Digital BW, The Print

----- Original Message -----
From: "Martin Sluka" <martinsluka@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Monday, March 03, 2003 9:49 AM
Subject: Re: [Digital BW] Canon i9100


> At 09:07 +0100 3.3.2003, Ernst Dinkla wrote:
> *******************************************
>
> >
> >And Canon hasn't variable droplet sizes yet ?  Seems unlikely.
> >
>
> It is quite easy imagine how to produce two size of drop
mechanically
> - add two different electric potentials on the same
piezocrystal and
> you receive for example - 4 and 9 pl. Add more different drops
and
> you receive three possible sizes of drop in one step: 4, 9 and
22
> (9+9+4) pl. And 13 (4+9), 26 (4+9+4+9), 36 (4+9+4+9+4+9) pl for
360
> dpi.
>
> But how to make the same with thermal head? With two different
> thermal elements for one nozzle? Is it mechanically possible?
>
> Anytime you are limited with cooling of print head. So you may
not
> increase the frequency of firing of drops ad lib.  (IRIS has
solved
> it very effectively - there is a continual production of drops
which
> cool the head - with only ONE nozzle per color.)
>
> Very high number of nozzles has one positive effect though - it
> covers the irregularities of firing of drops better. Drops
fired by
> piezo are about 100 times faster and the precision is much
higher,
> but one may see any irregularity.

HP was one of the first to introduce variable droplets in desktop
inkjet printing. Voltage changes combined with a slightly faster
pulse will work as well I guess to get more ink pumped out.
Higher frequency pulses after another that will produce small
droplets that cling to one another to form one big droplet before
the ink hits the paper works as well. In the print there is no
distinction between a dot that is build by one larger varible
droplet created in the head, by a larger droplet that is created
in mid air or by a lot of smal droplets that hit the paper at the
same time at the same spot.

http://h20015.www2.hp.com/en/document.jhtml?lc=en&docName=bpu0218
2

Encads had pigment ink (GO) before the Rolands and the Epson
7500/9500 got pigment ink so there's no rule that thermoheads
can't print pigment ink. AFAIK the HP desktop printers had a
black ink a long time ago that didn't fade. Most likely that was
a pigment ink as well. All the modern wide format thermohead
inkjet printers can use pigment inks.

The Iris uses a piezo system where ink is squirted continuously
and the droplets that shouldn't hit the paper are deflected to a
waste bottle. Easy on ink cost calculation but it is expensive on
ink costs ;-) That was what most inkjet systems used in the
beginning, address label printing in postal offices etc. Later on
the "drop on demand" system was developed, harder to get the same
high frequency in interrupted ink streams as the Iris has in a
continuous stream. Epson managed to get frequency and added
droplet variation as well.

Piezoheads have some specs that will be difficult to achieve in
thermoheads. True solvent inks are not a nice match with heads
that work at high temperatures. The pumping capacity of
piezoheads is better suited for 'thicker" inks like textile
sublimation inks, UV curable and possibly the high load pigment
inks (Ultrachrome). Thermoheads are probably easier to
manufacture and it could be that for a given head surface more
nozzles can be applied. Spreading of nozzles over a larger area
can solve overheating problems and increase speed or resolution.

The death of thermoheads has been predicted a long time ago
..........I'm guilty too.

Ernst