Re: one axis closed loop control

I'm facing the same challenge with an emco lathe that I'm retrofitting
with "generic" stuff. Rather than indexing, I'm putting a
step/direction control on the spindle. May be a big stepper with
a Dan Mauch 5-amp driver, or a servo with a Gecko320. Drive it
as an axis under cnc (CNCPro from Yeager in my case) when doing
threading, fusee-making, fluting, or by a 555-based pulse generator
when running at constant speed.

That's *my* way around changing software...
There are some nifty looking rotary encoders on ebay, for 7 bucks
(800 line, use a toothed belt) /mark

--- 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. Books by Colvin, Law, Barber-Coleman, and a very
> interesting article in MEW magazine explain the gear hobbing
process.
> Its one very versatile method of making almost any gear form.
>
> In very short summary, you can hob on a mill by mounting a hob
cutter
> (I've been buying 'em up on Ebay) in the quill and rotating the head
> by the helix angle. You then need a driven 4rth axis to mount the
gear
> blank in. This could be a rotary table mounted vertically, an
indexing
> head or something similar.
>
> Then the hard part: Driving the 4rth axis. For many many years this
> was done with gearing. The Ivan Law book shows a complex method to
do
> this with lathe change gears. Today, driving the 4rth axis is done
> with a stepper motor in closed loop with an encoder on the spindle.
> Basically, the 4rth axis must rotate exactly one tooth for every one
> turn of the spindle. The MEW article ('Model Engineer's Workshop'
> issue 75, July/August 2001) shows a method of building an encoder
and
> stepper to drive the 4rth axis. This author must be a total
> electronic type. He spent three pages describing how to build a 4rth
> axis (the really easy part to understand, for me) and one paragraph
> and an electronic drawing showing how to closed loop drive a
stepper.
> For me, I still have NO IDEA how to construct this.
>
> Right now, I'm building a 4rth axis with a D1-3 spindle nose and
worm
> gear drive to a stepper motor. This can be used on my CNC mill for
> many projects. My CNC control (Ahha Artisan) can drive a 4rth axis,
> but its open loop only, as nearly all PC based controls are.
>
> I've been watching for a method to closed loop drive this 4rth axis.
> So far, I've only got possibilities:
>
> 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