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PICList Thread
'[OT:] rotary encoders'
2004\09\04@095550 by hilip Stortz
2004\09\05@200616 by Cnc002

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In a message dated 9/4/2004 9:58:13 AM Eastern Daylight Time,  
spam_OUTmadscientist.at.largeTakeThisOuTspamearthlink.net writes:

does any  one know who if any one makes rotary encoders that produce 1000
pulses/rev  or 4000 pulses/rev in quadrature?  are there any that don't
require an  organ donation to afford?  this relates to the cnc stuff and
a  discussion on the emc (gpl cam software) list, particularly with
regard to  threading on a lathe (by controlling the 2 axis rather than
using  gears).

also, are there relatively large 3 phase servo motors still  being
made/used?  some people on that list talk about servo motors but  those
i've seen are just good dc motors with a rotary shaft encoder  servoed
with digital hardware.  if polyphase servo motors are still  being
made/used what level of resolution can you reasonably get from them?  
i'm thinking motors from 0.1 HP to a couple of HP.  i have seen  data
sheets for servo to digital resolvers, but at the time thought they  were
meant for updating older servo systems or for some kind of servo  rotary
encoder and always thought that most of the polyphase servo systems  were
in low torque environments.

it won't happen any time soon, but  after building my small mill i'd like
to eventually build a larger cnc mill  and lathe (not huge, smaller than
most Bridgeport's certainly).  by  planning ahead i can make some design
trade offs and know what to watch for  on the surplus/ebay market and try
and grab those rare deals.

this  is one of those areas that's hard to search with google, since you
find a  lot of complete systems and often few parts or theory, and less
indication  of what the best way to make something new is (every one says
their  approach is best, but it can't be best for all uses).  i've  seen
commercially available motor control stuff, and it's far too  expensive
for a hobbyist, particularly one who can design and want to  design their
own toys for added fun.  and most of the commercial  motion control stuff
isn't aimed at lathes/mills.

i also want to  start designing a good motion controller for these
applications that takes  "G" and "M" code and similar commands rather
than burden a host machine  trying to run an rtos with that part of the
problem (which seems for  efficient to me, and allows for multiple
interfaces).

I'm not sure the  approach used in the "emc" program is the best now.
there are newer  algorithms, and it's seen a lot of patching over the
years, apparently  without much documentation.  there are also motion
control  microcontrollers on the market, though it seems to me a dsp chip
might also  be a good way to go (and i've wanted to get into dsp, though
this isn't a  classical application it could help me get started).  i've
found some  good papers detailing better motion control algorithms and i
understand  them enough to implement it.  i think trying to integrate low
level  control with a GUI and an rtos just makes things harder to
implement,  though perhaps easier to debug.  the emc is fairly old, and
it  probably was a great idea at the time, but i'd like to try  something
different and i think compartmentalize the functions more and  move a lot
of it off the pc.  i do think that tool path generation is  best done on
the pc, since that needs to be somewhat interactive and needs  to be
"virtually" tested and edited.

also, for those building a mil,  the steppers i was referring to being
good and cheap multiple places as  surplus are "powermax II" steppers,
200 steps/revolution (full steps!) and  have a 0.1" lead spacing
connector that works good with the amp mta  connectors.  the specific
model number i've seen (for those googling)  is "P21NSXC-LSS-N8-03" and
the data sheets are at fluidmetering inc.'s web  site i believe (i
haven't looked them up for months, but a friend has them  on his sherline
and i had looked them up as i'm helping with his driver  electronics).
also, allegro makes a nice 2.5 amp stepper motor driver chip  in a plcc
package that works nice with these and is on some of the driver  boards
being sold.  most places are selling these motors for $5 ea.,  and i had
seen some on ebay as well.  for my mill i'll be using double  shafted
steppers from jameco most likely (i want manual control for simple  things).

it'll probably be a 6 months or more before i build my  hardware and
start playing with microcontrollers to run it, but i do like  to let data
simmer for a while anyway.  i'd love to make a controller  good enough to
sell to other hobbyist.


