Re: one axis closed loop control

Hello Karl,

1)You might want to talk to the inventor of the Frog (I think his
name is John). Unless he has hard coded some time constants for the
small motor he uses, you should be able to amplify the signals and
drive a larger motor. If you can get him to help, it will of course
be easier. I suspect he might be open to the discussion.

2)"slaving" a stepper to an encoder is a "staple" of the
manufacturing industry. And it's pretty easy to write a program to do
it. (or find one already written and in the public, or at least
sahreware domain) You would mount the encoder on your spindle and
issue a step pulse every so many counts...

In fact, Microkinetics has a motion library called instep which
includes this function; they use it for threading (and multi-start
threads) on their cnc lathe program. But the library is available
royalty free for about 100 bucks. Down side is, it "wants" THEIR
interface/motion card (still don't get sumthin' fer nuthin'). But
might be worth a look.

3) you wouldn't necessarily need a "commercial" encoder. You could
mount magnets on the spindle pulley and just "count" them with a very
simple circuit. This would likely involve the use of a pic
microcontroller, which could then perform the "slaving" function and
dispense the pulse train for your stepper (or step-servo). Thisis
open loop, but could be "improved"(not sure that you need it tho) to
closed loop.

2a) there are SCADS of commercial single axis closed loop setups.
MANY more than cnc types, since these don't need multi-axis inter-
related realtime control. Be sure to look around a little more...
"process control" may be a useful buzz word or search term.

Hope this helps.

Ballendo

--- In CAD_CAM_EDM_DRO@y..., "karl_l_townsend" <karl@c...> wrote:
>I've done a lot of study toward making a gear hobbing machine out of
>my CNC mill. <snip>
>1. There is a closed loop control used on micro lathes for
>threading. It's called "The Frog" and is advertised in HSM magazine.
>But you have to use his extremely small stepper - not enough beef
>
> 2. It looks like Parker Compumotor Inc. sells a stepper control to
> drive a stepper based on an input shaft encoder. Looks very spendy.
> Haven't got a price quote yet.
>
> 3. Get someone in this NG to tell me how.
>
> Karl