C-Axis Homing to Spindle Encoder Pulse

[roundel325]

I'm dreaming of implementing a c-axis on my lathe. I have parts on hand to do a DMM Servo --> strain wave gear reduction --> electromagnetic clutch --> timing belt --> spindle. The clutch will decouple the c-axis drive (and its encoder) during turning ops, so to orient the part for c-axis machining I will need to to home to a marker on the spindle. Can Acorn/CNC12 support homing to the spindle encoder index pulse in the same way I now home my X and Z axes to their respective servo encoder pulses via ZRI inputs?

Thank you for any insight.

[cnckeith]

yes, its just like any other axis in regards to Zri homing.

[roundel325]

Ok. That is not the answer I was expecting. I'm talking about detecting the index pulse of the spindle encoder connected to the Acorn DB9 port, not a ZRI from a servo driver. What Acorn input do I need to monitor to see the DB9 index pulse?

[martyscncgarage]

Ok. That is not the answer I was expecting. I'm talking about detecting the index pulse of the spindle encoder connected to the Acorn DB9 port, not a ZRI from a servo driver. What Acorn input do I need to monitor to see the DB9 index pulse?

The spindle Encoder port on Acorn is for just that. Speed input and the index pulse for threading/tapping. Not used for positioning.

If you are trying to use a DMM DYN4 Servo drive for BOTH spindle and Positioning, they have special firmware you have to ask for at the time you ordered the drive. You have to follow their schematics. So far, and I continue to ask, I know of no one successfully implementing a DYN4 and Servo motor as a spindle drive, let alone a C axis. It sounded like you were going to kick in the Servo motor when you wanted C axis and leave a standard 3 phase AC motor and VFD control the spindle....

[roundel325]

Ok. That is not the answer I was expecting. I'm talking about detecting the index pulse of the spindle encoder connected to the Acorn DB9 port, not a ZRI from a servo driver. What Acorn input do I need to monitor to see the DB9 index pulse?

It sounded like you were going to kick in the Servo motor when you wanted C axis and leave a standard 3 phase AC motor and VFD control the spindle....

That is exactly what I am wanting to do. I was hoping to be able to home the c-axis to the spindle encoder index pulse because I have a few parts to make that require a c-axis machining op, then turning op, then another c-axis op. Since the c-axis servo would be clutched out during turning ops, this is only possible if the c-axis can be re-homed to the spindle position after the turning op. Otherwise the control wouldn't know how the part is oriented.

Unless someone chimes in otherwise, I'll take it that the answer is "It can't be done." and try to constrain my designs such that the c-axis machining can be accomplished in one chunk without any turning ops interspersed.

Thanks!

[martyscncgarage]

Why couldn't you use the index pulse from the C axis Dyn4 as an input to Acorn to home that servo.

Perhaps Marc Leonard will chime in, to see if there is a way to do it.

[tblough]

Marty,

When the C-axis is unclutched from the spindle, it's encoder looses it's position reference relative to the part in the spindle. In order for this to work, the C-axis needs to home based on a signal that maintains relation regardless of the clutch state. i.e. the index pulse from the encoder that's always connected to the spindle.

[martyscncgarage]

Marty,

When the C-axis is unclutched from the spindle, it's encoder looses it's position reference relative to the part in the spindle. In order for this to work, the C-axis needs to home based on a signal that maintains relation regardless of the clutch state. i.e. the index pulse from the encoder that's always connected to the spindle.

Thanks for the clarification Tom.
Marc would be the one to say whether or not that could be done....I'm not so sure.

[Caleb]

Why not have some sort of positive engagement drive dog the will only engage in one place rather than a clutch?

[roundel325]

I'd prefer to buy something off the shelf rather than a scratch build. The whole mechanism would have to spin so I'm not sure how it could be wired. And it would need to have no backlash. Do you know of such a thing available to fit motor shafts?