There are a lot of encoder manufacturers that do make quadrature rotary  
incremental encoders with 1000 and more pulses per revolution.  Alas, they  are
NOT cheap.  They can range from around $200.00 USD to over $1,000.00  USD
depending upon the application in which they are needed.  Some  manufacturers are
U.S. Digital, Eltra (Italy), Hoehner (Germany, Canada), Litton  (German), BEI
(US) and many others.

Yes, there are three phase AC servo systems out there.  In fact, that  is
what many, if not most, of your industrial mills and routers are now  using.  
Yaskawa comes to mind first and I think Allen Bradley has a line of  them as well
as does Fanuc.

Unfortunately, none of these are cheap.




Randy  Abernathy
4626 Old Stilesboro Road NW
Acworth, GA 30101-4066
Phone /  Fax: 770-974-5295
Mobile: 678-772-4113
E-mail:  .....cnc002KILLspamspam@spam@aol.com

I furnish technical support, repair, and other  related services for your
industrial woodworking machinery. My background as  Senior Service Engineer for
the SCMI Group for nearly fifteen years with factory  training, combines with
my extensive background in electronics, mechanics,  pneumatics, electrical and
CNC machinery to offer you needed support for your  machinery.
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2004\09\05@203935 by hilip Stortz

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thanks!  are those 3 phase AC servo systems using a 3 phase motor and
electronic servoing, or are they classical 3 phase servo motors that
were originally (long ago) driven by a 3 phase rotary encoder?  there is
a difference, and while i won't be using either any time soon (i'll be
using split phase power at best, if i get a large mill/lathe with a 3
phase spindle motor i'll most likely replace it with a single phase,
even though the torque won't be as smooth, otherwise i'd build a 3 phase
power source, especially since that's getting easier).  true 3 phase
servo motors can be held in any position with 3 steady voltages, or
rotated at a variety of speeds with a variable frequency 3 phase source.
i would think that any ac motor of several horse power capable of a
wide frequency power range would be both difficult and expensive to make
(since the winding inductance is normally very important in an ac motor).

i'll doubtless only be doing small stuff for some time, and probably
mostly using stepper motors since they are cheap and easy even though
not power efficient, and a speed controlled dc motor for the spindle (i
have motors from old, 1" real to real instrumentation recorders, should
be great.  i also have the heads and wish i could sell those along with
many other parts, including the huge, rack mount power supply which
should be very handy!).  none the less, i probably will eventually by a
used mill/lathe and want to convert it, and i'll definitely want to be
able to do threading and similar jobs on the lathe.

Cnc002spamKILLspamaol.com wrote:
-------
> Yes, there are three phase AC servo systems out there.  In fact, that  is
> what many, if not most, of your industrial mills and routers are now  using.
> Yaskawa comes to mind first and I think Allen Bradley has a line of  them as well
> as does Fanuc.
--------

-- Philip Stortz--"In Germany they came first for the Communists, and I
didn't speak up because I wasn't a Communist. Then they came for the Jews, and I didn't speak up because I wasn't a
Jew. Then they came for the trade unionists, and I didn't speak up because I
wasn't a trade unionist. Then they came for the Catholics, and I didn't speak up because I was a
Protestant. Then they came for me, and by that time no one was left to speak up."
-- Martin Niemöller, 1892-1984 (German Lutheran Pastor), on the Nazi
Holocaust, Congressional Record 14th October 1968 p31636.

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2004\09\06@042028 by Roland

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At 06:40 PM 05/09/04 -0600, you wrote:
>thanks!  are those 3 phase AC servo systems using a 3 phase motor and
>electronic servoing, or are they classical 3 phase servo motors that
>were originally (long ago) driven by a 3 phase rotary encoder?  there is
>a difference, and while i won't be using either any time soon (i'll be
>using split phase power at best,

Hi
Most of the new machines use 3-phase servo motors with linear feedback on
the bed. In fact the latest trend is for all linear axis to have linear
motors. It seems that the rapid traverse speed on machines is the slowest
part of the operation.
It boggles the mind to imagine about about 50Kg of steel moving around at
7g's and working to .001mm

Regards
Roland Jollivet

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