The Yaskawa servos, at least, have the commutation information in the third (index) encoder track. The advantages/reasons for this are no hall sensors needed and less conductors needed back to the drive.
The Z track on these motors is not a single pulse once per turn, but instead a square wave with varying duty cycle and phase (compared to the A track). After looking at this signal with an oscilloscope I think the duty cycle varies in fixed steps of 25, 50 and 75 percent, and the phase also in fixed steps (pi/2?). It should not be impossible to figure this out and build a converter to normal hall signals, if one really wanted to.
Arvid |