Jon,
I just noticed the data sheet for the AD650 contains a link to an
application note specific to F/V conversion. The link is broken, but I
did find it after some searching. It seems like the hard part will be
at or near zero speed.
Here's a link to it anyway...
http://www.analog.com/static/imported-files/application_notes/75729603AN-279.pdf#xml=http://search.analog.com/search/pdfPainter.aspx?url=http://www.analog.com/static/imported-files/application_notes/75729603AN-279.pdf&fterm=application&fterm=notes&fterm=279&fterm=application%20notes%20279&la=en
Regards,
Steve
Steve White wrote:
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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