Re: [CAD_CAM_EDM_DRO] Re: Digest Number 2382

f32cpe wrote:

> I am also considering using an older mill (mid 1970's?) autonumerics
> positool cnc ? I assume I would have The same problem with the servo
> amps being that old (I was told that the older controllers could be
> temperamental but they weren't specific). I am new at trying to do
> this, so I was wondering the best way to start and what I will want
> to keep and what I won't need (losing alot of garage space) I would
> like to use the old servo motors if practical because I have a few
> extras. How would I check if it has a encoder or resolver? Also
> would I still be able to use the old power supply for the servos if I
> got or made new servo amps. I am planning on making it pc
> controled. Any help to get me started would be appreciated.

I think the older servo amps are probably more reliable than the
older CNC control computers, but it depends on the safety factors
taken in the design, so it may not be true of all models.

The first thing is to find out whether you have shaft encoders or
resolvers for position feedback. Encoders are easily connected
directly to modern CNC interfaces, resolvers need something in
between to excite and interpolate the signals.

First, look for labels on the motors, and anything near the motors.
That may be all you need. If not, you may have to trace wires,
or take them apart. Encoders will generally have LEDs or light bulbs
shining on a glass or metal disc with a slot pattern in it. (Linear
encoders have a long glass bar with the same sort of grating pattern.)
Photodetectors on the other side of the grating pick up the light.
Resolvers have coils of wire, and may look a lot like an AC motor
stator with a wound rotor inside. Resolvers will almost certainly have
6 wires, encoders can have just about any number. Encoders will
have DC power supplied to them, resolvers would have low-level
AC excitation, usually at a high frequency like 400 or 800 Hz.

The servo power supply will almost certainly be reusable. the only
problems would be if it takes 3-phase, or if these are the hideous
old SCR servo amps, which had no DC supply.

Jon