On 2010-06-10, Ignoramus967 wrote:
I inspected the motor more closely. There is another set of larger
brushes that clearly are for actually running the motor. These tiny
brushes are likely to be a tachometer.

Great! And you have a servo amp which accepts the tachometer
wires.

Note that the easiest thing to get wrong is to wire the tach (or
the motor) wires backwards. If that is done, it will shoot to full
speed on one direction or the other no matter what the command voltage
is.

Just test this with no mechanical connection to the machine to
make sure it is right before you let the amp and motor run the machine.

If you have a lab type power supply which can put out any
voltage between 0V and 10V, you can run at any speed within the motor's
range. If the amp is not the one which came with the motor and machine,
you may need to adjust the feedback gain so your 10V is truly the
maximum RPM you want. The motor's label should tell you both the
maximum speed *it* can take happily, and the volts/1000 RPM from the
tach, so you can use a DC meter on the tach leads at the amp to see what
speed you are really getting.

Anyway -- the lab supply will give you all possible speeds in
*one* direction, and you will have to swap ground and + to the servo amp
inputs to get it to run in the other direction.

Or -- you could set up a pot between +10V and -10V with either a
pair of resistors defining a 0 voltage reference and use the pot to get
all speeds within the range of the motors.

Of course, again while playing with this, you want the toothed
belts off the motors so you don't drive anything hard against a stop.

Set up the travel limit switches to shut down the amp if it hits
one of them, and make sure that always works before you let the motors
actually move the machine. (This applies, of course, whether you have
tach feedback or not. :-)

I would suggest using relays on the limit switches, so each one
will stop the servo motor moving in that direction, but allow moving in
the other direction, but other contacts will also hit the E-stop on the
controller as well, since if you hit a limit switch you want to stop all
other motion as well. For convenience, given how buried some of the
belts are, you might want to provide a pair of low voltages (perhaps +/-
0.5V or so) to feed to the servo amps to back off a limit switch while
the computer is shut down. The Anilam conversion which I used at work
had handwheels, but your (and my) Bridgeports do not. If you can find
them, set up military style pull-to-unlock toggle switches (the kind
which arm weapons on aircraft) for connecting the slow motion voltages
into the servo amps. This way, someone has to *think* before they
interrupt the control signals to the servo amps.

Enjoy,
DoN.

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