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 the breakup of a liquid ink stream into droplets is caused by a periodic disturbance of the liquid ink stream.
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.
Ink jet 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 tunnels, deflection plates are used to actually deflect drops.
Conventional continuous ink jet utilizes electrostatic charging tunnels 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. If there is no electric field present or if the drop break off point is sufficiently far from the electric field (even if a portion of the stream before drop break off is in the presence of an electric field), then charging will not occur. In the current invention, the electrostatic charging tunnels are unnecessary. Instead, the drop or drops that are desired to reach the recording medium may be selected by applying a relatively low energy pulse to the heater while a DC field may be placed on the deflection electrode that is located near the drop streams. This offers the advantage of low power consumption as well as the simplification and cost reduction of a DC field as opposed to a switchable field required in the prior art.
It is an object of the present invention to provide a high speed apparatus and method of page width printing utilizing a continuous ink jet method whereby drop formation and deflection may occur at high repetition.
It is another object of the present invention to provide an apparatus and method of continuous ink jet printing with drop deflection means which can be integrated with the printhead utilizing the advantages of silicon 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.
It is still another object of the present invention to obtain selection of drops for recording through the application of a relatively low energy pulse to the heater(s) resulting in low power consumption while utilizing a DC field for deflection.
According to one feature of the present invention, apparatus is provided for controlling ink in a continuous ink jet printer. An ink stream generator establishes a continuous flow of ink from a nozzle in a stream. A droplet generator causes the stream to break up into a plurality of droplets with an adjustable drop break off position having at least (1) a first drop break off position spaced from the nozzle and (2) a second drop break off position spaced from the first drop break off position. A stream deflector adjacent to the stream between the first drop break off position and the second drop break off position controls the direction of the stream between a print direction and a non-print direction.
According to another feature of the present invention, a process is provided for controlling ink in a continuous ink jet printer in which a continuous stream of ink is emitted from a nozzle. A continuous flow of ink in a stream is established, in which the stream breaks up into a plurality of droplets with at least (1) a first drop break off position spaced from the nozzle and (2) a second drop break off position spaced from the first drop break off position. The ink stream is deflected between the first drop break off position and the second drop break off position to thereby control the direction of the stream between a print direction and a non-print direction.
According to a preferred embodiment of the present invention, the droplet generator is a heater. The ink stream generator includes an ink delivery channel; a source of ink communicating with the ink delivery channel, wherein the ink is pressurized above atmospheric pressure; and a nozzle bore which opens into the ink delivery channel. An ink gutter is provided in the path of ink droplets traveling in only one of the print and non-print directions.
According to another feature of the preferred embodiment of the present invention, a deflection apparatus is associated with the ink delivery channel to deflect the ink stream. The stream deflector includes at least one deflection electrode; and a deflection circuit is adapted to apply a constant DC voltage to the deflection electrode to deflect droplets from one of the print and non-print directions to the other of the print and non-print directions.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiments presented below.