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(11) | EP 0 273 664 A3 |
(12) | EUROPEAN PATENT APPLICATION |
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(54) | Droplet ejectors |
(57) Provision is made for varying the size of the pixels or spots printed by an acoustic
printer of the type in which one or more droplet ejectors (12) are driven by rf voltage
pulses to produce focused acoustic beams (22) for ejecting droplets (25) of ink on
demand from a free surface (24) of an ink supply (23). It has been found that the
size of the individual droplets (25) of ink that are ejected from the free surface
(24) of the ink can be varied by modulating the frequency, duration or amplitude of
the pulses applied to such a droplet ejector (12). Furthermore, it also has been found
that the trajectory along which the ink droplets (25) are propelled from the free
surface (24) of the ink supply to a nearby record medium (11) is sufficiently well
defined and repeatable that multiple droplets (25) can be deposited on the record
medium (11) in rapid sequence, one on top of the other, before the ink has time to
dry, to print variable diameter pixels or spots. The control techniques discribed
in this application may be employed for variable resolution printing and for imparting
a controlled pseudo-gray scale shading to the printed image. Each of the pixels of
the printed image may be composed of a single cell for one spot per pixel printing
or may be subdivided into a plurality of cells for multiple spot per pixel printing.
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