Hi,
He wishes to drive the threading leadscrew with a closed loop stepper motor rather than gearing it physically to the spindle.
Yes, that could indeed be OPs intention.
If the index signal from the spindle encoder is hooked to the PMDX-416 and in turn to Mach then Mach has continuously updated
value of spindle speed. A small script in the PLC would allow the leadscrew stepper to be driven as a velocity jogged out-of-band axis.
The result would be that the leadscrew attains and maintains a speed in direct proportion to the spindle.
Note this approach is still not the same as a gearbox. The leadscrew would be velocity synchronized to the spindle but exact
posistional synchronization could not be assured.
If an index pulse is received by the PMDX-416 it will be transmitted to Mach, but there will be an indeterminate delay of several
or maybe tens of milliseconds. Mach will then do its calculation and issue P(osition)V(elocity) over T(ime) moves to the PMDX-416
with another indeterminate delay. The communication delays prevent the leadscrew stepper from maintaining exact positional
synchronization.
Exact positional synchronization can be achieved ONLY if the communication delays can be eliminated. When a G76 threading command
is encountered while Mach supervises actually the PMDX-416 takes over and does the synchronization itself without relying
on Mach with the inherent comm delays.
This could also be done with an Arduino, it would monitor the spindle encoder and produce step/direction pulses to the stepper
driver. That could be done continuously and within microseconds and positional synchronization could be attained.
Craig
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