This invention generally relates to non-impact printing and, in particular, to high speed printing using a plurality of electrically controlled liquid ink jets.
In an ink jet printer, the print head structure may be a multiple nozzle type, with the nozzles aligned in a vertical line and supported on a print head carriage which is caused to be moved or driven in a horizontal direction for printing in a line manner. The ink droplet drive elements or transducers may be positioned in a circular configuration with ink passageways leading to the nozzles. Alternatively, the printer head structure may include a plurality of equally spaced horizontally aligned single nozzle print heads which are caused to be moved back and forth horizontally to print successive lines of dots making up the lines of characters. In this latter arrangement, the drive elements or transducers are individually supported along a line of printing.
There are a number of ways to generate an ink droplet. This invention is concerned with piezoelectric transducers as the drive elements. Heretofore, most such devices have been manufactured as single jets and then assembled into arrays. The single jets are operated to eject droplets on demand in contrast to creating droplets from a continuous jet where the piezoelectric device simply is used as a modulating drive means. Such continuous ink jet systems require special apparatus for deflecting the droplets and collecting the ink that is not destined for the printing medium. This invention is not concerned with continous ink jet systems.
The resolution of the printing system is generally measured in "dots per inch". In ink jet systems, a high resolution requires close spacing of the jets. Manufacturing single jet devices assembled into arrays is costly, particularly for heads containing a large number of jets. While print heads comprising arrays of single jets have been manufactured using standard piezoelectric crystals, they suffer from several disadvantages. Specifically, since piezoelectric crystals are brittle and must themselves be grown from crystals, they require careful handling in production. More importantly, these characteristics limit the minimum thickness and maximum size of the crystals. Another major factor in using piezoelectric crystals is that their dielectric breakdown limits the voltage that can safely be applied. As a result of these physical properties, the number of jets that can be assembled or placed in a given area is limited. Present constructions would require the stacking of several head assemblies.
Examples of prior ink jet print heads using piezoelectric crystals or like transducers are shown in U.S. Pat. Nos. 4,415,909 to Italiano et al, dated Nov. 15, 1983; 4,418,354 to Perduijn, dated Nov. 29, 1983 and 4,418,356 to Reece, dated Nov. 29, 1983.
Another form of ink printing device using a piezoelectric drive element is shown in U.S. Pat. No. 4,379,246 to Guntersdorfer, dated Apr. 5, 1983, wherein a piezoelectric drive element surrounds an ink channel of a writing jet in a mosaic printing device. The drive element is a winding formed by plies of thin synthetic foil having piezoelectric properties. In this apparatus, the foil is cut into individual pieces. U.S. Pat. No. 4,282,532 to Markham, dated Aug. 4, 1981, shows an ink jet apparatus using a thin film piezoelectric exciter for drop generation. However, the piezoelectric film is used in a continuous jet apparatus for modulation purposes.
It would be quite advantageous if multiple individual jets could be built on a common substrate with very close spacing, to yield a high dot per inch resolution capability not heretofore available. This invention is directed to satisfying this and other needs and solving problems with prior ink jet printing heads or the like.