Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-10-15
2004-08-31
Vo, Anh T. N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06783213
ABSTRACT:
COPYRIGHT NOTICE
®2002 PicoJet, Inc. A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 37 CFR §1.71(d).
TECHNICAL FIELD
The present invention provides a piezoelectric ceramic ink jet print head made by an ultrasonic bonding process. Specifically, the invention provides several improved features of ink jet print heads, including a more cost-effective bonding process using an ultrasonic bonding technique, an improved piezoelectric ceramic crystal pattern, and improved print head-piezoelectric electrical contacts. Further, the present invention provides an ultrasonic bonding process joining metallic objects with ultrasonic energy.
BACKGROUND OF THE INVENTION
Joining metal plates had generally been done through welding or soldering processes. However, such processes alter the surface character of the object or provide for excess bonding material that can leak out and affect the formed object. Therefore, there is a need in the art to provide for a better process for joining metal, particularly metal plates in a high precision manner without leaking bonding material or altering surface characteristics. There is also a need in the art to improve such bonding processes, particularly in the assembly of ink jet printing heads. The following invention was made to address these needs.
Ink-jet printing is a non-impact dot matrix printing technology in which droplets of ink are jetted from a small aperture directly to a specified position on a media to create an image. The mechanism by which a liquid stream breaks up into droplets led to the introduction of the Mingograph, one of the first commercial ink-jet chart recorders for analog voltage signals. In the early 1960′s, Sweet of Stanford demonstrated that by applying a pressure wave to an orifice, the ink stream could be broken into droplets of uniform size and spacing. When the drop break-off mechanism was controlled, an electric charge could be impressed on the drops selectively and reliably as they formed out of the continuous ink-stream. The charged drops, when passing through an electric field, were deflected into a gutter for recirculation, and those uncharged drops could fly directly onto the media to form an image. This process became known as a continuous ink-jet. By the 1970′s, the IBM 4640 ink-jet printer was introduced as a word-processing printer.
Ink-jet systems, and in particular drop-on-demand ink-jet systems, are well known in the art. The principle behind an impulse ink-jet is the displacement of ink in an ink chamber and subsequent emission of ink droplets from the ink chamber through a nozzle. A driver mechanism is used to displace the ink in the ink chamber. The driver mechanism typically consists of an actuator, often referred to as a transducer, such as a piezoelectric material bonded to a thin diaphragm. When a voltage is applied to the actuator, it attempts to change its planar dimensions, but, because it is securely and rigidly attached to the diaphragm, bending occurs. This bending displaces ink in the ink chamber, causing the flow of ink both through an inlet from the ink supply to the ink chamber and through an outlet and passageway to a nozzle. In general, it is desirable to employ a geometry that permits multiple nozzles to be positioned in a densely packed array. However, the arrangement of ink chambers and coupling of ink chambers to associated nozzles is not a straightforward task, especially when compact ink-jet array print heads are sought. The relatively large size of the actuator required to effectively expel ink drops is a major problem limiting the packing density of ink-jet array print heads.
Other apparatus and methods for increasing the packing density of ink-jet arrays employ electrostrictive materials as actuators. In particular, U.S. Pat. No. 5,087,930 describes a compact ink-jet print head having an array of closely spaced nozzles that are supplied from densely packed ink pressure chambers by way of offset channels. The ink supply inlets leading to the pressure chambers and the offset channels are designed to provide uniform operating characteristics to the ink-jet nozzles of the array. To enhance the packing density of the pressure chambers, the ink supply channels leading to the pressure chambers and offset channels are positioned in planes between the pressure chambers and nozzles. The ink-jet print head is assembled from plural plates with features in all except a nozzle-defining plate being formed by photo-patterning and etching processes without requiring machining or other metal working.
The pressure chambers are driven by ink-jet actuators employing a piezoelectric ceramic, such as lead zirconate titanate (“PZT”). A predetermined amount of mechanical displacement is required from the PZT actuator to displace ink from the pressure chamber and out the nozzles. The displacement is a function of several factors, including: PZT actuator size, shape, and mechanical activity level; diaphragm size, material, and thickness; and the boundary conditions of the bond between the actuator and the diaphragm.
PZT is permanently polarized to enable mechanical activity, which is dependent upon the level of polarization as well as other material properties. To polarize PZT, an electric field is applied such that domains in the PZT are oriented to align with the electric field. The amount of polarization as a function of electric field strength is nonlinear and has a saturation level. When the polarizing electric field is removed, the PZT domains remain aligned resulting in a net polarization referred to as a remnant polarization. Alignment of the PZT domains causes a dimensional change in the material. Subsequent applications of an electric field causes a dimensional change that is linear with respect to applied electric field strength.
Unfortunately, PZT has a number of properties that can reduce its mechanical activity over time. For instance, applying an electric field in a direction opposite to the initial remnant polarization can cause a reduction in the amount of polarization. Likewise, cyclic variations of an applied electric field in the direction opposing the polarization can cumulatively and continuously degrade the polarization.
PZT has a property referred to as the Curie point, a temperature at which the remnant polarization in the material becomes zero. Because PZT material is not entirely uniform, there is a range of temperatures over which some but not all of the polarization is lost. The polarization loss is not instantaneous, thereby defining a time-temperature level that should not be exceeded.
PZT actuators have various shapes, including disks and rectangular blocks. Polarization ensures that the PZT materials are anisotropic such that several “d” coefficients may be defined for each shape, in which each “d” coefficient relates a particular dimensional change to a particular direction of the polarization and applied field. For a typical disk-shaped actuator, a commonly employed “d” coefficient is the “d.sub.-” coefficient, which is a measure of the strain perpendicular to the direction of polarization when the electric field is applied in the direction of polarization. The strain is evident as a radial contraction in the actuator because d.sub.31 is negative. A high d.sub.31 value is indicative of high mechanical activity and is desirable for making efficient ink-jet arrays having a high packing density. Stability of the d.sub.31 value is necessary to maintain constant ink-jet performance over an extended time period.
Maintaining PZT actuator polarization during print head manufacturing is difficult for the following reasons. If a disk is bonded to a diaphragm before the disk is polarized, a significant permanent strain is introduced when the disk is polarized.
Le Hoi P.
Le Hue P.
Le Thanh P.
Tran Linh B.
PicoJet, Inc.
Stoel Rives LLP
Vo Anh T. N.
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