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Unread 01-05-2009, 14:10
Frank Neuperger Frank Neuperger is offline
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Frank Neuperger is a splendid one to beholdFrank Neuperger is a splendid one to beholdFrank Neuperger is a splendid one to beholdFrank Neuperger is a splendid one to beholdFrank Neuperger is a splendid one to beholdFrank Neuperger is a splendid one to behold
Re: Sensorless back_emf speed controller

Interesting discussion. I will have a look at the waveform on the output of the Jag and see if the back emf is observable between jag pulses.

We used encoders for the back emf estimation this year with great success in implementing out traction control and anti-skid braking.

The most difficult issues were the centering of the KOP (read bearingless) US Digital encoders. US Digital FAE recommended staying below 0.010" bearing radial runout and maintaining the spacing between encoder wheel and the optics by the same tolerance.

The radial runout is not hard to comply with if you are on a shaft supported by 2 bearings and have a decent mount for the encoder. Sadly the $2 mount was not not supplied in KOP and likely lead to the destruction of many KOP encoders because of incorrect mounting.

We found the axial spec was much harder to deal with on the Banebot P60 gearboxes due to the huge slop on the factory shaft wandering in and out of the transmission +- 0.050. After we made our own 3/8" output shafts, the tolerance was much MUCH better but still not within the 0.010" recommendation. I am estimating +- 0.020 worst case. The system did however work OK. If you are too far form the encoder, you lose counts, but if you get too close there reader optics can scratch the encoder. If it rubs long enough , you will scratch the reader lenses. The lenses are recessed and thus protected by a raised plastic lip around the opto chip that needs to wear off before the lenses can be scratched. By the time it wears down, the encoder may be scratched badly. We did have some scratching on one encoder (not the lens) because of some misalignment but it continued to function OK.



Regards
Frank Neuperger
TEam 39
 


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