1. Field of the Invention
The present invention relates to mosaic ink recorders operated by piezoelectric drive elements, and in particular to a screen for such a recorder which renders the recorder substantially less sensitive to disturbances which would otherwise result in ink flow in the channels at undesired times.
2. Description of the Prior Art
A mosaic ink recorder having a recording head containing a number of ink channels which communicate an ink reservoir with a nozzle plate provided with a like number of outlet nozzles in registry with the ink channels, and having a piezoelectric drive element associated with each channel which is actuated to discharge ink from the respective channel is known from U.S. Pat. No. 4,158,847. The piezoelectric drive elements are tubular transducers which surround a portion of the ink channels. The ink channels are connected to an ink reservoir via a distributor and by selected operation of the piezoelectric elements a surge wave is produced in respective ink channels so that a droplet of ink is ejected from the respective outlet opening. During a suction phase of operation, ink is absorbed from the ink reservoir and at the same time a negative ink meniscus is produced at the outlet opening of the channel. Air is sucked in through the outlet opening as a result of the capillary action of the extremely small outlet opening. This blocking effect is desireable in that the ink which is trapped thereby in the ink channel blocks further flow of ink from the channel until the piezoelectric element is again actuated.
This blocking effect may be impaired, however, if the ink recorder is exposed to heavy vibration or other types of mechanical disturbances. Under these circumstances, air may be sucked in via the outlet opening and will considerably impair the printing process and may even render the process impossible.
Such an undesired effect may occur in ink recorders operating in accordance with the so-called under pressure process, either during a rest state or during pauses in the printing process. In such situations, that is, when ink is not being ejected through the nozzles, the ink remaining in the respective channels forms a negative meniscus in each of the outlet openings of the nozzle plate, and in the event of additional unchecked motion of the recording head this meniscus may extend inwards into the channel to such an extent that the blocking action of the outlet opening is overcome and unwanted ink flow occurs.