Re: Hand held pendant

> From: "Dan Mauch" <dmauch@...>
>
> I bought one of those quadrature encoder to step and direction adapters from
> www.usdgital.com I got the P-84-4 which is the size of a finger nail. It
> plugs into an HEDS type encoder and provides step and direction output. They
> sell for $16. I put one on a motor that had a 200 CPR encoder and connected
> the step and direction output to a stepper motor driver. It worked slick. I
> simply turned the encoder one direction or the other and the stepper motor
> followed .
> I turned it at various speeds and it followed. Just like a real low cost
> servo system with HIC ( Human Interface Control) :)
>
> I also tried a 2000 CPR however it was too fast for the the stepper. So I
> could see using one of those $14 encoders from Brigard's for another kind of
> manual control of a cnc system. It looks like a 400DPI mouse may even work.
> My self, I have had several controllers that I designed that used a manaul
> pendant. Other than for flycutting they're not that handy.
>

I don't know about you, but I do more "that looks about right"
machining than precision stuff. If I say need to turn a hole into a
slot on a mounting bracket - I just want to turn wheels and translate
an endmill around, not write a program or mess with the computer at
all. However I get the sense that if I use steppers, I can simply
crank the handwheels with the power off, the drag of the coging
steppers through the timing belts replacing the old leadscrew drag
that would be eliminated by the ballscrews.

Suprised at what you got charged for the encoder - step/direction
converter. Was it all packaged and pretty? We used the LS7084 chips
(8 pins, needs maybe a capacitor in support) with very high resolution
(100 micron) glass scales on an air-bearing slide moving at around
1.5 m/s (the MIT 3d printer) and they worked wonderfully. Best part
was the price - when we ran out I called LSI Computer Systems, and
while they wouldn't sell us any direct they sent me a few free
samples.

Silly qestion: why go to step and direction when a servo motor is
essentially a quadrature device? (Answer: better control of stepping
- ability to half step, etc).

One thing that I think might be intersting to do with a manual pendant
on a CNC machine is to let you control motion along a fictional axis.
Sort of like a super-versatile compound slide, or software rotary
table. Turning the handwheel could cause it to advance along some
nonlinear taper, or a circular (eliptical, etc) path.

--
Christopher C. Stratton, stratton@...
Engineer, Instrument Maker & Horn Player
(978)538-5179 work, (617)492-3358 home
30 Griswold Street Cambridge, MA 02138
http://www.mdc.net/~stratton