encoder

[heilcnc]

will a 500CPR encoder work for spindle rpm or do i need less cpr for my lathe im building for threading was using 1 cpr with turbocnc but found good price on these thanks

[Seb]

Disclaimer: I'm no expert.

I think 500 cpr should be fine for speed control. The only concern is that you read the encoder fast enough to keep up with all those transitions.

Let L be the number of lines on the encoder.

Let R be the speed of the motor in revolutions per minute.

(4 * L) is the number of quadrature transitions per revolution.

(R / 60) is the number of revolutions per second.

(4*L) * (R/60) is the number of quadrature transitions per second.

F = 2 * (4*L) * (R/60) is the minimum sampling frequency (according to Nyquist, as I understand it).

That simplifies to F = (0.1333 * R * L).

So if you have a 500 line encoder spinning at 4K rpm, you need to sample the encoder lines at 266 KHz.

[samco]

plus - for emc2 to do threading - you need a index pulse. your encoder needs a and b channels + z (index)

[Seb]

Why does EMC need an index pulse to align the spindle? It seems like it (EMC) should be able to synthesize the index pulse from the normal A/B counter. It would have to know the cpr of the encoder, but that could be supplied via a parameter.

[samco]

emc is not setup that way.. Mainly it would work fine for making threads all the same durring one session. but if your making threads that have to be the same degree start lead or maybe you started threads and needed to finish during another session (machine gets turned off and on) you will not be able to make the same threads again without a bit of work.

sam