Jon,
I'm the guy from the CNC Workshop that had the Yaskawa encoder
documentation you needed for testing the resolver to quadrature
conversion. I also had the Panasonic servo motors / drives and a lot of
other junk for sale there.
Have you looked at the AD650 (also from Analog Devices)? I've never
used any, but the data sheet looks like it might have potential. Here's
a (really long) link to the data sheet. The AD650 is easy to find on
their web site too if this long link fails.
http://www.analog.com/static/imported-files/data_sheets/AD650.pdf#xml=http://search.analog.com/search/pdfPainter.aspx?url=http://www.analog.com/static/imported-files/data_sheets/AD650.pdf&fterm=f/v&fterm=f/v&la=en
Regards,
Steve
Jon Elson wrote:
>I mentioned to some people at the CNC Workshop that I was
>working on a resolver to quadrature converter board, and we
>hooked one up to a servo motor to compare a real encoder against
>the AB signals derived from the resolver. That all worked quite
>well.
>
>Well, a customer also wanted a velocity signal from it to
>simulate a DC tachometer. I said "Oh, simple, it has a digital
>velocity output, I'll just hook that to a DAC and it is done!"
>Ahh, not so fast. The AD2S1200 chip is designed to run up to
>1000 RPS = 60,000 RPM, so if full scale of 2047 (12-bit signed
>binary value) is 60,000 RPM, then one bit = 29 RPM. Oh oh, that
>is never going to work to close the loop of a positioning servo
>like on a machine tool axis! I've confirmed by twirling the
>resolver shaft that this appears to be the true scale factor for
>the chip.
>
>So, I am going to have to develop the velocity value from the
>quadrature signals. Since the chip interpolates the resolver to
>4096 counts/rev, I should be able to produce much better
>resolution at reasonable speeds. For instance, at 60 RPM, you
>get 4096 counts/second. At 100 counts/second, it would be
>turning only ~1.5 RPM, so some really simple filtering should
>work. I'm trying to decide if I should do this digitally or
>have encoder counts produce fixed-width pulses on a pair of
>charge pumps, one on each input to a differential amp.
>Digital would get rid of all the adjustment pots, of course.
>
>Any thoughts?
>
>Jon
>
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