Would like to learn about index enable hoohah

Hello all,

Hal signal flow is making much more sense to me nowadays

But I still have some learning to do in that I'm a bit lost by the index carry on - I've tried reading the relevant manual pages but I think I'm up against a wall of personal ignorance to the topic...

Ok so:

hostmot manual says:
(bit in/out) index-enable: When this pin is set to True, the count (and therefore also position) are reset to zero on the next Index (Phase-Z) pulse. At the same time, index-enable is reset to zero to indicate that the pulse has occurred.

Hal PID page says:
pid.N.index-enable bit in
On the falling edge of index-enable, pid does not update the internal command derivative estimate. On systems which use the encoder index pulse, this pin should be connected to the index-enable signal. When this is not done, and FF1 is nonzero, a step change in the input command causes a single-cycle spike in the PID output.

Axis / Motion page says:
axis.N.index-enable IO BIT - Should be attached to the index-enable pin of the joint’s encoder to enable homing to index pulse

See! I did read the manual

I know at least 3 of the 5 motors I'm using have index from their encoders - I think i know what they can do, but not so much of the use of them practically, as in great we know when the motor has gone around once, but if we have encoder pulses then we know that already ? hmmmm, thinking cap on - ok so for homing maybe ? like you get a trigger from a physical home switch then drive until you hit the index signal ?? (better accuracy?) - but I don't quite get what is going on with the Hal here

We have a wire called ' x-index-enable' it connects the three hal whatsits above (correct?) - but which if any will actually go 'high' ?

- hm2_5i22.0.encoder.01.index-enable ? every rotation ??
- axis.N.index-enable ?

I'm a bit flummoxed of where to go looking for info next - can anyone enlighten me ?

cheers all,
Nick

multi-pass tapping ... hmmm, deep blind holes - swarf breaking/clearing ? or use a spiral flute ? anyways ...

ok, I can see why and how knowing the real shaft position with respect to the encoder '0' is helpful. Lathe threading for example, the index effectively becomes the thread and spring loaded thread follower on manual feed lathe in threading mode (?). But with an encoder once you've homed once aren't you set, counts will maintain positioning right ? or is it helpful for the fact you might not do all your work in one session, so you want absolute shaft positioning for every session after an evening switch on/switch off and re-home ?

When you say a function sets index-enable for a specific encoder - you mean it sets "axis.N.index-enable" ? Any example functions ?

What I'm hearing is that I could remove this part if I were just doing vanilla machining (i.e. didn't have a servo spindle and weren't coding anything that would call those functions) ? Or in the case of a 3 axis, just have it on the Z axis ?

Also just to confirm - does this line do the same thing in hal as the above code:

net x-index-enable hm2_5i22.0.encoder.01.index-enable <=> axis.0.index-enable pid.0.index-enable ?

thanks as always Andy

Yes the code does the same thing
The index stuff is important if you want accurate homing
limit switch positions wander about