RE: [CAD_CAM_EDM_DRO] PIC DRO stupid question

I have not followed this DRO discussion, however, I did print a pattern on
an HP Design Jet 230 Plotter just to see what it might look like. The
minimum line width of the Design Jet 230 Plotter is about 0.010", so I
tried placing a few 10 mil lines on a 20 mil spacing, as well as some 20 mil
lines on a 40 mil spacing and so on. I made some polylines in triangular
patterns. I found that the accuracy of adjacent lines was not perfect (and
this could be seen under a magnifying glass). I didn't investigate to
qualify the lack of perfection as to all of the possible issues including
the software I was using, if the small errors between lines did or did not
mean accuracy problems over great distances (I suspect not). I left the
issue as to my simple observation. The lines were a tad skew'd. Every other
line was a bit North in appearance.

My gray matter exercise for DRO concepts for has left me with the conclusion
that the "scale" is a key component. Such a statement will get a good round
of "Dahhh Dude" responses, but of alternative concepts to scales, I liked
the precision ball bearings stacked against each other in a tube. If
extremely high precision balls are stacked next to each other, it is a
pretty good ruler (scale). There is a DRO which uses this concept on the
market. The reason I bring this up, is that while making a home shop scale
of high precision might be a challenge for some, purchasing precision balls
is not so difficult.

The recreational discussions then go in the obvious direction about how to
read the balls and turn that into where in the hell are we. Probably if I
would read all of the past posts, some of that might be obvious (to me). For
the purpose of putting up a low cost accurate DRO, the other obvious point
is to purchase the scale (the difficult part), and kluge up the rest of it
(if within one's ability). I don't know what a glass scale and reader head
cost, but like others I'm not afraid of the electronic side of things. It
seems a rather simple electronic task to interface a scale into a computer.
A little software which many have already written and away you go.

It isn't all about what's been done before. It's fun to throw the balls in
the air and see what comes back. The DRO on the market which uses precision
balls for the scale, has a series of coils which I suppose are in a
multi-phase manner with fractional or specific spacing (probably different
than the diameter of the balls) for the coils resulting in a ripple
signature through the receiving coils which is, phase sensitivity and
proportional to position. If anyone wants details (which I am not aware of),
the patent has likely issued and full disclosure is a click or two away.

Some of my professional work is concerning optical interfaces and one of two
patents should issue next year, followed by another a year later. I can say
that optically reading the position of balls is in there. To obtain a
quadature signature, you can space the optics at a different distance than a
multiple of the ball diameter and you've got multi-phase signatures. Add the
right kind and enough optical sensors and the resolution potential is good.
Keynote issues with optical methods include the fact the optical emitters
and receives age and the intensity of light should be a closed loop system;
that differential methods are better than single ended, and so on. All
do-able stuff. If you bounce light off balls at obtuse angles, when light
hits the North pole it peaks in reflected intensity like a "fun-house"
mirror. Good stuff to obtain a strong signal from. Some stuff to work out
though. The magnetic models for sale have a strong advantage of "dirt free"
reliable operation. Dirty balls and optics are a problem. Fun stuff to
banter about.

David R. Howland




-----Original Message-----
From: Wayne Bengtsson [mailto:wbbengtsson@...]
Sent: Friday, April 07, 2000 2:22 AM
To: CAD_CAM_EDM_DRO@egroups.com
Subject: RE: [CAD_CAM_EDM_DRO] PIC DRO stupid question



-----Original Message-----
From: Jon Elson [mailto:jmelson@...]
Sent: Friday, 7 April 2000 1:58 AM
To: CAD_CAM_EDM_DRO@egroups.com
Subject: Re: [CAD_CAM_EDM_DRO] PIC DRO stupid question

>Really, if someone can come up with accurate grating patterns on film or
>glass, it is fairly
>easy to make your own linear encoder. Does anyone have any ideas on
>where to get
>such grating patterns?

One quick and easy way to make such a pattern would be to draw the pattern
in a good CAD program, and print the pattern on to transparency material
using the best quality injet printer you have access to.

I am assuming a resolution of 300 DPI would translate into .003" accuracy,
at a minimum. If anyone here has actually tested the output of a printer for
accuracy, I would be very interested to see the numbers.

Ok, that's the hard part done, how do you do the easy bits? :-)

Best regards
Wayne Bengtsson




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