[solved] Rehoming Lathespidle / Rotary-Axis from inside GCode

switching between Mesa stepgen and the electronic spindle pot works fine. I can jog as rotary and as soon as I issue a spindle enable I can control the servomotor in speed mode using the analog input as soon a spindle is disabled I'm back to the stepgen and position control in the servo controller.
The problem is the encoder position changes when using the servo in speed mode which gets it out of sync to the joint motor position-fb. Hence the idea to orient the spindle to match the motor position-fb value before switching back to position mode.

I see, thanks.

I guess there's a subtlety in the sequencing variations, and I don't know which is 'better' or if it makes any difference:

• Scheme #1
  • C-axis homes to encoder index on enable/home
    • run some positioning moves
  • Switch to velocity mode
    • control method doesn't matter (analog or step/dir or pwm)
    • run spindle in velocity mode
  • Encoder is now out of sync with last axis position command
  • Switch to axis mode
    • reset encoder index
    • home C-axis
• Scheme #2
  • Same as above but instead of resetting the encoder index
  • Orient spindle before switching to axis mode (using orient.comp)
  • Switch to C-axis mode
    • no need to home axis?

I'm sure I'm missing something, but I wonder if orient will work well enough as the hand-off between a velocity mode and positioning mode?  I'd be concerned that the orient tolerance wouldn't match the axis following error tolerance, and you'd have to set the joint ferror tolerance high enough that subsequence axis-spindle-axis mode changes would result in misalignment between the two axis mode changes.

There (probably) wouldn't be an error accumulation over multiple axis-spindle-axis mode changes, but I fear using orient wouldn't nail the position each time the axis mode is enabled.

I would think that the encoder reset plus a forced C-axis homing to index at each positioning-mode enable would be the most accurate method?  That seems to be the scheme used in caxis.comp, and is also the method used on my Fanuc thing.

 

I agree that homing the rotary at each switch to positioning mode seems the most sensible approach. I'll need to have a closer look at the caxis.comp.

The caxis.com looking always with lathe eyes. What happens if you have a milling machine with toolspindle and A or C axis and want turning? Then we have two spindles and the story begins new. I think first step should be teaching lincnc that round axis only count max. 360° and second step supported rehoming. But i take a look in the homing.c and closed it. Behind my mind...
What do think about this idea? And is there someone who can do it?

chris@cnc wrote:

The caxis.com looking always with lathe eyes. What happens if you have a milling machine with toolspindle and A or C axis and want turning? Then we have two spindles and the story begins new. I think first step should be teaching lincnc that round axis only count max. 360° and second step supported rehoming. But i take a look in the homing.c and closed it. Behind my mind...
What do think about this idea? And is there someone who can do it?

The lines get blurry between a mill-turn or a turn-mill, don't they?  

I haven't done this, but I believe controlling two spindles can be done in LCNC using spindle.1 for the 2nd spindle motor.  Main spindle would be spindle.0.

So you set up the A-axis with a position-mode PID and a second PID connected to spindle.1.  Switch between them, just like we've been discussing for C-axis lathe stuff in this thread.  Could probably recycle the caxis.comp as 'aaxis_spindle.comp' with some minor editing.

LCNC is already capable of treating a rotary axis as only having 0-359.999 degrees.  See the [AXIS] section of the INI file help document.

Regarding A-axis homing/rehoming:
My mill has an A-axis driven by a servo, open-loop to LCNC.  I'm using the drive's internal home-to-index function through a couple of IO pins:

• LCNC->Drive
  • start homing
• Drive->LCNC
  • homing complete
  • alarm

My particular drive doesn't require an 'unhome' signal before homing a second (or more) time. So my "Home-A"​ button (macro) outputs:

• halui.joint.3.unhome (unhomes A)
• (slight pause)
• halui.joint.3.home (LCNC immediately sets DRO to 0.000)
• start homing (via motion.digital-out)
• wait for homing complete (via motion.digital-in)
  • if complete w/in time permitted - macro is done
  • if fails to get complete signal
    • alarm
    • unhome joint

All the usual homing data is pre-programmed in the drive (homing speed, index search speed, encoder offset)

The normal LCNC X/Y/Z homing function omits the A-axis entirely; I usually have a trunnion table on the A-axis and I don't always have 360 clearance if there's a long tool in the spindle.  Having a separate HOME-A button helps me remember to check for interference.

Point is, you can home/unhome any joint you want via gcode in a macro.  i.e. the same macro that switches between axis-position mode and spindle-velocity mode can unhome the axis each time its run.  And it's not limited to lathe main spindles.

Unless I misunderstood something, ​​​​​​I think all of your questions/comments are already addressed - or at least manageable - in LCNC.

spumco wrote:

LCNC is already capable of treating a rotary axis as only having 0-359.999 degrees.  See the [AXIS] section of the INI file help document.

Thanks for this hint. I see now the option "WRAPPED_ROTARY = 1"

spumco wrote:

Regarding A-axis homing/rehoming:
My mill has an A-axis driven by a servo, open-loop to LCNC. I'm using the drive's internal home-to-index function through a couple of IO pins:
LCNC->Drive
start homing
Drive->LCNC
homing complete
alarm
My particular drive doesn't require an 'unhome' signal before homing a second (or more) time. So my "Home-A"​ button (macro) outputs:
halui.joint.3.unhome (unhomes A)
(slight pause)
halui.joint.3.home (LCNC immediately sets DRO to 0.000)
start homing (via motion.digital-out)
wait for homing complete (via motion.digital-in)
if complete w/in time permitted - macro is done
if fails to get complete signal
alarm
unhome joint

The Same should be possible on a lathe c axis. The "drive-index signal" can touch the halui.joint.3.home and hm2***encoder.reset and then switch axis to closed loop and joint mode.
It doesn't matter which machine or axis we're working on.
It seems I won at my workshop next weekend. Let's see what the big boss say about it...