Spindle Step/Dir and as C axis one the same Servo

I'm not sure I understand, the stepgen position feedback
should not be connected to anything when in spindle mode.

PCW wrote:

I'm not sure I understand, the stepgen position feedback
should not be connected to anything when in spindle mode.

Stepgen has two connections. To Spidnle and Axis. That's why it has both feedbacks: velocity-fb and position-fb.
 

position feedback must be unconnected in spindle mode

PCW wrote:

position feedback must be unconnected in spindle mode

That would be ideal. And how should I do that?

in spindle mode, the stepgen velocity command comes directly from
the (perhaps scaled) spindle velocity. The stepgen feedback position
would be ignored in spindle mode. The joint feedback could be looped
back from the C joint commanded position this case. Finally, a homing
to index move would be done to re-synchronize the spindle position to
absolute C coordinates.

PCW wrote:

The joint feedback could be looped
back from the C joint commanded position this case. Finally, a homing
to index move would be done to re-synchronize the spindle position to
absolute C coordinates.

The question is how? As I understand there is no command like UNlink signal with pin.
I cannot use mux2 to switch source of pos-fb (that was my first idea), because if I have position-fb = 300 in stepgen AND joint AND pid, and then somehow stepgen position-fb became 0.0 (or source of this value became 0.0 and joint/pid have 300) -> joint error occur.

 

One mux2 would be the one that selects the stepgen velocity command to come from
the PID output or the scaled spindle speed command.

The other mux2 would select the joint feedback from either the stepgen feedback
or the joint position command.

The trick is not to switch the second mux back to stepgen feedback until
the joint command and stepgen feedback are zeroed (ideally by
homing to index)