On Fri, 29 Apr 2011, Jon Elson wrote:
> Date: Fri, 29 Apr 2011 00:33:49 -0500
> From: Jon Elson <el...@pico-systems.com>
> Reply-To: EMC developers <emc-developers@lists.sourceforge.net>
> To: EMC developers <emc-developers@lists.sourceforge.net>
> Subject: Re: [Emc-developers] Fanuc converter
>
> Chris Radek wrote:
>> If you really have 65K-1M per rev, though, dP/dt is going to give you
>> a better than usual velocity estimate. If your hardware can measure
>> the real dt instead of the driver trusting the pc latency to be
>> negligible, even better?
>>
>>
> Well, this is somewhat confusing. Apparently, these Fanuc encoders have
> an interpolator that increases the resolution of a basic 2048-line
> encoder wheel. At low speeds, the absolute position report is good to
> either 65K or 1 million counts/rev. At some speed, it apparently zeroes
> out the interpolated part and only reports the 4096 count/rev part
> direct from the encoder. Probably at those speeds, there is no problem
> with that, but it seems there might be some kind of discontinuity as the
> interpolation is switched on and off.
Certainly at high speed the interpolation is not of much use, but the
interpolator will of course also go bad at 0 speed.
We've considered using such and interpolator with our embedded motion
controller to avoid the (expensive if embedded) divide used for velocity
estimation. The interpolator is just a second order DPLL, fairly easy to build
into the encoder logic, and has the advantage that the velocity falls out
directly from the first accumulator.
>
> Well, as none of this seems to be available in external documents, I
> will just have to experiment with it. I have a guy sending me a motor
> to work with.
>
> Jon
Peter Wallace
Mesa Electronics
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