Re: gearmotors,encoders

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