This invention relates generally to the field of digitally controlled printing devices, and in particular to continuous ink jet printheads which integrate multiple nozzles on a single substrate and in which print nonprint operation is effected by controlled deflection of the ink as it leaves the printhead nozzle.
Many different types of digitally controlled printing systems have been invented, and many types are currently in production. These printing systems use a variety of actuation mechanisms, a variety of marking materials, and a variety of recording media. Examples of digital printing systems in current use include: laser electrophotographic printers; LED electrophotographic printers; dot matrix impact printers; thermal paper printers; film recorders; thermal wax printers; dye diffusion thermal transfer printers; and ink jet printers. However, at present, such electronic printing systems have not significantly replaced mechanical printing presses, even though this conventional method requires very expensive setup and is seldom commercially viable unless a few thousand copies of a particular page are to be printed. Thus, there is a need for improved digitally controlled printing systems, for example, being able to produce high quality color images at a high-speed and low cost, using standard paper.
Inkjet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing. Ink jet printing mechanisms can be categorized as either continuous ink jet or drop on demand ink jet. Continuous ink jet printing dates back to at least 1929. See U.S. Pat. No. 1,941,001 to Hansell.
U.S. Pat. No. 3,373,437, which issued to Sweet et al. in 1967, discloses an array of continuous ink jet nozzles wherein ink drops to be printed are selectively charged and deflected towards the recording medium. This technique is known as binary deflection continuous ink jet, and is used by several manufacturers, including Elmjet and Scitex.
U.S. Pat. No. 3,416,153, which issued to Hertz et al. in 1966, discloses a method of achieving variable optical density of printed spots in continuous ink jet printing using the electrostatic dispersion of a charged drop stream to modulate the number of droplets which pass through a small aperture. This technique is used in ink jet printers manufactured by Iris.
U.S. Pat. No. 3,878,519, which issued to Eaton in 1974, discloses a method and apparatus for synchronizing droplet formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates.
U.S. Pat. No. 4,346,387, which issued to Hertz in 1982 discloses a method and apparatus for controlling the electric charge on droplets formed by the breaking up of a pressurized liquid stream at a drop formation point located within the electric field having an electric potential gradient. Drop formation is effected at a point in the field corresponding to the desired predetermined charge to be placed on the droplets at the point of their formation. In addition to charging rings, deflection plates are used to deflect the drops.
Conventional continuous ink jet utilizes electrostatic charging rings that are placed close to the point where the drops are formed in a stream. In this manner individual drops may be charged. The charged drops may be deflected downstream by the presence of deflector plates that have a large potential difference between them. A gutter (sometimes referred to as a xe2x80x9ccatcherxe2x80x9d) may be used to intercept the charged drops, while the uncharged drops are free to strike the recording medium. In the current invention, the electrostatic tunnels and charging plates are unnecessary.
It is an object of the present invention to provide a high-speed continuous ink jet apparatus and method whereby drop formation and deflection may occur at high repetition.
It is another object of the present invention to provide a method of producing continuous the jet printing apparatus utilizing the advantages of selecting processing technology offering low cost, high volume methods of manufacture.
It is yet another object of the present invention to provide an apparatus and method for continuous ink jet printing that does not require electrostatic charging tunnels or deflection plates.
In accordance with an aspect of the invention, apparatus is provided for controlling ink in a continuous ink jet printer in which a continuous stream of ink is emitted from a nozzle wherein the apparatus comprises a reservoir of pressurized ink, an ink staging chamber having a nozzle bore to establish a continuous flow of ink in a stream, ink delivery means intermediate said reservoir and said staging chamber for communicating ink between said reservoir and said staging chamber, said channel means comprising a primary ink delivery channel and an adjacent secondary ink delivery channel; and a thermally actuated valve positioned, when closed, to block ink flow through said secondary channel and, when opened, to permit ink flow through said secondary channel, whereby opening and closing of said valve results in deflection of said ink stream between a print direction and a non-print direction.
In accordance with another aspect of the invention, there is provided a method of fabricating a continuous inkjet printhead having a series of inkjet devices each of which includes primary and secondary ink delivery channels, an ink staging chamber having a chamber wall with a nozzle bore aligned with said primary ink delivery channel and a thermally actuated valve positioned over said secondary delivery channel to control, by opening and closing of said valve, deflection of an ink stream emitted from said nozzle bore between print and non-print directions. The fabrication method comprises providing a silicon substrate having a front side and a back side; forming a series of first and second adjacent wells in the substrate corresponding to said primary and secondary ink delivery channels; and depositing a patterned thermally actuated valve device over each of said second wells. The method also includes depositing and patterning sacrificial material over said wells to form a volume corresponding to said ink staging chamber; depositing a chamber wall material over said sacrificial material to define an ink staging chamber wall; etching a nozzle bore in the chamber wall aligned with said first well; and removing said sacrificial material through said nozzle bore thereby forming said ink staging chamber with said valve device released within the chamber. The method further includes etching a channel through the back side of said substrate to said wells to form said primary and secondary ink delivery channels to said ink staging chamber.
These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.