On 2013-02-01, wrote:
On 1 Feb 2013 05:27:47 GMT, "DoN. Nichols"
wrote:

On 2013-01-31, wrote:
I am working on a 5th axis for the mill. I think it will need a brake.
I'm not sure if the servo motor will be able to hold position for some

[ ... ]

DC servos? What amount of motion can you tolerate. I would
expect with steady/slowly-changing loads no more than one or two encoder

[ ... ]

Now -- if there are serious pulse loads, then you might have a
little more error before the servo loop could fix it.

[ ... ]

Grewetings DoN,

There will be pulsed loads. Such as when an end mill is spotfacing
and/or counterboring a curved surface. I don't know yet if I will be
contour milling with the 5th axis. Probably not at first. I just need
to be able index the parts. To do this I will be using an M code to
send a signal to an Arduino. The Arduino will then command the 5th
axis to move. I'm still learning how to use the Arduino and the LCD
touchscreen display I bought for the Arduino. I still need to figure
out how to get the signals from the encoder to the servo amp.

The part of the encoder which requires connections should not be
moving relative to the motor -- so cables to the motor and cables to the
encoder could be strapped together -- but shield the encoder cables to
avoid noise from the motor from introducing errors.

The encoder (on a motor, at least) is typically a slotted disc
(or a glass/quartz disc with slots printed on it by evaporation of
metal). This is mounted to the back end of the motor shaft. Bolted to
the back of the motor housing is a set of LEDs and photodetectors (along
with matching slots in a stationary part). Wires go from these to the
Arduino or whatever you use.

I don't
know yet if slip rings will do or if I need to get some type of
wireless setup.

Just plain cables for the encoder connections.

Now -- if you want the brake which started this, you typically
have a brake disc on the shaft, with a spring mounting (not much give)
and an electromagnet mounted tot he motor to attract the disc to contact
a friction surface.

But I need to approach this project with what I do
best first, and that's mechanical stuff. I think I have the drive
figured out, now I need the brake.

Adding both encoders and a brake to the back end of the motor
will be a bit tricky. An alternate encoder is one to directly measure
the motion of whatever -- I'm assuming a rotary table or something
similar -- and measuring at the table instead of the motor means that
you don't have as much resolution for the same encoder. For linear
motion, there are linear encoders which mount to the moving part, with a
reading head bolted to the stationary part -- well sort of stationary,
such as the head bolted to the saddle of a mill, and the encoder bar
(which has no wires) bolted to the edge of the table so the table pulls
the bar past the reading head.

Good Luck,
DoN.

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