Re: gearmotors,encoders

Jack,

Good morning! I see no problem mounting the encoder at the farr end.
It's hard to imagine a leadscrew torsionally twisting even 1 encoder
count.

You might want to try Servo Systems Co. (1-800-922-1103, Ext 19) for
motors and encoders. Talk to Jim Werba there, he is a very
knowledgable applications guy. Have them send you a catalog.

As to how to mount the encoder, others will know better. I'm just a
dumb EE.

Mariss

--- In CAD_CAM_EDM_DRO@egroups.com, jmw@c... wrote:
> Thanks, Mariss. I understand what you're saying about no-windup
> connections between the motor and screw, and I suppose that also
> includes gearmotors.
>
> What do you think about part 2), putting the encoder on the non-
motor
> end of the screw? Is there likely to be a problem due to, ah what
> would an ME call it--the torsional flexure of the lead screw? I'm
> guessing it's going to be a lot easier to find surplus servos with
> tachs than with 1000 line encoders.
>
> Incidently at least one encoder mfr (Dynapar) suggests the
fiendishly
> expensive helical connectors for connecting encoders.
>
> --Jack
>
>
>
>
>
> --- In CAD_CAM_EDM_DRO@egroups.com, "Mariss Freimanis"
> <geckohall@h...> wrote:
> > Hi,
> >
> > The problem is backlash. The servomotor will thrash back and
forth
> > over a distance equal to the backlash, building up a good head of
> > steam on each transit. Expect considerable vibration as it does
so.
> >
> > The motor gets its guidance from the encoder. In the backlash
> region,
> > the motor can move, (and it will) without any compensating motion
> of
> > the encoder. The motor then is uncontrolled and will accelerate.
If
> > the backlash is large, the motor speed will be cosiderable when
the
> > encoder finally moves. It will then reverse direction and the
> process
> > will repeat.
> >
> > Mariss
> >
> > --- In CAD_CAM_EDM_DRO@egroups.com, jmw@c... wrote:
> > >
> > > ----------------------------------------------------------------
--
> --
> > -
> > >
> > > Apologies in advance for burning bandwidth; I've asked about
this
> > > before--but I still don't get it. Why not put rotary encoder(s)
> on
> > > the non-motor end of the screw rather than on the motor shaft?
It
> > > seems like one wants to know the position, direction and speed
of
> > the
> > > screw rather than of the motor per se. So if it's no worse,
> > possibly
> > > even better, to have the encoder on the far end--then what
would
> be
> > > wrong with a slightly flexible coupling (e.g. Lovejoy) between
> the
> > > motor and the screw? I can see that during accel and decel the
> > motor
> > > and screw could get out of phase, and maybe in some bitter
state
> of
> > > the world this could feed on itself, but couldn't this problem
be
> > > tweaked away with a little gain correction? I like slightly
> > flexible
> > > connections; they absorb vibration, correct for slight
> > misalignment,
> > > would put some allowance for a few thou of axial heat-growth of
> the
> > > screw in the system, etc.
> > >
> > > Thanks.
> > >
> > > --Jack