts using a wj200 input from linuxcnc to tell it to turn CW or CCW.

• First suggestion is to try running the WJ200 open loop: send the encoder signal to LCNC and see how it works.  The VFD doesn't need encoder signals to rigid tap fairly well, even at low speeds.  LCNC will simply read the encoder and command the Z-axis to follow the spindle, even if the VFD is turning the spindle at non-constant speeds.
• If that doesn't work well, next suggestion is to tune up the VFD a bit.
  • Run the auto-tune and save settings.
  • Parameters I changed to 'hot-rod' my spindle motor (2hp Marathon BlackMax)
    • A041 - 01 (automatic torque boost)
    • A044 - 03 (sensorless vector)
    • A054 - 75% (DC braking force for decel)
    • A059 - 10 (carrier frequency during DC braking, for some reason I could hear it at the default setting of 5khz)
    • Set your accel/decel fairly aggressive and test it.  If it trips due to overvolt, back it off a bit.  This will help with rigid tapping over-run in blind holes.
      • I'm sure you've got a braking resistor already...but if not you really want one.  The VFD can stop a spindle stupid fast if it's got a place to dump the energy.  I had 1-second ramps up and down to 8kRPM.
• If you want to run the VFD closed loop:
  • P003 - 01 (encoder feedback)
  • P004 - 02 (2-phase pulse, connect to terminals EA & EB)
  • P011 - depends on your encoder

If you do set it up closed loop you can test if the encoder is functioning by entering the simple positioning features and command it to home.

I just got it sorted out and i'm tapping without encoder feedback to the VFD. Seems to be working very well between 200 and 500 rpm's. I will try your "HOT ROD" settings and see if i can improve accel/decel. Yes it has the original Fadal braking resistor and works pretty well.

Thanks for taking the time to help. It's much appreciated.

Good to hear.

One parting thought... I found a old note to myself in my VFD settings spreadsheet.  Seems I set the decel curve to linear (trapezoidal) instead of S-curve.  I think I gained a tidbit of decel speed (probably half a second) by changing the curve.  Accel remained S-curve (default).

 

Noted. One thing i like about leaving the mill in sensorless vector for low speed tapping is the gobs of torque it has at low speed.

10HP spindle motor

COlger81 wrote:

Noted. One thing i like about leaving the mill in sensorless vector for low speed tapping is the gobs of torque it has at low speed.

10HP spindle motor
 

Oh yes indeed.  I've got a buddy with two Fadal 6030's and in low range the 20hp Baldor will destroy stuff.  Definately not 'Haaspower'.

An old K&T trick was to tap in the next higher gear than for milling.
This cuts accel and decel times. Torque should not be a problem.
They called it extended tap range.