Charles,
I've noticed the same small bit of coating removed from the reeds in my
optacon.
They are more or less the same spot per column, and slightly shifted per
row.
I suspect this was done during assembly to match the resonant frequency of
each reed + pin.
The added mass of the adhesive and the pins changes the resonant frequency.
The difference in mass from the longer pins would explain the shifted
position per row.
I would love to learn more about your design, but perhaps it is better if
we continue this off list?
Your email address is hidden from the list. You can contact me at
wannes.sels@xxxxxxxxx
Kind regards,
Wannes
On Mon, Sep 21, 2020 at 9:21 AM Noel Runyan <noel@xxxxxxxxxxxxxxxxxxxxxxx>
wrote:
Charles,
What do you mean by "coating". Do you mean the metal coating on the
top and bottom of each reed?
I have a box of about 10 thousand reeds, with 100 per bottle. We
checked and they, not surprisingly, all appear to have only the bare
silver on their top and bottom. They each have a red paint spot on
one surface, about the middle of the length. The red spot indicates
the polarization of the piezo reed, as the reeds were poled at the factory.
We also just examined a full Optacon array and the reeds are bare
metal, with no extra coating. Is it possible that any coating you
might have felt on the reeds was the solder that attached the circuit
contact end of the reed to the driver PCB?
I've only seen TSI's piezo reed coatings on some of the prototype
VersaBraille displays, after TS was trying to stop the ion migration
problem by coating the reeds. As it turned out, most of the coatings
made the problem of silver ion migration "snail trails" worse, as the
coatings had pin holes that concentrated the electric fields as if
they were pin points. Also, when insulating paints like polyurethane
were used, they thinned out at the sharp points of any rough metal
along the edges, even when the edges were polished smooth or even cut
back a bit from the edge of the piezo reeds.
Finally, I talked to a material scientist friend at Los Alamos
National Labs, and he recommended that we use parylene, because it
forms conformable coatings that tend to stay thick, as they coat over
sharp points. The parylene coating process was expensive, but it
solved the ion migration shortout problems enough that TS could get
the VersaBraille into successful manufacturing. Many of the more
modern braille displays use piezo reeds with nickle electrodes, since
nickle ions do not dissolve in water condensate and migrate as badly as
silver.
In the case of TS braille cells, they use bimorphs with two layers of
piezo, with a center metal strip. TS had to grind down through the
end of one of the piezo reeds in the bimorph, in order to access and
solder to that center vane or electrode. They also ground small
notches on the sides of the soldered end of the reeds, to lock them
in place in the reed holders.
Some of the early TS reeds were a quarter of an inch wide, so the pin
end of half of the reeds had to have the corner ground off, to allow
the pin of the lower bimorph to pass up past the upper notched
bimorph. This meant that one of the two dots in each row of a
braille cell had a little less piezo force driving it.
Other versions of braille displays were able to simplify and avoid
this "corner cutting" by using thinner bimorph reeds that could be
side-by-side for each row of braille dots. That also made it possible
to cut down on the height of the cells, since there were only3 or 4
steps or layers of reeds for the 6 or 8 dot cells.
Sorry, for rambling through a lot more background than you probably
ever wanted.
I hope this helps.
Cordially,
Noel
At 11:06 PM 9/20/2020, you wrote:
Content-Transfer-Encoding: 8bitlisters.
Hello Noel. I must attend to some of your emails off list, but a
question: I observed that the optacon benders had a small bit of their
coating removed from their free ends to which the tactile pins were
affixed. Was this just for gluing, or was it something else?
Thanks, and an interesting message you posted here.
Charles
On 2020-09-20 11:21 a.m., Noel Runyan wrote:
Tech alert! Apologies if the following may be too techy for most
forWannes,
A point of clarification. The monomorph reeds for the original
Optacon were not already available off the shelf for phonograph
cartridges in the early 1970s. Clevite made the reeds custom for
Telesensory Systems, because they had to be long enough to have a
resonant peak at 250 hertz, to match the 250 hertz peak response of
the particular tactile sensors of the human finger tip.
The typical off-the-shelf ceramic phonograph cartridges of the early
1970's were using monomorph piezo reeds, but they were much shorter
than the 1.5 inch Optacon reeds.
In contrast to the Optacon's monomorph reeds, the piezo reeds
Telesensory Systems used in their braille displays are called
bimorphs, because they use two layers of piezo material. The reeds
used for braille displays have to be wider, more powerful, and are
not driven at resonance by an alternating signal.
Another significant difference between the Optacon reeds and braille
display reeds is that Optacon reeds had silver metal coatings, unlike
the braille cell reeds that use nickle metal coatings. The nickle
metal plating (sometimes with Parylene Conformal overcoating) was
required to solve the problems we had with silver ion
migration. Silver ion migration was not a problem for the Optacon
reeds because they were being driven with an alternating voltage,
rather than with DC voltages, as is the case for braille reeds.
I have something like a thousand of the original Optacon reeds, still
in their original shipping containers, if you need several hundred
for a prototype system.
If you are interested, feel free to contact me off list.
Cordially,
Noel
-
Noel H. Runyan
Phone: 1-408-866-7564
Email: Noel@xxxxxxxxxxxxxxxxxxxxxxx
-
At 12:33 PM 9/20/2020, you wrote:
Hi Charles,
When you say the vibrotactile display being "prototypable" easier and
devices,as off thefar less cost, can you elaborate?
As I understand it, in the 1970's the piezo reeds were available
shelf parts for record cartridges.
Nowadays the smallest piezo reeds available are those for braille
problemat 2mm wide.
The piezo reeds for the optacon are only 1mm wide. This creates a
dollarsfor workholding the reeds when they are being machined.
The few manufacturers that I contacted quoted me several thousand
dmarc-noreply@xxxxxxxxxxxxx>for 500 piezo reeds.
Kind regards,
Wannes Sels
On Sun, Sep 20, 2020 at 7:59 PM CHARLES POND <
andwrote:
Aside from being computer compatible, and with room for development,
morea few other lesser details like a slightly bigger display and many
technologytactile-actuators than the 144 pins of the R1C/D, and a smaller
footprint, the only real big advantages of the pre-pprototype
farhere is that one can build the vibrotactile displays easily and for
message to:a message to:less cost. Even so, a thousand mamoolian is beyond many blind people
because they do not have a whole lot of readily disposable income.
P.S. In the interest of full disclosure I acknowledge that I am not
photon-dependent.
Charles
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