On 02/12/2020 12:43 AM, andrew beck wrote:
Hi guys
wondering if anyone has any ideas here.
I have a heidanhain spindle motor that runs up to 10000 rpm and has a 5v
sin cos encoder on it. I am currently controlling the motor with a
schiender vfd. I am talking to the support engineers here in New Zealand
about buying a encoder card so I can get better low down torque. If I run
the card in full encoder closed loop control in the vfd I can get 200
percent of the torque right down to 0 rpm for 30 seconds or so which is
pretty useful. I am currently just running the drive in Variable frequency
control which rapidly looses torque at low rpm.
Anyway they have a bunch of cards I can use but don't have a encoder card
that is suitable for sin cos encoders. I have no trouble changing the
encoder but am not sure if I can get a source of encoders that spin up to
10k rpm.
Is this a current-output encoder or a voltage-output one?
Heidenhain makes both. For current-output,
average current is 11 uA or so. So, you can run that
current into a 1K resistor and get 11 mV.
Feed it into a comparator with the other input set to 5.5 mV
and you should get a nice square wave.
Adjust the threshold voltage to get a 50% square wave and
you are done. You probably need
3 of these circuits to handle A, B and Z, if provided. If
not, then you need something a little more
tricky if you want a spindle index signal.
If this is too noisy, change the 1K resistor to 10 K, then
you will get 110 mV output, and up your threshold to 55 mV.
If the encoder is voltage-output, then you just get rid of
the resistor.
How many "pulses" does the encoder have? Just one? I hope
not, that would make this scheme not
work well. Then, interpolation would be required. But, I
can't imagine how to make a reliable optical encoder
with just one pulse/rev.
Jon
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