RE: intro and a few questions

["Pete Cook" <pete.cook-at-alltracorp.com>]

This would probably take a little modification - most torch (be it oxy or
plasma) applications want some feedback from the torch (arc transfer for
plasma or Cut oxy on) to know when to move. You also may need some pierce
delay to get through the material be fore moving. I would suggest using some
M-codes (like coolant on off) to turn the torch on and off. For Oxy/fuel you
migh also need a preheat delay as well as a pierce delay.

> 1. is the torch on-off really another axis? can anyone
> suggest an means of
> control.  it would be a simple off/on solenoid type control.

I would say servos are the way to go if you have the financial resources to
finance them. With a high number of encoder counts you would have excellent
control over the motion with smoother torque and a broader speed range
compared to steppers. Steppers have a simpler interface - just step and
direction - which works fine as long as the motor is big enough so that it
will not miss steps( which means that steppers have to be oversized as
compared to servos&encoders) But there does come a point where bigger
stepper motors give no more performance because the motor inertia gets too
big (try putting a huge diesel in a dragster)
If you can afford to go with servos, it is the best choice, but steppers
will work within their limitations.
There is an Australian company that makes a servo amp that is controlled by
stepper inputs (probably uses a pair of counters - one driven by the step
and direction inputs, the other by an encoder - that go through a binary
comparator to an D2A converter to an amplifier and then to the servo motor)
that would drive higher performance servo motors with the cheaper stepper
interface.

> 2. the only other thing at this point that is holding me back
> is the motors.
> stepper or servo or chopper type. i tried a couple of the links to the
> stepper motor tutorials, but they seem to be dead.
> can someone point me to a resource or faq for them?
>
I don't have much input here as far as steppers go - some 80 - 100 watt
servos would probably be plenty - maybe even overkill.

> 3. lastly, the whole notion of torque ratings of the motors.
> again, pointers
> would be great. i don't think i need gorilla torque or
> speed..  i am looking
> for 10-80 inches per minute travel. i have been scouring the
> scrapyard for
> motors, and surprisingly enough, i see A LOT of them, but
> havn't been able
> to identify my needs.
>
It would seem that these questions are rather important for the future of
EMC - if you can't get help with the real world side of EMC it becomes just
a nice acedemic problem with little use beyond that.

> again, i know this is mostly a dedicated emc list, but i am
> hoping someone
> can point me in the right direction to get over these last
> remaining hurdles
> to get going.


Pete