Re: [CAD_CAM_EDM_DRO] Aligning servo motor encoders

Jason Cox wrote:

> Hello,
>
> Could somebody please explain the method and impotance of aligning an
> optical encoder to a servo motor?

Maybe. It depends on how the encoder is attached. There are encoders that
become part of the motor, such as the ones with bare discs and a sensor
module that you mount on the back of the motor. There, the alignment
is to get the photo-sensors right over the optical track of the disc.

If the encoder is a separate shafted component, then you want to have the
encoder as coaxial to the motor as possible. This is both for the angular
as well as radial displacement alignments. Either will cause force to be
applied to the encoder shaft, as well as flexing the shaft coupling which
will eventually fatigue the coupling. For encoders, a solid coupling made
from a single piece of aluminum is generally the best choice. Servometer
couplings made from a bellows-like material is also very good, but these are
even more expensive than the helical-slit couplings.

Establishing the correct alignment depends on the tools you have available,
as well as the suitable reference locations on the parts that you can use
for such measurments. If the encoder will be mounted to the motor, you
might want to use a dial test indicator to center the motor on a lathe or
mill, and then install an adaptor housing to be concentric. If both the motor
and encoder have a raised boss or register that is concentric to the bearings,
a tube with IDs bored at each end to just clear these registers will force the
encoder to be concentric to the motor. It depends on how good you are with a
lathe.

If the motor and encoder will be separately mounted to a base plate of some
sort, then there are a bunch of tolerances that have to be considered. there
will be mounting brackets for motor and encoder, and mating holes in the
base plate that hold these parts aligned.

Without more details of the setup, I can't be more specific.

Jon