Re: [CAD_CAM_EDM_DRO] Re: Re: Re: Out of Estop.. BUT

Ray Henry wrote:

>
> Bertho
>
> We seem to be moving this topic toward one big BUT.
>
> It's a bit of a simplification, but Jon's servo amp uses at least
> three
> analog signals, motion command, tach feedback and motor current, to
> close
> the motor loop. Yes the position loop is digital. Sure the motion
> command
> is derived from a digital signal, and the product of the analog
> signals is
> PWM that triggers IGBT's.

So far, we are using power FETs, although IGBTs could pretty much just
be plugged
in, if the PWM frequency was lowered to 25 KHz or so.

> Yes all of those signals could be and are being converted to digital
> devices on some machines. That's why the latest versions of the top
> end
> machine tools, that I get to service, use pulse coders that run 125k
> ppr.
> One service guy said he's seen them produce as many as 0.5M ppr. They
>
> apply these expensive devices in an attempt to get smooth enough
> movement
> near the axis crossover points on a big circle so that a part doesn't
> look
> like it was made with a large bastard file.
>
> You're right about the screwdrivers and pots. But the production guys
> I
> know would rather put parts with arcs like that into an old machine,
> have
> me do a little adjustment to the analog circuits, and cut a part that
> is
> cleaner than the new, all digital, machine can make.
>
> Analog has it all over digital for both speed and resolution. I
> remember
> as a kid talking to a navy pilot. He explained how he wore contact
> lenses
> with mirrors ground into the edge. The analog signals from light
> bounced
> off those lenses were used to align his weapons to where he was
> looking. I
> can't even imagine the resolution required to hit a 10' target on a
> five
> mile radius. Or the speed required to do it to a 600 mph target from
> a
> platform that's going the same speed.

These "shoot where I'm looking" systems use the pilot's eyes or head to
aim a target
tracking RADAR or LIDAR to make a final lock on the target. But, the
pilot's eyes
can steer the radar to lock on a lot faster than he can do it with a
joystick or the
nose of the aircraft. Also, these systems almost always use "terminal
guidance",
meaning either the mother aircraft of the missile itself tracks the
target, and continually
refines the aim as it approaches the target. At 5 miles, even the radar
can't pick out
an individual tank in a tight group. When the missile is a couple
thousand yards out,
it can then zero in on one.

> A few weeks ago a biologist friend told me about someone who is making
>
> robot pets using simple analog circuts. She said the snake was very
> lifelike and would curl across your shoulder and around your neck. (it
> was
> set up not to be a constrictor)

Whew! I HOPE not! We have had a number of deaths in the area from
'pet'
constrictors.

> Try that with embedded linux and EMC, or
> Ahha or anyones digital. But for the home shop maybe digital is good
> enough!

I do a lot of circular borings, and I want them to be good! But, when I
need something to
be a truly fine circle, then I use a boring head.

Jon